Heparin-induced Platelet Aggregation Test Research Articles

Proteomic profiling for biomarker discovery in heparin-induced thrombocytopenia

AbstractNew analytical techniques can assess hundreds of proteins simultaneously with high sensitivity, facilitating the observation of their complex interplay and role in disease mechanisms. We hypothesized that proteomic profiling targeting proteins involved in thrombus formation, inflammation, and the immune response would identify potentially new biomarkers for heparin-induced thrombocytopenia (HIT). Four existing panels of the Olink proximity extension assay covering 356 proteins involved in thrombus formation, inflammation, and immune response were applied to randomly selected patients with suspected HIT (confirmed HIT, n = 32; HIT ruled out, n = 38; and positive heparin/platelet factor 4 [H/PF4] antibodies, n = 28). The relative difference in protein concentration was analyzed using a linear regression model adjusted for sex and age. To confirm the test results, soluble P-selectin was determined using enzyme-linked immunosorbent assay (ELISA) in above mentioned patients and an additional second data set (n = 49). HIT was defined as a positive heparin-induced platelet activation assay (washed platelet assay). Among 98 patients of the primary data set, the median 4Ts score was 5 in patients with HIT, 4 in patients with positive H/PF4 antibodies, and 3 in patients without HIT. The median optical density of a polyspecific H/PF4 ELISA were 3.0, 0.9, and 0.3. Soluble P-selectin remained statistically significant after multiple test adjustments. The area under the receiver operating characteristic curve was 0.81 for Olink and 0.8 for ELISA. Future studies shall assess the diagnostic and prognostic value of soluble P-selectin in the management of HIT.

Similarities of antiphospholipid antibodies in HIT and APS patients with heparin-platelet factor 4 antibodies

Heparin-induced thrombocytopenia (HIT) is a prothrombotic autoimmune disorder confirmed by the existence of Heparin-Platelet Factor 4 (HPF4) antibodies. The aim of this work is to study the possible relationship between anti-HPF4 and antiphospholipid antibodies (aPLs) that may explain the discrepancies observed in patients with a suspected HIT (HIT group) with positive immunoassay (HPF4-Elisa) and negative functional assay (heparin-induced platelet aggregation test). So, we performed H-PF4 antibodies research in 31 APS confirmed patients (APL group). All tests performed have been compared to normal controls (n = 34). We found anti-H-PF4 in 7/31 patients of APL group. In parallel, we search for aPLs in 9/34 patients tested positive for anti-HPF4 in HIT group, all of them were positive. All specificities were observed in the two anti-HPF4 positive groups (aβ2GP1 IgM/IgG/IgA, aCL (IgM/IgG/IgA, aPS-PT IgM/IgG). The most associated antibodies with anti-HPF4 are the anti ß2Glycoprotein1 (Odds ratio = 50.1). We suggest that the presence of aPLs in HIT group with anti-HPF4 could be the cause of the discrepancies. In addition, we performed the Heparin Neutralization Assay (HNA) which is specific for anti-HPF4, neutralization was obtained for patients exposed to heparin. Furthermore, we suggest that we should performed a larger cohort to confirm the causal relationship of aPLs and also to expand the tests allowing the differentiation between these autoantibodies.

Accuracy of heparin-induced platelet aggregation test for the diagnosis of heparin-induced thrombocytopenia

IntroductionWhereas the utility of washed platelet assays such as the heparin-induced platelet activation test (HIPA) for the diagnosis of heparin-induced thrombocytopenia (HIT) is regarded as high, the performance of simpler assays such as the heparin-induced platelet aggregation test (PAT) is still elusive. Using well-characterized samples of a large cohort study, we aimed to assess the diagnostic accuracy of PAT for the diagnosis of HIT. Material and methodsOne-hundred twenty-two immunoassay-positive serum samples of a previous, prospective single-center cohort study including consecutive patients with suspected HIT (n = 1291) were used. HIPA was determined as reference gold standard; samples were previously analyzed using PAT as well as polyspecific platelet factor 4/heparin enzyme-linked immunosorbent assay (ELISA). 4Ts score was calculated using the patient documentation. Diagnosis of HIT was defined as a positive HIPA, which is a positive reaction in 2 out of 4 donor platelets within 30 min. ResultsHIT was diagnosed in 39 out of 122 patients corresponding to a prevalence of 32%. Median optical density (ELISA) was 2.8 (inter-quartile range 2.3, 3.0) in patients with HIT and 0.7 (0.5, 1.3) in patients without HIT. PAT was positive in 27 out of 39 HIT patients and it was negative in 83 out of 83 HIT-negative patients. Thus, the sensitivity of PAT for the diagnosis of HIT was 69% (95% confidence interval 52%, 83%) and the specificity 100% (96%, 100%). ConclusionsOur results demonstrate that PAT is a valuable test to confirm HIT but cannot be applied to rule-out HIT in clinical practice.

Heparin-induced thrombocytopaenia diagnostic testing after adult cardiac surgery: a single-centre experience and development.

To assess the incidence and outcome of heparin-induced thrombocytopaenia (HIT) in patients after cardiac surgery on cardiopulmonary bypass (CPB) and to review the time course of platelet counts and the use of different immunological diagnostic tests. All patients ≥18 years of age who underwent CPB from 2006 to 2015 and who were postoperatively admitted to our cardiac intensive care unit (ICU) were included in this retrospective study. Screening for heparin/platelet factor-4 antibodies was performed using an antibody test, which was later replaced with a screening test specific for IgG antibodies without IgA/IgM cross-reactivity. The enzyme immunoassay (EIA) for the detection of antibodies of all immunoglobulin classes against heparin/PF4 complexes was replaced with an IgG-specific EIA. HIT was confirmed by a heparin-induced platelet aggregation test until 2014. Among 4978 patients admitted between 2006 and 2015, 539 (11%) patients were evaluated for HIT. Patients were excluded because of age <18 years (n = 9), non-cardiac surgery without CPB (n = 10) or incomplete data (n = 3). Of the remaining 517 patients, 43 (8.3%) patients were HIT-positive. HIT incidence was 0.86%. The proportion of HIT-positive patients was similar in men and women (8.4% and 8.2%, respectively). Men and women with suspected HIT also had similar in-hospital mortality (odds ratio ≈ 1; P = 0.926). The incidence of HIT was lower in our study than previously reported. Novel immunological tests have improved to specifically detect IgG antibodies. Furthermore, they are able to detect anti-protamine antibodies, which may be present in patients with high clinical probability of testing negative for HIT. Incidence and clinical relevance of heparin/protamine antibodies will be subjects of future investigation.

Evaluation of STic Expert® HIT Kit and Its Comparison with ID-PaGIA™ Test in Suspected Heparin-Induced Thrombocytopenia.

Heparin-induced thrombocytopenia (HIT) is an adverse drug reaction caused by heparin. HIT occurs due to IgG antibodies directed against heparin-bound platelet factor 4 (PF4). The aim of this study was to evaluate the STic® Expert HIT for detection of anti-PF4/heparin antibodies in comparison with ID-PaGIA™ kit. The results were further confirmed by Heparin-induced platelet aggregation test (HIPA). A total of 17 patients with a suspected diagnosis of HIT were enrolled. The 4T scoring of each case was performed. Testing for HIT was carried out by ID-PaGIA™, STic® Expert HIT, and HIPA. Testing by STic® Expert HIT test demonstrated positivity in three cases while testing by ID-PaGIA™ test kit revealed four positive cases. Two of these cases were confirmed as HIT by HIPA. The study suggests that STic® Expert HIT an equally effective test, in combination with the 4T scoring system for detecting/excluding the diagnosis of HIT. A large number of cases are needed for validation.

Idiopathic catastrophic thrombosis with happy ending

A 59-year-old male patient suffered three life-threatening instent thromboses after an initial resuscitation due to an ST-segment elevation myocardial infarction of the anterior cardiac wall. With a high-risk profile for...

Rapid immunoassays for diagnosis of heparin-induced thrombocytopenia: Comparison of diagnostic accuracy, reproducibility, and costs in clinical practice.

BackgroundImmunoassays are crucial in the work-up of patients with suspected heparin-induced thrombocytopenia (HIT) and rapid tests have been recently developed. However, comparative data on diagnostic accuracy, reproducibility, and analytical costs of different immunoassays in clinical practice are limited.MethodsSamples of 179 consecutive patients evaluated for suspected HIT in clinical practice using a polyspecific enzyme-linked immunoabsorbent assay (GTI diagnostics; ELISA) and a rapid particle gel immunoassay (PaGIA), were additionally analysed with a IgG-specific chemiluminescent immunoassay (AcuStar HIT-IgG). Presence of HIT was defined as a positive functional heparin-induced platelet aggregation test. Diagnostic accuracy was determined for low, intermediate and high thresholds as previously established (ELISA: optical density 0.4, 1.3, and 2.0 respectively; PaGIA: positive/negative, titre of 4, titre of 32; AcuStar HIT-IgG: 1.0 U/ml, 2.8, 9.4) and reproducibility was assessed by repeated measurements. Costs of test determination were calculated taking reagents, controls, and working time of technicians according to Swiss health care system into account.ResultsData on PaGIA results were available for 171 patients (95.5%), ELISA for 144 patients (80.4%), and AcuStar HIT-IgG for 179 patients (100%). Sensitivity was above 95% for all assays at low and intermediate thresholds. Specificity increased with higher thresholds and was above 90% for all assays with intermediate and high thresholds. Specificity of AcuStar HIT-IgG (92.8%; 95% CI 87.7, 96.2) was significantly higher than PaGIA (83.0%; 95% CI 76.3, 88.5) and higher than ELISA (81.8%, 95% CI 74.2, 88.0) at low threshold (p<0.05). Reproducibility was adequate for all assays. Total costs per test were CHF 51.02 for ELISA, 117.70 for AcuStar HIT-IgG, and 83.13 for PaGIA.ConclusionsWe observed favourable diagnostic accuracy measures and a high reproducibility for PaGIA and AcuStar HIT-IgG. Implementation into 24-hours-service might improve patient care but the results must be confirmed in other settings and larger populations as well.

Diagnostic dilemma of post bypass thrombocytopenia – A case report

Various causes are attributed to postoperative thrombocytopenia in a patient who has undergone cardiac bypass. The incidence of heparin-induced thrombocytopenia (HIT) in Indians is 5.6%. We present here 2 cases of postcoronary artery bypass graft surgery; both were presenting with >50% drop in platelets on day 5 of heparin injection, both had acute kidney injury, and one also had transaminitis. The detection of anti-heparin PF4 antibodies was performed by rapid ID Micro-gel typing system in both the cases and one was confirmed as HIT.Heparin/PF4 Antibody card test and heparin-induced platelet aggregation test (PAT) other was negative and was finally diagnosed as disseminated intravascular coagulation. Thus rapid diagnosis was reached and patients were managed accordingly, which is different in both conditions.

Argatroban as an Alternative Anticoagulant in the Case of Heparin-Induced Thrombocytopenia after Pediatric Cardiac Surgery

Heparin-induced thrombocytopenia (HIT) represents a major challenge in patients following the fenestrated Fontan procedure. These patients are prone to thrombosis within the Fontan tunnel due to the low blood flow velocity. The communication between the Fontan tunnel and the common atrium may enable systemic embolization and can cause a stroke. Effective on-going anticoagulation is necessary. Given the high risk of arterial and venous thrombosis with HIT, alternate anticoagulation management is essential as soon as HIT is suspected. We are reporting on two patients who developed HIT antibodies and thrombocytopenia after exposure to heparin during a Fontan procedure. Both the PF4 enzyme-linked immunosorbent assay (LIFECODES® PF4 IgG assay) and the heparin-induced platelet aggregation test (HIPA, Institut fur Immunologie und Transfusionsmedizin, Greifswald, Germany) were positive. The children were treated with argatroban (Argatra®, Mitsubishi Pharma), a direct thrombin inhibitor. In only one patient was HIT associated with thrombosis within the Fontan tunnel.

Heparin: induced thrombocytopenia: incidence and laboratory approach to diagnosis in Indians.

One of the most common complications of heparin administration is heparin-induced thrombocytopenia (HIT) which can also lead to catastrophic thrombotic events. The problem of identifying the cause of thrombocytopenia, as due to heparin, in patients with multiple co-morbid conditions is very essential for management. Thus, the laboratory investigations for diagnosis of HIT play a pivotal role. The objective of the study was to arrive at the incidence of HIT in ethnic Indian population and provide a decision after analysis of tests used to diagnose HIT. 125 consecutive patients (Power of study being 80%) undergoing open heart surgery and receiving unfractionated heparin were taken as subjects. Blood samples were collected a day before the surgery and days 1, 3, 5 and 7 after surgery. The cases were categorized into probable and unlikely groups depending on the clinical presentation and degree fall of platelet count. Anti-heparin PF4-associated antibodies were detected using rapid-ID gel microtyping system and ELISA tests. HIT was also tested using functional assays: heparin-induced platelet aggregation test (PAT) and the rapid luminographic assay of heparin-induced ATP release. Of the 125 patients, 11 patients were clinically labeled as probable HIT and 29 patients were clinically labeled as unlikely HIT. There were seven confirmed cases of HIT cases that were positive for one functional and one immunological assay. Only one case of HITT was encountered. Accordingly, the incidence of HIT was found to be 5.6% and that of HITT to be 0.8%. ELISA tests were positive in 21 cases (17%) which demonstrated the presence of anti-HPF4 antibodies in non-HIT cases as well. It was found that the rapid gel test had sensitivity comparable to functional assay with better specificity than ELISA. Incidence of HIT in ethnic Indian population is 5.6%. Patients with a drop of >50% in platelet count should be perused as a likely candidate of HIT. These cases should be subjected to the ID-HPF4 antibody assay as this is a rapid test, can be done for individual cases, and has better specificity and similar sensitivity than ELSIA. Cases with clinically probable HIT and a positive ID-HPF4 assay can be taken as confirmed cases of HIT. However, cases clinically unlikely for HIT and a positive ID-HPF4 assay should be subjected to another test to establish the diagnosis of HIT.

Early Management of Heparin-Induced Thrombocytopenia Using a Simple Scoring System

Abstract 4679Since stopping heparin therapy lessens the probability of severe complications of heparin-induced thrombocytopenia (HIT) such as arterial and venous thromboembolism, it is important to stop heparin as soon as the diagnosis is suspected. As HIT is a complex disorder and its diagnosis is difficult, the use of a clinical scoring system would facilitate clinical decision making. One of the foremost issues in these patients is whether to discontinue heparin (to avoid HIT complications) or not (to avoid thrombotic complications). This study was performed to develop a simple scoring system to aid in the early clinical management of suspected HIT patients with regard to decisions for continued heparin therapy. The system was designed to arrive at low (0) or possible (1) probability scores based on clinical criteria without knowledge of lab test results, except platelet counts, to avoid delays. As the safest clinical approach is to discontinue heparin, intermediate and high scores were combined. Historically, laboratory tests such as the heparin-induced platelet aggregation test (PA) and 14C-serotonin release assay (SRA) and nonfunctional tests such as the enzyme-linked-immunosorbent assay (ELISA) have been used for the diagnosis of HIT. These test results are frequently available only after 12 to 36 hours which, for some patients, is a risk due to continued heparin therapy while waiting for test results. One solution to this problem is to have a clinical scoring system to guide the clinician before test results are available. This study enrolled 100 critically ill VA hospitalized patients with a >=30% fall in platelet count. Assessment of platelet aggregation (PA), 14C-SRA and GTI ELISA was also performed. In this population 53% were scored 1 and of these 43% were positive by lab testing for HIT. Emphasizing the decision to discontinue heparin, the clinical signs of HIT were paramount for the immediate determination of a diagnosis of HIT. Specifically, this study demonstrated the value of a simple clinical score to aid in the clinical management decision making to continue or discontinue heparin in patients suspected of having HIT, without dependence on a positive HIT lab test. An algorithm is provided. This scoring system does not preclude reassessment of patients in terms of continuing heparin if subsequent laboratory tests and/or thrombosis become positive. Disclosures:No relevant conflicts of interest to declare.

Rapid exclusion or confirmation of heparin-induced thrombocytopenia: a single-center experience with 1,291 patients

The current gold-standard for diagnosing heparin-induced thrombocytopenia is the detection of platelet-activating antibodies by means of functional assays which, since they are time consuming and not widely available, are not suited to guiding acute treatment decisions. The objective of our study was to assess the ability of more rapid immunoassays to predict the presence of functionally relevant anti-platelet factor 4/heparin-antibodies. We analyzed 1,291 of 1,383 (93.4%) patients consecutively evaluated for suspected heparin-induced thrombocytopenia at our institution. Clinical pre-test probability was defined by the 4T-score. Anti-platelet factor 4/heparin-antibodies were measured with three immunoassays (ID-H/PF4-PaGIA, Asserachrom-HPIA, and GTI-PF4) and their functional relevance was assessed by a two-point heparin-induced platelet aggregation test. Performance of the immunoassays was evaluated by receiver operating characteristic analysis. Among 1,291 patients, 96 (7.4%) had a positive heparin-induced platelet aggregation-test: 7 of 859 (0.8%) with a low, 50 of 358 (14.0%) with an intermediate, and 39 of 74 (52.7%) with a high 4T-score. Receiver operating characteristics analysis indicated that best immunoassay thresholds for predicting a positive platelet aggregation test were: Titer of 4 or more (ID-H/PF4-PaGIA), optical density more than 0.943 (Asserachrom-HPIA) and more than 1.367 (GTI-PF4). A 100% negative predictive value was observed at the following thresholds: Titer of 1 or under (ID-H/PF4-PaGIA), optical density less than 0.300 (Asserachrom-HPIA) and less than 0.870 (GTI-PF4). A 100% positive predictive value was reached only by ID-H/PF4-PaGIA, at titers of 32 or over. Positive and negative likelihood ratios were calculated for results between the thresholds with 100% negative or positive predictive value. We show that: i) negative and weak positive results of immunoassays detecting anti-platelet factor 4/heparin-antibodies exclude heparin-induced thrombocytopenia; ii) anti-platelet factor 4/heparin-antibody titers of 32 or over (ID-H/PF4-PaGIA) have a 100% positive predictive value for functionally relevant antibodies; iii) combining the clinical pre-test probability with the likelihood ratio of intermediate immunoassay results allows assessment of post-test probability for heparin-induced thrombocytopenia in individual patients.

Heparin-Induced Thrombocytopenia After Liver Transplantation

Backgound Unfractionated heparin sodium (UFH) or low–molecular weight heparin (LMWH) is used in anticoagulant protocols at several institutions to prevent thrombosis after liver transplantation. Heparin-induced thrombocytopenia (HIT) is an adverse immune-mediated reaction to heparin, resulting in platelet count decreases of more than 50%. The frequencies of HIT after liver transplantation and platelet factor 4/heparin-reactive antibody (HIT antibody) positivity in liver transplantation patients, however, are unknown. Patients and Methods The 32 men and 20 women underwent living donor liver transplantation. We started LMWH (25 IU/kg/h) on postoperative day (POD) 1, switching to UFH (5000 U/d) on POD 2 or 3. The dose of UFH was changed according to the activated clotting time level. HIT antibody levels were measured the day before surgery and on POD 7 and 14. Platelet count was measured daily for 3 weeks. Results The average platelet counts preoperatively, and on POD 7, 14, and 21 were 65, 88, 149, and 169 × 10 9/L, respectively. Two patients developed hepatic artery thrombosis on POD 11 and 19, respectively, although they were HIT antibody–negative and their platelet counts were stable. In 2 other patients, the platelet count decreased suddenly from 107 × 10 9/L on POD 4 to 65 × 10 9/L on POD 6 and from 76 × 10 9/L on POD 7 to 33 × 10 9/L on POD 9, respectively. The heparin-induced platelet aggregation test was negative in these patients. The percentage of HIT antibody–positive patients was 0.5% preoperatively, 5.6% on POD 7, and 5.6% on POD 14. None of the subjects/patients developed UFH-related HIT. Conclusions In our series, the occurrence of HIT after liver transplantation was uncommon.

Laboratory diagnosis of heparin-induced thrombocytopenia in Asian Indians as investigated with functional and immunologic methods.

Heparin-induced thrombocytopenia (HIT) was looked for in 33 Indian patients undergoing cardiovascular surgery who received unfractionated heparin (UFH). Platelet counts were performed before the initiation of UFH therapy and 5 to 16 days after administration of the therapy. A decrease in patients' platelet count > 35% of the baseline value or < 100,000/microL was considered to be suggestive of HIT syndrome. Heparin-induced platelet aggregation (HIPA) and enzyme-linked immunosorbent assay (ELISA) tests were performed in all the patients to detect antibodies against heparin/PF4 complex. Thrombocytopenia was found to be present in 10 (30%) patients. Of these, two patients were found to be positive as detected by HIPA and ELISA tests. These two patients were considered to have classic HIT syndrome. One of these had bleeding while the other was asymptomatic. Among the 23 non-thrombocytopenic patients and controls, HIT antibodies were not detectable by HIPA test in all but absent by ELISA in only 21 of them. Two of 23 non-thrombocytopenic patients had positive results on the ELISA test. Because the latter had negative test results on HIPA, they were considered to be false-positive results. Thus, HIT syndrome develops in approximately 6% of Indian patients treated with UFH.

Heparin-induced thrombocytopenia with thrombosis: Incidence, analysis of risk factors, and clinical outcomes in 108 consecutive patients treated at a single institution

Heparin-induced thrombocytopenia with thrombosis (HITT) can lead to serious morbidity and may be potentially fatal. We reviewed our experience with this entity over a 4-year period, to determine the following: 1) incidence and type of thrombosis in patients with heparin-induced thrombocytopenia (HIT), 2) clinical consequences of thrombosis, i.e., amputation, cerebrovascular accidents and death, 3) risk factors associated with development of thrombosis, and 4) impact of therapy on clinical outcomes in patients with HITT. Between 1991-1994, 108 patients were diagnosed to have HIT by heparin-induced platelet aggregation test. Thirty-two (29%) of these developed thrombotic complications, of which 20 were venous, 8 arterial, and 4 both. Five of the 32 died, 3 underwent amputations, and 3 had cerebrovascular accidents. The patients who developed thrombotic complications, when compared to those with HIT alone, were older (68.7 +/- 11.5 vs. 63.3 +/- 16 years, P = .05), had more severe thrombocytopenia (platelet count 46,300 +/- 30,400/mm3 vs. 62,500 +/- 34,400/mm3, P = .02), and developed it earlier (6.0 +/- 2.9 vs. 7.4 +/- 3.1 days, P = .03). Multivariate analysis showed that severity of thrombocytopenia and early fall in platelet count were independent risk factors for development of thrombotic complications. We did not find an association between development of thrombosis and clinical events (myocardial infarction, cardiac procedures or surgery, noncardiac surgery, and sepsis) that occurred immediately prior to onset of thrombocytopenia. Heparin was stopped in all 32 patients with HITT. Six received no additional therapy, and one received a single dose of aspirin. Three of these 7 died. The other 25 received anticoagulant or multiagent therapy, with 2 deaths. The death rate was lower in those who were treated with anticoagulant or multiagent therapy (P = .05). We conclude that: 1) Thrombotic complications occur in about 29% of hospitalized patients who develop HIT. 2) Early, severe fall in platelet count in elderly patients receiving heparin appears to be associated with development of thrombotic complications. 3) Our data do not show an association between development of thrombotic complications and clinical events immediately preceding the diagnosis of HIT. 4) In addition to discontinuation of heparin, anticoagulant or thrombolytic therapy should be considered in patients with HITT.

Diagnostic and therapeutic strategies of white clot syndrome

This study describes our experience with 12 patients with white clot syndrome encountered during a recent 36-month period. The diagnosis was based on the following criteria: (1) development of thrombocytopenia of less than 100,000/mm 3 during administration of heparin therapy, (2) normalization of the platelet count after an interruption in heparin therapy, (3) exclusion of other causes of thrombocytopenia, (4) a positive heparin-induced platelet aggregation test, (5) detection of white clots on pathologic examination, and (6) the presence of thrombotic complications. Of 2,500 patients who received heparin therapy, 12 (0.48%) developed white clot syndrome. Various indications, routes of administration, and types of heparin were implicated. The mean platelet nadir was 26,900/mm 3, and the mean time to onset of heparin-induced thrombocytopenia was 5 days. Thrombotic complications included arterial occlusions of the legs in 11 patients, deep vein thrombosis of the legs in 9 patients (4 had pulmonary embolism), and combined arterial and venous thrombosis in 8 patients. Treatment strategies included discontinuation of heparin in all patients and intravenous infusion of dextran, followed by arterial thrombectomy in four patients, urokinase therapy in two patients for arterial complications, and insertion of Greenfield filters in six patients. All patients were given warfarin. The mortality rate was 25% and the morbidity rate was 50%. An initial platelet count should be obtained on all patients prior to receiving heparin, followed by repeat platelet counts every 2 to 3 days. Once thrombocytopenia or thrombosis is diagnosed, heparin should be discontinued and other methods of therapy considered.