Heparin-induced Thrombocytopenia Testing Research Articles

Evaluating Diagnostic Algorithms for Heparin-Induced Thrombocytopenia using Two Combined Automated Rapid Immunoassays.

Heparin-induced thrombocytopenia (HIT) is an autoimmune disorder caused by antibodies against platelet factor 4 (PF4) and heparin complexes. Rapid immunoassays (IAs) for detection of these antibodies mark a milestone in HIT diagnosis, despite a higher false-positive rate compared with functional platelet-activation assays. However, combining different rapid IAs may help to improve their diagnostic specificity. Here, we compared the individual performance of the latex immunoturbidimetric assay (LIA; HemosIL HIT-Ab [PF4-H]; sensitivity 91.7%, specificity 68.4%) and chemiluminescence immunoassay (CLIA; HemosIL AcuStarHIT-Ab [PF4-H]; sensitivity 92.4%, specificity 85.8%) with their combined performance using two unique diagnostic algorithms in a single prospective cohort of suspected HIT patients. Using the simultaneous algorithm adapted from Warkentin et al, the combined LIA-CLIA had a sensitivity of 99.0% and specificity of 64.3%. The sequential algorithm adapted from Rittener-Ruff et al was applied in two theoretical scenarios to reflect real-world circumstances in diagnostic laboratories where access to clinical information is limited: (1) assuming all patients had an intermediate 4Ts score and (2) assuming all patients had a high 4Ts score. This algorithm correctly predicted HIT in 94.5% (high 4Ts) and 96.0% (intermediate 4Ts) and excluded HIT in 82.6% (high 4Ts) and 80.1% (intermediate 4Ts) of patients in either scenario, respectively. Although both combined algorithms improved diagnostic performance of individual IAs, the simultaneous algorithm showed fewer false predictions (7.9%) than the sequential algorithm (intermediate 4Ts: 37.6% and high 4Ts: 41.5%) and proved more practical as it does not rely on physician evaluations. Our findings highlight the importance of accounting for clinician and interlaboratory variability when evaluating diagnostic tests for HIT.

When HIT Testing Hurts- the Financial and Clinical Repercussions of Heparin Induced Thrombocytopenia Testing: A Single Center Analysis

Introduction: Thrombocytopenia is a common inpatient hematologic concern. Most often, thrombocytopenia is a multifactorial phenomenon, without one clear cause. Heparin Induced Thrombocytopenia (HIT) is a rare but serious hematologic consequence of exposure to heparin. In many hospitalized patients, heparin is routinely used as venous thromboembolism (VTE) prophylaxis or for therapeutic anticoagulation. The incidence of HIT is approximately 0.5-1.0% in patients exposed to unfractionated heparin (UFH). Though rare, there seems to be over-testing of HIT antibody in the inpatient setting. As such, there is potential for high cost with low yield and false positives that alter patient management, resulting in prolonged hospital stays and further complications in patient care. Methods: This was a retrospective, observational study reviewing the indications, results, and patient characteristics of cases in which HIT testing was ordered. Indications for testing and influence of results on management were determined based on clinical documentation. The tests of interest included HIT antibody testing and Seratonin Release Assay (SRA). We analyzed how many times a HIT antibody was positive with a negative result in the SRA. We also determined whether there was an increased length of stay in patients who had HIT testing ordered. The study population included patients who were admitted to University of Florida Shands Medical Center, an academic institution in Jacksonville, FL in 2022. All patients were >18 years of age. Results: 190 patients were identified, for whom 190 HIT antibody tests were ordered and 75 SRAs. All patients who had a SRA performed had exposure to low dose heparin or therapeutic high dose heparin. Out of 190 patients, HIT testing was positive in 30 patients (15.8%). SRA testing was performed on 75 patients despite only 30 positive HIT tests. The true positives were 10 patients who had positive SRA confirmatory testing out of 190 patients with suspected HIT. Based on the results of confirmatory testing, the false positive fraction of HIT testing was 66%. When analyzing the 190 patients who underwent HIT testing, the average length of stay was 14 days. On average, a hospital stay in the US is 5.5 days and evaluation of HIT results in 8.5 additional days of hospital admission at our institution. The prolonged length of stay for HIT testing is likely impacted by awaiting SRA results along with other factors. Conclusion: This analysis examines the relative over-testing for HIT at a single institution. Compared with the known incidence of positive HIT tests, there is a significant number of positive HIT antibody tests at our hospital. The data further reveals a high probability of a false positive HIT antibody test results in the hospitalized patient, possibly due to immune reactivity. Of 190 patients suspected with HIT, only 10 patients had a positive confirmatory SRA, indicating that only 5% of suspected patients truly had HIT. This demonstrates that 95% of the time HIT assays ordered did not provide clinically useful information. From the time work up was initiated to the time of discharge, the average stay length was 14 days in a patient suspected with HIT. Cost burden of HIT testing was evaluated. Each HIT panel is $153.83 and each confirmatory SRA test is approximately $250, at a commercial laboratory. Taken together, the total average cost per patient with suspected HIT is $413.83 in diagnostic testing. Prolonged hospital stay contributes to approximately $25,000 increase in hospital stay per patient being evaluated for HIT. This does not include the cost of further work up or interventions. Changing to an alternate anticoagulant such as Argatroban increased costs by nearly $1,500 per case and this number increased further when adding the daily coagulation panel required while on this drug. In other studies, this cost has been estimated to add $90,000 to the hospital stay. Prolonged hospital stays are also associated with unintended incidents such as GI bleeding leading to blood transfusions, invasive testing (such as endoscopy/colonoscopy) and increased morbidity to the patient. We will use this information to implement a tool in our Electronic Medical Record (EMR) that will require answering the 4T score in order to establish high pre-test probability, prior to ordering HIT antibody testing at the University of Florida in Jacksonville.

Comparison of Interobserver Agreement between the 4T and the HIT Expert Probability (HEP) Scores: We Agreed Not to Agree

Background: Diagnosis of heparin induced thrombocytopenia (HIT) is challenging. The 4T score is the principal scoring system for HIT. The HIT Expert Probability (HEP) score, based on expert opinion, was proposed in 2010. Both scores have a very high sensitivity, being capable of ruling out HIT in low-risk individuals. However inter-observer agreement (IOA) of HEP score in comparison to the 4T score remains uncertain. Aim: This study aimed to compare IOA between the 4T and the HEP score among hospitalized patients. Specific objectives: Comparison of IOA between the 4T and the HEP score in the 1-whole cohort 2-non-ICU 3- ICU Identify which item of the score have the lowest IOA (magnitude of thrombocytopenia, timing of thrombocytopenia, existence of other causes of thrombocytopenia, presence of thrombosis) Methods: Patients: This is a retrospective study at a single tertiary hospital. All inpatients 16 years or older who have been tested for HIT between June 2019 to end of June 2021 were included. Patients were excluded if the reason for sending HIT was a repeat test. Data were collected retrospectively by manual chart review. Assessment of HEP score and 4Ts score: Two hematologists rated the HEP score and 4Ts score independently for every patient. The score's calculation was blinded between observers and, they were blinded to the HIT Eliza result. Low 4Ts score is defined as score less than 4 and for HEP score if less than 3. HIT test was done using Stago Asserachrom HPIA-IgGAM ELISA with level of < 0.4 considered negative. Statistical analysis: Continuous variables are reported as mean ± standard deviation (SD) or median (interquartile range; IQR), as appropriate. Categorical variables are reported as frequency and percentage. The Kappa coefficient (к) with 95 % confidence interval (CI) was used to assess the IOA of 4T score and HEP score, it was calculated for the individual risk categories - low vs high score in: 1-the whole patients 2-ICU 3- non-ICU We also calculated the IOA for each item of the score, magnitude of thrombocytopenia, timing of thrombocytopenia, existence of other causes of thrombocytopenia, presence of thrombosis (as total score). A P-value less than 0.05 was considered significant. Statistical analyses were performed using SAS version 9.4 (SAS institute, CARY, NC, USA). The study was approved by the local ethical board. Informed consent was waived. Results: After exclusion of the repeat test (13), 302 patients were included in this study. Median age 66 years old. Most common reason for request was thrombocytopenia 288 (95%). HIT ELISA ≥ 0.4 in 34 (11%). Inter-observer agreement: All patients: We found similar IOA between the 4T score and the HEP score к (95 % CI) of 4T score was .14(-0.13-0.41, P < 0.01), compared 0.17(-0.16-0.5, P < 0.01) in the HEP score. Non-ICU patients: The IOA was similar between the 4T score and the HEP score, к of 4T score was 0.24(0.11-0.38, P < 0.01) compared 0.17(0.03-0.31 P < 0.01) in the HEP score. ICU patients: The IOA of 4Tscore was lower than HEP score к of 4T score was -020(-0.20.16, P = 0.83) compared 0.16(-0.037-0.37, P = 0.86) in the HEP score. Among the four individual items of 4T score, “existence of other causes of thrombocytopenia” achieved the lowest к with 0.03 and 0.1 in 4Tscore and HEP score respectively. Conclusion: In this retrospective study, we found a lower interobserver agreement of the 4T score compared to the HEP score in ICU patients. The poor IOA of the 4T score in ICU patients is attributed to worse agreement in (existence of other causes of thrombocytopenia item). Ascertaining the cause of thrombocytopenia in ICU patients is challenging and the 4T score seems to depend on physician gestalt rather than objective points. Our data suggests that the HEP score is the preferred score in in patients with critical illness.

3Ts Score, an Attempt for Less Testing in Thrombocytopenia Patients with Suspected Heparin Induced Thrombocytopenia (HIT): Retrospective Analysis in a University Hospital Setting

Background: Heparin-induced thrombocytopenia (HIT) is a prothrombotic and potentially fatal adverse drug reaction mediated by platelet-activating antibodies against multimolecular complexes of platelet factor 4 (PF4) and heparin. The 4Ts is a pretest scoring system for HIT that was developed to improve and standardize clinical diagnosis. The strength of the 4Ts score lies in the negative predictive value of a low pretest probability score. Those with a 4T score ≥4 is considered to have moderate to high probability of HIT and should undergo confirmatory laboratory test. Delays in treatment are associated with risk of thrombosis. Immediate cessation of heparin and initiation of a non-heparin anticoagulant is therefore standard of care. Method: This is a single institutional retrospective study. We reviewed the charts of 219 patients with thrombocytopenia with suspected HIT to evaluate the appropriateness of ordering the HIT testing based on the pretest probability of the 4Ts scoring system. All patients had enzyme linked immunosorbent assay (ELISA) test for HIT antibodies (the screening test). We studied tests that were sent from 03\16\2021 through 07\03\2023. The serotonin release assay (SRA) which is the confirmatory test for HIT was only sent for patients who had a positive ELISA test. 4T scores were calculated retrospectively using chart's information available to clinicians at the time of the HIT tests were sent. Results: Out of the 219 patients, 80(36.5%), 120(54.7%) and 19(8.6%) patients had a low, intermediate and high pretest probability respectively. The HIT ELISA test was positive in 33 (15.7%) patients and 196 (84.9%) patients had negative results. HIT ELISA had 100% and 93.5% sensitivity and specificity respectively while the positive and negative predicative values were 60% and 100% respectively. A positive SRA test was reported in 23 patients (10.5% of the total study population). Seventy-nine patients (36% of our total sample) scored 4 points which represents intermediate pretest probability. Out of these 79 patients only 6 (11.3%) patients had a positive ELISA test, and 5 (6.3%) patients had a positive SRA test. Aiming to minimize the HIT over testing we examined the increase in the cutoff point of the intermediate pretest probability from 4 points to 5 points which resulted in significant increase in the sensitivity and positive predictive value of the intermediate pretest probability (75.4% and 21% versus 39% and 12.9% respectively). However, the sensitivity dropped from 90% to 65%. The 4th part of 4Ts score gives points based on the probability of HIT versus other pathology as a cause of the thrombocytopenia. Most of the patients with suspected HIT will score one point out of the 4th part of 4Ts score which makes this part of the score is less helpful in distinguishing between patients with suspected HIT and will result in higher overall pretest probability and more testing. We studied the 3Ts score (the 4Ts scoring system after elimination of the 4th part) effect on the intermediate pretest probability. The cutoff points for the 3Ts score are 1-3, 4-5 and 6 for low, intermediate and high pretest probability respectively. The 3Ts score model resulted in significant increase in the specificity and the positive predictive value (76% and 21.7% versus 39.2% and 12.9% respectively) however the sensitivity dropped from 90% to 65%. The average turnaround time for HIT ELISA test and the SRA test was 2.3 days and 4.4 days respectively. Fifteen patients (21% out the patient had low pretest probability on the 4Ts score), 41 patients (59% of the patient who had an intermediate pretest probability on the 4Ts score) and 13 patients (18.8% of the patients who had high pretest probability on the 4Ts score) started on non-heparinoid anticoagulation meanwhile awaiting on the HIT testing result. Conclusion: Over testing of HIT is common secondary to underuse of 4Ts scoring system. Multicomponent educational interventions to increase the awareness and utility of the 4Ts score in addition to implantation of clinical decision support based on HIT computerized score will help to reduce unnecessary diagnostic testing of HIT in patients with low pretest probability. Increasing the cutoff point of the intermediate pretest probability or applying the 3Ts score model resulted in significant increase in the specificity and the positive predictive value of the 4Ts scoring system on expense of the scoring system sensitivity.

The Impact of Laboratory Sample Request Evaluation and the Use of Probability Testing for HIT By Trained Physician on the Decrease of Unnecessary Tests and Increase the Likelihood of Positivity

Introduction: Heparin-induced thrombocytopenia (HIT) is an extremely serious and potentially fatal condition that can develop in patients taking heparin-based medications, such as unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH). The laboratory tests for diagnosis of HIT is expensive and time consuming. Clinical assessment (4Ts) followed by testing for Heparin/platelet factor 4 antibody in intermediate and high risk patients is the standard algorithm of pretest for (HIT) which can be later confirmed by serotonin releasing assay if available. Materials and methods: We conducted a retrospective analysis of laboratory practice of pretest evaluation of samples submitted for HIT testing in a cohort of patients treated in a tertiary hospital in Saudi Arabia who had a clinical suspicion of HIT. The 4 T score was a pretest requisite to proceed for electronic request for HIT. It had to be performed by the requesting physicians of different medical specialties. The request then been evaluated by hematopathologist before proceeding. The test will be cancelled if: the 4T score calculated by attending physician is < 4 or if platelet count is normal with no evidence of significant drop in the last 4 days from request or the test was performed at least 2 days before the new request. Additional exercise was performed by two physicians in training after train them to standardize the calculation of the 4T scores without re evaluation by the hematopatologist. The sample proceeded for testing if it met the testing criteria of 4T score > 3 and passed the evaluation by the hematopathologist. All tested sample were performed by immunoglobulin G (IgG) antibodies via an ELISA (Asserachrom HPIA-IgG, Stago Diagnostica STA®) and Optic density ( OD) and was evaluated and considered positive if OD >0.39 with sub classification to low positive 0.4-1, moderate 1-2 and strong if >2. Over a period of 2 years, we received 449 samples for patients who were admitted to our hospital, received prophylactic or therapeutic doses of LMWH or UFH, and underwent an HIT test due to clinical suspicion ( > 50% drop in platelet count from baseline, or ≥ 2 consecutive platelet counts < 150,000 per mm 3 and was defined as possible HIT). The 4 T score was calculated in the hospital system by attending physicians referred to as (system 4T score) and recalculated by trained two physicians and referred to (re calculated 4T score). Descriptive statistics, paired samples statistics, correlations, and analysis of variance (ANOVA) were performed. Results: The test was labeled by the laboratory physician ( hematopathologist ) as not indicated and test was not performed in 156 (35%) for various reasons including low 4 T score <3 in 90 (57%), Normal platelet count > 150 at time of test ( and wrong calculated 4T score) in 28 (18%), duplication of test order in 10 (6.4%%), There was clear other cause of thrombocytopenia in 15 (10%), Bad sample quality 5 (3.2%%) and 8 (5%) for other reasons. The samples for HIT test were for 231(51%) males and 220 (49%) females with mean age 56.3 (1-102) years. The mean platelet count at time of request was 82.9 (2-384) per mm 3. Out of the total cohort 422 (95.1%) patients had received UFH and only 22 (4.9%) received LMWH. There is only 69/449 (15.4%) agreement between the two calculations (system and re calculated score) . Out of the tested samples 293, total positive tests 19 (6.5%), were 11 (3.8%) had low positive for HIT test, moderate positive in 6 (2%) and only 2 strongly positive for HIT. The calculated (system 4T score) of < 4 were 142 (32%) samples while the (re calculated 4T score) were 136 (30%) of which 60 ( 38%) of the cancelled tests by hematopathologist, of which 68 (23%) of tested samples were negative and 7 (37%) of positive tests could have been missed based on this calculation. There were 12 out of 19 had moderate and high score by calculation and positive HIT while there were 17 out of 19 had moderate and high score by system calculation. Conclusion: We are reporting improved detection of HIT and confirmed the value of applying the 4 T score for HIT testing with added value of pre test screening to exclude low probability and cancel samples with no clear indication of HIT due to presence of other causes of thrombocytopenia.The retrospective re calculation even with more trained physicians did not add a value compared to pretest evaluation and screening by hematopathologist which had resulted in cancelation or more than third of the requested tests.

Implementation of 4T Score Documentation on PF4 Testing in Patients with Suspected Heparin-Induced Thrombocytopenia

Purpose: Heparin-induced thrombocytopenia (HIT) is a severe complication of heparin therapy. Diagnosis requires clinical evaluation and laboratory testing. The 4T score is a pretest clinical scoring tool used to determine the probability of HIT. A non-profit health system implemented mandatory documentation of 4T score calculation prior to ordering PF4 tests for suspected HIT patients. The purpose of this performance improvement project is to evaluate the implementation of 4T score documentation on PF4 testing and argatroban utilization. Methods: This was a retrospective, multi-site chart review of patients conducted to assess the impact of mandatory 4T score documentation prior to a PF4 order. The study included adult patients who were admitted to one of the practice sites between January 2020 and November 2022 with a suspicion of HIT and a PF4 order. The primary outcomes included the number of PF4 tests ordered and the percentage of positive PF4 results. Secondary outcomes included number of SRA orders and percentage of positive SRA results, turnaround time for SRA, and the utilization of argatroban. Data collection included baseline demographics, documentation of 4T score, PF4 results, SRA results, documentation of heparin allergy, initial anticoagulant prescribed, platelet trend, ordering provider, and duration of argatroban therapy in patients with a positive PF4 result. The analysis involved using χ2 test and Fisher's exact test for the primary outcomes. Results: Mandatory 4T score documentation significantly reduced PF4 orders by 68% over a two-year period (p<0.0001). It also improved the percentage of positive PF4 results from 12% to 24% (p=0.60) and positive SRA results from 19% to 44% (p=0.35). Notably, after documentation of the mandatory 4T score tool, only 21% of the patients had a PF4 order placed. A total of 42 patients with a positive PF4 test were included to assess argatroban utilization. The turnaround time for SRA in these patients was 3.6 days while duration of argatroban therapy was 6.8 days. Conclusion: Implementation of mandatory 4T score documentation significantly reduced PF4 orders and improved HIT diagnostic testing in a non-profit health system. Challenges remain with SRA turnaround time and corresponding duration of argatroban therapy. The results of this project have demonstrated that standardized documentation is essential for optimizing HIT diagnosis and management protocols. Future efforts will focus on optimizing confirmatory HIT testing and non-heparin anticoagulation therapy.

Improving Judicious Use of Heparin-Induced Thrombocytopenia Testing Through Electronic Health Record-Based Intervention.

Heparin-induced thrombocytopenia (HIT) is an immune-mediated drug reaction that can cause thromboembolism in the setting of thrombocytopenia. An enzyme-linked immunosorbent assay (ELISA)-based assay to screen for HIT antibodies (HAb) is available but has relatively low specificity and a correspondingly high false positive rate. The 4Ts score has been validated to determine the pretest probability of HIT. The authors hypothesized that an electronic health record (EHR)-based clinical decision support (CDS) tool incorporating the 4Ts score would reduce the volume of HAb orders. After implementing a CDS tool into the EHR, the researchers retrospectively evaluated the impact from November 2019 to October 2021, compared to a preintervention period (January to October 2019). The primary outcome was average tests per month. Secondary outcomes included rates of tests ordered per total inpatient encounters and proportion of HAb sent despite low 4Ts score in the postintervention study period. Of 1,833 HAb sent during the study period, 1,217 occurred in the postintervention period. In the postintervention period compared with the preintervention period, the average orders per month was 50.5 (standard deviation [SD] 9.7) vs. 61.6 (SD 7.2) (p = 0.003), and the order incidence rate was 8.0 per 1,000 patient encounters postintervention vs. 9.2 per 1,000 patient encounters preintervention (rate ratio [RR] 0.87, 95% confidence interval [CI] 0.79-0.96, p = 0.002). Postintervention, 252 (20.7%) had a 4Ts score calculated as low probability, 759 (62.4%) as intermediate probability, and 131 (10.8%) as high probability, and 75 had no associated 4Ts score. Implementation of a simple CDS tool reduced the rate of HAb orders, reducing unnecessary HAb testing.

Heparin-activated procoagulant platelet assay: a flow cytometry-based functional test for heparin-induced thrombocytopenia

BackgroundFunctional platelet activation assays are required for the diagnosis of heparin-induced thrombocytopenia (HIT). Due to their sophisticated methodology, they are only available in reference centers. ObjectivesTo evaluate the diagnostic accuracy of the flow cytometry-based heparin-activated procoagulant platelet (HAPP) assay in the laboratory diagnosis of HIT. MethodsProcoagulant platelets (PCP), defined by the expression of phosphatidylserine and CD62-P, were evaluated by flow cytometry in platelet-rich plasma from healthy donors after incubation with patient sera in the absence and presence of heparin. A sample was considered positive in HAPP assay, if the following 3 criteria were met: 1) the percentage of PCPs was ≥10.3% after incubation with 0.2 IU/mL heparin, 2) the fold increase in presence of 0.2 IU/mL heparin compared with buffer was ≥1.5, and 3) 100 IU/mL of heparin resulted in ≥50% inhibition of PCP. HAPP assay was validated in a prospective cohort (n = 202) of consecutive specimens submitted to our laboratory for serologic diagnosis of HIT. Heparin-induced platelet activation (HIPA) assay was used as the reference standard. ResultsHIT-positive sera induced PCPs in the presence of 0.2 IU/mL heparin, which was inhibited with 100 IU/mL of heparin. In the prospective validation cohort, there were 15 HIPA+ and 187 HIPA- sera. HAPP was positive in 20 samples in this cohort. Using optimized cut-offs, HAPP assay had a sensitivity of 93.3% and specificity of 96.8%. ConclusionHAPP assay is promising as a simple and reliable functional assay for HIT; however, further studies are needed to confirm our results in larger cohorts.

Next-generation diagnostic instruments in haematology.

Gallo et al. assessed the impact of implementing a clinical decision support tool in a multi-hospital setting. This is one of three important points to unlock the capabilities of the next-generation of diagnostic instruments: (a) integrating diagnostic information from various sources, (b) ensuring accurate development and validation in well-designed clinical studies and (c) seamlessly integrating them into clinical practice. Commentary on: Gallo et al. Clinical decision support to reduce unnecessary diagnostic testing for heparin-induced thrombocytopenia. Br J Haematol 2023;202:1011-1017.

A Modified 4Ts Score for Heparin-Induced Thrombocytopenia in the Mechanical Circulatory Support Population

To identify risk factors and develop a pretest scoring system to differentiate patients with heparin-induced thrombocytopenia (HIT) in the mechanical circulatory support (MCS) population. The authors present a modified "4TMCS" scoring system, which considers the "type of mechanical circulatory support" that may help identify patients at risk for developing postoperative HIT. A retrospective cohort study. Patients who underwent cardiac surgery were categorized into 3 groups: (1) normal platelet count, (2) thrombocytopenia with a negative HIT test, and (3) thrombocytopenia with a positive HIT test. A comparison of diagnostic accuracy between the 4Ts and 4TMCS probability scores was performed. At a single adult tertiary-care center. A total of 5,314 patients who underwent cardiac surgery between May 1, 2008 and December 31, 2016. None. In total, 125 out of 5,314 patients (2.4%) were diagnosed with HIT, of whom 75 out of 5,314 (1.4%) had clinical evidence of thrombosis. Overall, in-hospital mortality was 25.6%, 11.7%, and 1.5% in the HIT(+), HIT(-), and control groups, respectively (p < 0.001). Mechanical circulatory support was associated with a significantly increased risk for HIT, with an incidence of 5.9% in patients receiving MCS versus 1.9% in those without (p < 0.001). Area under the receiver operator curve (AUC) analysis demonstrated improved diagnostic accuracy of the 4TMCS score compared with the 4Ts (AUC=0.83 v 0.77, p < 0.044). The 4TMCS score had higher sensitivity than the 4Ts, using the guideline-recommended score cutoff of ≥4 (95.2% v 85.7%). Heparin-induced thrombocytopenia is associated with worse outcomes and increased morbidity and mortality in the MCS population. Awareness of patient risk factors and the application of a modified 4TMCS probability score may allow for more accurate screening and treatment of HIT in the MCS population.

Clinical decision support to reduce unnecessary diagnostic testing for heparin-induced thrombocytopaenia.

Appropriate evaluation of heparin-induced thrombocytopaenia (HIT) is imperative because of the potentially life-threatening complications. However, overtesting and overdiagnosis of HIT are common. Our goal was to evaluate the impact of clinical decision support (CDS) based on the HIT computerized-risk (HIT-CR) score, designed to reduce unnecessary diagnostic testing. This retrospective observational study evaluated CDS that presented a platelet count versus time graph and 4Ts score calculator to clinicians who initiated a HIT immunoassay order in patients with predicted low risk (HIT-CR score 0-2). The primary outcome was the proportion of immunoassay orders initiated but cancelled after firing of the CDS advisory. Chart reviews were conducted to assess anticoagulation usage, 4Ts scores and the proportion of patients who had HIT. In a 20-week period, 319 CDS advisories were presented to users who initiated potentially unnecessary HIT diagnostic testing. The diagnostic test order was discontinued in 80 (25%) patients. Heparin products were continued in 139 (44%) patients, and alternative anticoagulation was not given to 264 (83%). The negative predictive value of the advisory was 98.8% (95% CI: 97.2-99.5). HIT-CR score-based CDS can reduce unnecessary diagnostic testing for HIT in patients with a low pretest probability of HIT.

Evaluation of a diagnostic test for heparin-induced thrombocytopenia: validation of a delayed test time

Heparin-induced thrombocytopenia (HIT) is a rare, iatrogenic condition, characterized by its potential severity and diagnostic difficulties. The diagnosis is based on a set of arguments allowing the calculation of a pre-test score pointing to HIT. There are rapid diagnostic tests for suspected HIT. Among these, the STic Expert® HIT has a good sensitivity to detect HIT. However, it must be performed within 2 hours after sampling. The aim of this study was to evaluate a delayed STic Expert® HIT test at 8 hours and in frozen plasma. Thirty-six patients were prospectively included for HIT testing between April 01, 2018, and July 1, 2022, at the University Rouen Hospital. For any request for HIT testing, an analysis by STic Expert® HIT was performed within 2 hours and 8 hours post-sampling. Any positive result was confirmed by a functional test, platelet aggregation with heparin, release of 14C-serotonin assay (SRA), and immunological assay by a research for anti-platelet factor 4 IgG antibodies. Twenty-three patients had a STic Expert® HIT. Sixteen presented platelet aggregations in the presence of heparin and had a positive anti-PF4 test, 17 had a positive SRA. Six patients had no HIT. For the test performed within 2 hours of collection, the Se= 100%, Sp= 68.42%, PPV= 73.91%, and NPV= 100%. The X2= 18.21 with p< 0.001. For the test performed at 8 hours post sampling, the Se= 100%, Sp= 68.42%, PPV= 73.91% and NPV= 100%. The X2= 18.21 with p< 0.001. In conclusion, we have demonstrated that the STic Expert® can be used to perform an HIT diagnostic test 8 hours after sampling and on thawed plasma. However, this study needs to be confirmed on a larger number of samples.

Cerebral venous sinus thrombosis associated with SRA-negative heparin-induced thrombocytopenia: case report

BackgroundThere are very few documented reports in literature of cerebral venous sinus thrombosis (CVST) caused by immune-mediated heparin-induced thrombocytopenia (HIT). Further, there are very few reports of false negative serotonin release assays (SRAs) when testing for immune-mediated HIT.Case presentationWe present a case of a 60- year-old male with recent unfractionated heparin administration for venous thromboembolism prophylaxis, an elevated 4T score of 5 and acute CVST in which immune-mediated HIT was suspected. The enzyme-linked immunosorbent assay (ELISA) screening assay was positive for PF4 antibodies and subsequent reflexive SRA testing was negative. However, given the clinical picture, a false-negative SRA was suspected (and eventually confirmed), prompting use of the alternative PF4-dependent p-selectin expression assay (PEA) which was confirmed to be positive. The patient was successfully managed with a bivalirudin infusion and eventually transitioned to apixaban.ConclusionIt is uncommon for immune-mediated HIT with thrombosis to manifest as CVST. Similarly, false-negative SRA is uncommon in immune-mediated HIT. Take-away lessons from our case report include considering HIT in CVST patients with an elevated 4T score and considering the entire clinical picture and degree of suspicion for HIT when interpreting negative HIT testing results. The PEA, in conjunction with the 4Ts score, may be considered as an alternate diagnostic assay for HIT.

Heparin-Induced Thrombocytopenia in Patients Undergoing Venoarterial Extracorporeal Membrane Oxygenation.

Background: Heparin-induced thrombocytopenia (HIT) is a serious, immune-mediated adverse drug reaction to unfractionated heparin (UFH) affecting also patients undergoing venoarterial extracorporeal membrane oxygenation (VA-ECMO). Although the association between VA-ECMO support and the development of thrombocytopenia has long been known and discussed, HIT as one underlying cause is still insufficiently understood. Therefore, the purpose of this study was to further investigate the epidemiology, mortality, diagnosis, and clinical management of HIT occurring in VA-ECMO patients treated with UFH. Methods: We conducted a retrospective single-center study including adult patients (≥18 years) with VA-ECMO support in the cardiac intensive care unit (ICU) of the University Hospital of Munich (LMU) between January 2013 and May 2022, excluding patients with a known history of HIT upon admission. Differences in baseline characteristics and clinical outcome between excluded HIT (positive anti-platelet factor 4 (PF4)/heparin antibody test but negative functional assay) and confirmed HIT (positive anti-PF4/heparin antibody test and positive functional assay) VA-ECMO patients as well as diagnosis and clinical management of HIT were analysed. Results: Among the 373 patients included, anti-PF4/heparin antibodies were detected in 53/373 (14.2%) patients. Functional HIT testing confirmed HIT in 13 cases (3.5%) and excluded HIT in 40 cases (10.7%), corresponding to a prevalence of confirmed HIT of 13/373 (3.5%) [1.6, 5.3] and a positive predictive value (PPV) of 24.5% for the antibody screening test. The platelet course including platelet recovery following argatroban initiation was similar between all groups. One-month mortality in patients with excluded HIT was 14/40 (35%) and 3-month mortality 17/40 (43%), compared to 5/13 (38%) (p > 0.999), and 6/13 (46%) (p > 0.999) in patients with confirmed HIT. Neurological outcome in both groups measured by the cerebral performance category of survivors on hospital discharge was similar, as well as adverse events during VA-ECMO therapy. Conclusions: With a prevalence of 3.5%, HIT is a non-frequent complication in patients on VA-ECMO and was not associated with a higher mortality rate. HIT was ultimately excluded by functional essay in 75% of VA-ECMO patients with clinical suspicion of HIT and positive anti-PF4/heparin antibody test. Argatroban seems to be an appropriate and safe therapeutic option for confirmed HIT-positive patients on VA-ECMO support.

Whole Blood Procoagulant Platelet Flow Cytometry Protocol for Heparin-Induced Thrombocytopenia (HIT) and Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT) Testing.

Heparin-induced thrombocytopenia (HIT) is a well-characterized, iatrogenic complication of heparin anticoagulation with significant morbidity. In contrast, vaccine-induced immune thrombotic thrombocytopenia (VITT) is a recently recognized severe prothrombotic complication of adenoviral vaccines, including the ChAdOx1 nCoV-19 (Vaxzevria, AstraZeneca) and Ad26.COV2.S (Janssen, Johnson & Johnson) vaccines against COVID-19. The diagnosis of HIT and VITT involve laboratory testing for antiplatelet antibodies by immunoassays followed by confirmation by functional assays to detect platelet-activating antibodies. Functional assays are critical to detect pathological antibodies due to the varying sensitivity and specificity of immunoassays. This chapter presents a protocol for a novel whole blood flow cytometry-based assay to detect procoagulant platelets in healthy donor blood in response to plasma from patients suspected of HIT or VITT. A method to identify suitable healthy donors for HIT and VITT testing is also described.

Functional Testing for Heparin-Induced Thrombocytopenia Using Whole Blood Multiplate Impedance Aggregometry.

Immune-mediated heparin-induced thrombocytopenia (HIT) occurs when heparin-dependent IgG antibodies bind to heparin/platelet factor 4 (H/PF4) complexes and activate platelets. There is a vast panoply of assays to investigate HIT which can be divided into two groups, antigen-based immunoassays that detect all antibodies against H/PF4 and are used as a first diagnostic step and functional assays that will identify only the antibodies capable of activating platelets and are mandatory to confirm a diagnosis of pathological HIT. The serotonin-release assay, known as SRA, has been the gold standard for decades, but in the last 10years, other easier alternatives have been described. The current chapter will focus on whole blood multiple electrode aggregometry, a validated method for the functional diagnosis of HIT.

Rethinking the Gold Standard: Real-World Performance of the Serotonin Release Assay (SRA) and PF4-Dependent P-Selectin Expression Assay (PEA) in the Diagnosis of Heparin-Induced Thrombocytopenia (HIT)

Background Heparin-induced thrombocytopenia (HIT) is a complication of heparin exposure with potential for significant morbidity and mortality. The serotonin release assay (SRA) has been considered the gold standard for HIT diagnosis. However, the SRA is technically challenging and results can be influenced by specimen handling and preparation. Therefore, the performance of the real-world assays may differ from published standards but reports of real-world performance are not widely available. A new assay, the PF4-dependent P-selectin expression assay (PEA), has demonstrated comparable accuracy in HIT diagnosis employing a simpler laboratory technique. Herein, we report the real-world performance of a reference laboratory SRA and PEA and describe how incorporation of the PEA into the testing algorithm positively influenced the HIT diagnostic process at a large academic medical center. Methods At the University of Alabama at Birmingham, we incorporated the PEA into HIT testing at provider discretion in patients with inconclusive SRA results starting January 1, 2020. Since July 15, 2020, we solidified the use of PEA in our algorithm (Figure 1) in which all patients with an inconclusive SRA had a PEA on the same specimen. A PEA could also be ordered ad hoc if the SRA result did not correlate with clinical suspicion for HIT. We retrospectively compared patients tested for HIT for 2 years before PEA use (January 1, 2018 to December 31, 2019; pre-PEA period) to the >2 years since using the PEA (January 1, 2020 to March 1, 2022; PEA period). All patients tested with PEA at our institution are included in Table 1. Laboratory testing: Enzyme immunoassay (EIA) was performed at our institution using Asserachrom® HPIA, Diagnostica Stago (France). The SRA and PEA assays were performed at Versiti (Milwaukee, WI). SRA was positive if there was >20% release of serotonin with low dose heparin (0.1 U/mL) and <20% release in with high dose heparin (100 U/mL). An inconclusive result was defined as a percentage of serotonin release not meeting criteria for a positive result (e.g., >20% release of serotonin with both low and high dose heparin, or some release but <20% with low dose along with inhibition with high dose). Statistical analysis Descriptive statistics were employed to examine the sample of patients with an inconclusive SRA result, comparing those with and without PEA testing. Bivariate analyses were conducted to compare testing patterns in the pre-PEA and PEA periods, and T-tests of significance were conducted to analyze assay results. All models were estimated using Stata 17 (StataCorp. 2019. Stata Statistical Software: Release 17. College Station, TX: StataCorp LLC). ResultsSRA results: In the pre-PEA and PEA periods, there were 1,252 and 1,403 EIAs performed, respectively. The rate of EIA positivity was similar in both groups (14% vs 15%, p=0.813). A total of 379 SRAs were sent in both periods, with 24 inconclusive results (6%, 15 pre-PEA and 9 PEA). PEA performance: In the 24 patients with inconclusive SRA results, HIT was diagnosed in 7 of 15 patients (47%) pre-PEA, compared to 3 of 9 patients (33%) in the PEA period. Table 1 presents the details of each case where PEA was used due to diagnostic uncertainty. Of the 9 patients with an inconclusive SRA result in the PEA period, PEA provided a definitive result in 8 cases (89%). In 2 cases, the PEA confirmed the SRA result, 1 positive and 1 negative. In 1 case with a positive SRA and low clinical suspicion, the PEA was negative. Conclusion Evaluation of the real-world performance of the SRA reveals that although inconclusive results are rare (6%), they can present a significant diagnostic challenge in centers with high testing volume. The PEA demonstrated reliable performance in patients with an inconclusive SRA, producing a definitive result in 89% of cases. The percentage of patients diagnosed with HIT after an inconclusive SRA result decreased with incorporation of the PEA (47% to 33%), suggesting that PEA use helped refute a HIT diagnosis when there was clinical uncertainty. Further studies are needed to determine the optimal testing algorithm to produce rapid, reliable HIT diagnosis. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

"Autoimmune HIT", a Potential Diagnostic Artifact Due to Remnant Heparin in HIT Samples, Is Not Associated with More Severe Outcomes

In recent years, there has been increasing use of the term "autoimmune" heparin-induced thrombocytopenia (HIT) to describe patients with HIT antibodies that activate platelets in the absence of exogenous heparin (i.e., the "zero heparin" serotonin release assay, SRA), with the proposed implication that such patients present with more severe phenotypes. Platelet activation in the SRA in the absence of exogenous heparin is likely a real phenomenon in rare/infrequent patients who did not receive proximate heparin therapy (Spontaneous HIT) and in patients who develop HIT after heparin treatment has ceased (delayed-onset HIT). However, in other patients deemed to have "autoimmune" HIT based on reactivity in the "zero heparin" SRA, we hypothesized that platelet reactivity in this SRA test system might result from remnant heparin in the patient's diagnostic blood sample. To further complicate the interpretation of autoimmune HIT testing, there is a lack of rigorous data demonstrating a correlation between this diagnosis and disease severity. This study was undertaken to evaluate the technical validity and clinical relevance of an autoimmune HIT diagnosis. First, thirty "real-world" diagnostic HIT patient samples were subjected to anti-Xa testing. Remarkably, fourteen of the 30 samples (47%) had detectable heparin, with a range of 0.11-0.55 IU/mL for thirteen samples, while one sample had heparin <0.1 IU/mL (data not shown due to Abstract 2-figure panel limit). Next, to determine the extent to which low concentrations of unfractionated or low molecular weight heparin spiked into patient samples impact reactivity in the SRA, spiked samples were tested in the "conventional" low dose heparin (0.1 IU/ml) SRA and the "zero heparin" SRA (autoimmune HIT test). Fig 1A demonstrates that even ultra-low concentrations of unfractionated heparin (0.06 IU/mL) spiked into the sample facilitate serotonin release in the "zero heparin" SRA. On the other hand, the conventional SRA was not impacted by heparin spiked into samples unless concentrations were 5 IU/mL or higher, several-fold greater than what would be seen in patient samples. Similarly, LMWH induced platelet reactivity in the zero heparin SRA at concentrations between 0.25-1.0 IU/mL, while there was no effect on the conventional SRA at these concentrations (data not shown). As proof-of-concept that low levels of heparin mediate reactivity in a zero-heparin functional test, a HIT patient sample devoid of heparin was spiked with 0.05 IU/ml of heparin and evaluated with and without digestion with heparinase I. Heparin-spiked samples induced platelet activation in a zero-heparin functional assay which was abrogated upon heparinase I digestion (data not shown). Together, these results are consistent with the hypothesis that at least some cases of "autoimmune HIT" are labeled as such due to residual heparin present in patient samples rather than due to the presence of a qualitatively different ("autoimmune") HIT antibody. To evaluate the clinical relevance of an "autoimmune" HIT diagnosis, platelet nadir and the presence of thrombosis were interrogated as markers of disease severity in a cohort of 48 HIT patient samples with unknown heparin levels. Thirty-six patients were positive in the zero heparin SRA ("Autoimmune HIT" cohort; >50% serotonin release), while 12 were negative ("Classical HIT" cohort; positive in the conventional SRA, but <50% serotonin release in the zero heparin SRA). Fig 1B demonstrates that there was no difference in platelet nadir between the two groups (p=0.562); further, there were no differences between these groups in rates of confirmed thrombosis/skin necrosis and acute system reactions (p=0.324; data not shown). In summary, "autoimmune HIT" diagnostic testing (zero-heparin SRA) should not be performed until samples are confirmed to be devoid of heparin, and rigorous large-scale studies are needed to evaluate whether results of validly-conducted autoimmune HIT tests correlate with disease severity. Figure 1. (A) Low concentrations of spiked heparin in a HIT patient sample facilitates platelet activation in the "autoimmune" HIT test (zero-heparin SRA; red line) but does not affect the conventional SRA (black line). (B) Platelet nadir was similar between "autoimmune" (n=36) and conventional HIT (n=12) cohorts. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Abstract 11896: Spontaneous Heparin-Induced Thrombocytopenia Presenting as Acute Stent Thromboses Following an Acute St-Segment Elevation Myocardial Infarction

Introduction: Spontaneous heparin-induced thrombocytopenia (HIT) is a rare clinical variant that develops without prior exposure to heparin. We present a 40-year-old man who was diagnosed with spontaneous HIT after an acute ST-segment elevation myocardial infarction complicated by multiple acute stent thromboses and left ventricular (LV) thrombus. Case: A 40-year-old previously healthy man with no known history of heparin exposure presented to our emergency department with an acute ST-segment elevation myocardial infarction. Emergent coronary angiography revealed a severely thrombotic 100% occlusion of his distal left anterior descending artery for which thrombectomy and percutaneous coronary intervention (PCI) were performed with placement of a drug eluting stent. Prior to angiography, the patient received 4000 units of unfractionated heparin and an additional 2000 units intra-arterially during the case. Labs prior to PCI revealed thrombocytopenia and HIT enzyme-linked immunoassay testing was sent. He underwent repeat angiography two additional times during his course for recurrent chest pain which both revealed acute stent thrombosis. HIT testing eventually returned positive for the presence of platelet factor 4 antibodies. A subsequent serotonin release assay returned positive, confirming the diagnosis of HIT. A transthoracic echocardiogram during his hospitalization also revealed an LV thrombus. Discussion: Heparin-induced thrombocytopenia (HIT) is traditionally diagnosed after thrombocytopenia develops 5 to 10 days after exposure to heparin. However, there have been rare reports of a spontaneous form of HIT that can occur without prior exposure to heparin. This case highlights a rare presentation of spontaneous HIT. Although infrequent, cardiologists should be aware of atypical presentations of HIT, since almost all patients will receive heparin prior to or during coronary angiography and coronary interventions. Spontaneous HIT should be considered in all patients who present with unexplained thrombocytopenia with arterial and/or venous thrombi. Failure to recognize this clinical entity could lead to potentially life-threatening thrombotic complications from further administration of heparin.

Application of a clinical decision rule and laboratory assays in pediatrics: Adult heparin-induced thrombocytopenia.

Heparin-induced thrombocytopenia (HIT) is rare among pediatric patients. The diagnosis of HIT depends upon clinical decision tools to assess its pretest probability, supported by laboratory evidence of anti-platelet factor 4 (anti-PF4)/heparin antibodies. To compare the use of the 4Ts score clinical decision tool, clinical characteristics, and laboratory findings between pediatric and adult patients with suspected HIT. We compiled all pediatric patients in our center for whom HIT testing was performed during the years 2015-2021. These were compared with a cohort of consecutive adult patients. Laboratory diagnosis of HIT was performed with particle gel immunoassay (PaGIA) as screening test and confirmed by an automated latex-enhanced immunoturbidimetric assay (LIA) and/or by functional flow cytometry assay (FCA). The cohort included 34 children (under 18years) and 105 adults. Adults mostly received heparins for thromboembolism prophylaxis and treatment (72.4%, n=76), and were more frequently treated with low-molecular-weight heparin (LMWH). Children were mostly exposed during cardiopulmonary bypass and extracorporeal membrane oxygenation (ECMO, 61.8%, n=21), and were more frequently treated with unfractionated heparin (UFH). Compared with adults, children had significantly higher 4Ts scores. Nevertheless, adults had a slightly higher rate of a positive diagnosis of HIT. Six out of 16 adults with confirmed HIT presented with thrombosis (37.5%), whereas all three pediatric patients with HIT presented with thrombosis (p= .087). 4Ts scores are higher in children compared with adult patients for whom laboratory tests for HIT were obtained. A potentially higher incidence of thrombosis in children with HIT may be attributable to the severity of underlying illness.