Measurement Of ADAMTS13 Activity Research Articles

ADAMTS13 in the New Era of TTP.

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening, often immune-mediated disease that affects 2-13 persons per million per year. Hemolytic anemia, thrombocytopenia, and end-organ damage due to the formation of microthrombi are characteristic of TTP. ADAMTS13 is a disintegrin, metalloproteinase, cleaving protein of von Willebrand factor (VWF) that processes the VWF multimers to prevent them from interacting with platelets and, in turn, to microvascular thrombosis. Prompt diagnosis of TTP is critical yet challenging. Thrombotic microangiopathies have similar clinical presentation. Measurement of ADAMTS13 activity helps in the differential diagnosis. Less than 10% ADAMTS13 activity is indicative of TTP. Laboratory ADAMTS13 activity assays include incubating the test plasma with the substrate (full-length VWM multimers) and detection with direct or indirect measurement of the cleavage product. The purpose of this study is to examine the diagnostic potential, advantages, and weaknesses of the ADAMTS13 potency in TTP.

Managing surgical relapse risk in acquired thrombotic thrombocytopenic purpura: a systematic review

•Thrombotic thrombocytopenic purpura (TTP) may relapse after surgery.•In a systematic review, we assessed preoperative TTP prophylaxis.•Pre-emptive ADAMTS-13 activity measurement prior to surgery may improve relapse risk.•Preoperative TTP prophylaxis may lower surgical relapse risk.

Le PTT, une microangiopathie thrombotique de l’hémostase

AbstractThrombotic thrombocytopenic purpura is characterized by a severe deficiency in ADAMTS13 (A disintegrin and metalloprotease with a thromboSpondin type 1 repeats, member 13) activity, lower than 10%. This disease involves Von Willebrand Factor (VWF), which is not cleaved by ADAMTS13. Deficiency is mainly acquired, due to anti-ADAMTS1 3 antibodies (iPTT). Mechanical haemolytic anemia, thrombocytopenia due to consumption and thrombosis in microvessels are observed. The diagnosis should be quickly discussed and confirmed by the measurement of ADAMTS13 activity. Pending the results of this marker, clinicians can use scores with high positive predictive values, which help them rapidly introduce replacement therapies, given the poor prognosis of TTP in the absence of treatment. Caplacizumab is also used as a first-line treatment to limit the formation of microthrombi, pending the efficacy of immunosuppressive treatments started at the same time. Specialized management and long-term follow-up of patients is crucial to evaluate sequelae and to predict relapses.

A Real-World Analysis of Immune Thrombotic Thrombocytopenic Purpura: Comparing Clinical Outcomes of Conventional Treatment Vs Addition of Caplacizumab, a Single-Center Experience

Introduction Immune thrombotic thrombocytopenic purpura (iTTP) is a rare and life-threatening thrombotic microangiopathy that causes systemic platelet-rich microthrombi with multiorgan damage. Caplacizumab is an anti-von Willebrand factor humanized nano-antibody, thereby blocking platelet binding and it is the first targeted therapy approved for the treatment of iTTP, in conjunction with plasma exchange (PLEX) and immunosuppression. Two pivotal randomized controlled trials have provided positive results where the use of Caplacizumab is associated with faster platelet count recovery, decrease relapse rates significantly and reduce mortality and recurrence rates compared with placebo. Likewise, published real-life studies support the positive results; however, today the controversy continues to exist whether Caplacizumab should be used first line or in refractory or relapsed disease. Methods We performed a single-center retrospective, observational analysis of clinic-biological and survival outcomes of conventional treatment alone vs addition of Caplacizumab in adult patients (≥18 years old) with confirmed diagnosis by ADAMTS13 activity of acquired iTTP (first or relapsed episode) who were treated at our institution between April 2008 and June 2023. Baseline demographic and clinical data and laboratory values were collected at the time of diagnosis. The PLASMIC score was determined retrospectively. Day 0 was defined as the day of diagnosis as indicated by the treating physician, beginning of iTTP-specific therapy, or a reported ADAMTS13 activity measurement of less than 10%. Time to normalization of platelet count after the start of iTTP-specific treatment was defined as the first day with a count ≥150×10 9/L (clinical response). Clinical remission, exacerbation, refractory disease, and relapse were defined according to the criteria published by Cuker et al in 2021 for the International Working Group for TTP. Results Patient characteristics, initial disease presentation, treatment modalities, individual courses, and outcome data are shown in Tables 1 and 2. Thirty-three patients were included, 24 received conventional treatment and 9 additional Caplacizumab. In 39.4% of the cases (13 of 33 episodes), iTTP was presented with a disease relapse. An initial ADAMTS13 activity of <10% was reported in all patients of Caplacizumab group (median 0%; range, 0-7%); in the conventional treatment group, in 6 patients the ADAMTS13 activity was not available at diagnosis for data consultation, in the rest of the group, ADAMTS13 activity was <10% in all cases (median 0,3%; range, 0-9%). The median initial thrombocyte count was 12×10 9/L (range, 4-161). Troponin levels were measured in 14 patients (42,4%) at the time of diagnosis; 10 of 14 patients (71,4%) showed increased levels suggesting concomitant myocardial damage. Due to the severity of symptoms 8 of 33 patients (24.2%), were initially treated on intensive care units. Patients were discharged from the hospital after 15 days (range, 4-75). Thirty-two patients (96.9%) received glucocorticoids and PEX, with a median of 8 PEX treatments (range, 2-59), only one patient did not receive any treatment due to death in the first hours after hospital admission, with significant neurological and cardiac involvement. Caplacizumab treatment was started with a median of 1 day after diagnosis (range, 0-12) and the drug was used as a frontline agent in 7 of 9 patients (77.8%). Twenty-four patients (72,7%) were treated with rituximab. Ten patients received additional immunosuppressants. Platelet counts normalized to above 150×10 9/L in a median of 9 days (range, 3-30) in the conventional treatment group versus 5 days (range; 2-57) in the Caplacizumab group ( p=0.243). Clinical remission was achieved in 31 patients. Two patients, died of iTTP complications after achieve clinical response. No differences were observed in the median time to relapse between patients treated with conventional treatment vs additional Caplacizumab (Figure 1). Conclusions In our experience, the use of Caplacizumab improves the clinical response rate, achieves faster platelet count recovery, and decreases relapse; another benefit is an important alleviation in the burden of care, by reducing the number of PEX sessions to achieve remission, as well as a reduction in hospital stay, although not significantly, probably limited by the number of patients included in the study.

A-154 Cost-effectiveness of On-site Vs Send-out Measurement of ADAMTS13 Activity in the Management of Acquired Thrombotic Thrombocytopenic Purpura

Abstract Background Thrombotic thrombocytopenic purpura (TTP) is a rare thrombotic microangiopathy (TMA) caused by congenital or acquired severe deficiency of disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS-13), an enzyme cleaving von Willebrand factor (VWF). ADAMTS-13 deficiency leads to the accumulation of ultra-large VWF multimers, and subsequent platelet aggregation and microthrombi formation. Aside clinical symptoms, the diagnosis of TTP is based thrombocytopenia, hemolytic anemia with the presence of schistocytes, and severely reduced activity of ADAMTS-13 (<10%). As TTP is a life-threatening condition, it is of great importance to shorten the time to the treatment, and according to the French recommendations, the triplet therapy including plasma exchange (PEX), rituximab, caplacizumab, plus corticosteroids, must be administered to patients with suspected TTP until the results of ADAMTS-13 was obtained, and be pursued only in the case of deficiency. Therefore, a rapid ADAMTS-13 testing is critical for early diagnosis and optimal management of acute TTP. Methods We compared the cost-effectiveness of a strategy based on on-site measurement of ADAMTS-13 activity using a rapid fully automated chemiluminescent assay (HemosIL AcuStar ADAMTS-13) vs its centralized measurement in a reference laboratory, as it is currently the case at our institution. For that purpose, we created two scenarios based on either its local measurement with a maximum time-to-result of 16 h (assay performed during daytime, 7/7) or its centralized measurement with a median time-to-result of 4 days (range: 2–8, as demonstrated from the 2018–2021 estimates). The triplet therapy was hypothesized to be started on admission and stopped if ADAMTS-13 activity was >10%. In case of ADAMTS-13 activity <10%, an inhibitor screening would be performed at the reference laboratory, as this assay was not expected to be locally implemented. For the calculation, we considered the costs of reagent, shipping/handling of samples to the reference laboratory, laboratory staff workload, reimbursement rates, and treatments administered in patients with suspected TTP until availability of the ADAMTS-13 result. Results Based on 2018 to 2021 estimates, there was a mean of 60 prescriptions of ADAMTS-13 activity per year. Most were for the follow-up of TTP patients and for patients with non-TTP TMA. Only seven were for the diagnosis of acute TTP, as suggested by the French score, which was confirmed in four cases (mean values). The local measurement of ADAMTS-13 activity was found to be cost-effective with a 16%-reduction of the costs compared to its centralized measurement in those seven patients with suspected TTP during the first 4 days. Conclusion Together with its short turnaround time (33 min) and its full automation, our results suggest that the HemosIL AcuStar ADAMTS-13 activity assay could be an assay of choice to rapidly measure ADAMTS-13 activity in the plasma and thus to establish the diagnosis of acute TTP in emergency settings. Considering the local costs, using the strategy based on the local evaluation of ADAMTS-13 activity led to a 16%-reduction of the overall costs during the first 4 days after admission of the seven patients with suspected acute TTP.

Measuring ADAMTS-13 activity to diagnose thrombotic thrombocytopenic purpura: a novel, fast fiber-optic surface plasmon resonance immunoassay

BackgroundThrombotic thrombocytopenic purpura (TTP) is characterized by severe ADAMTS-13 activity deficiency (<10%). Diagnostic testing is challenging because of unavailability, high cost, and expert technician requirement of ADAMTS-13 enzyme assays. Cost-effective, automated fiber-optic surface plasmon resonance (FO-SPR) platforms show potential for developing diagnostic tests. Yet, FO-SPR has never been explored to measure enzymatic activities. ObjectivesTo develop an easy-to-use ADAMTS-13 activity assay utilizing optical fibers to rapidly diagnose TTP. MethodsThe ADAMTS-13 activity assay was designed and optimized using FO-SPR technology based on a previously described enzyme-linked immunosorbent assay setup. A calibration curve was generated to quantify ADAMTS-13 activity in plasma of healthy donors and patients with acute immune-mediated TTP (iTTP), hemolytic uremic syndrome, or sepsis. ADAMTS-13 activity data from FO-SPR and fluorescence resonance energy transfer-based strategies (FRETS)-VWF73 reference assays were compared. ResultsAfter initial assay development, optimization improved read-out magnitude and signal-to-noise ratio and reduced variation. Further characterization demonstrated a detection limit (6.8%) and inter-assay variation (Coefficient of variation, 7.2%) that showed good analytical sensitivity and repeatability. From diverse plasma samples, only plasma from patients with acute iTTP showed ADAMTS-13 activities below 10%. Strong Pearson correlation (r = 0.854) between FO-SPR and reference FRETS-VWF73 assays were observed for all measured samples. ConclusionsA fast ADAMTS-13 activity assay was designed onto automated FO-SPR technology. Optimization resulted in sensitive ADAMTS-13 activity measurements with a detection limit enabling clinical diagnosis of TTP within 3 hours. The FO-SPR assay proved strong correlation with the reference FRETS-VWF73 assay. For the first time, this assay demonstrated the capacity of FO-SPR technology to measure enzymatic activity in pre-clinical context.

The Combination of the Lactate Dehydrogenase/Hemoglobin Ratio with the PLASMIC Score Facilitates Differentiation of TTP from Septic DIC Without Identification of Schistocytes.

In some cases, differentiating thrombotic thrombocytopenic purpura (TTP) from septic disseminated intravascular coagulation (DIC) without measuring ADAMTS13 activity is critical for urgent lifesaving plasma exchange. To investigate whether PLASMIC score without identifying the presence of schistocytes, D-dimer, fibrin/fibrinogen degradation products (FDP), FDP/D-dimer ratio, prothrombin time-international normalized ratio (PT-INR), lactate dehydrogenase (LD), hemoglobin (Hb), and LD/Hb ratio are useful in differentiating patients with TTP from those with septic DIC. Retrospective analysis was conducted on the medical records of the patients with septic DIC (32 patients) or TTP (16 patients). The PLASMIC score and other laboratory measurements all were helpful in differentiating TTP from septic DIC. When dichotomized between high risk (scores 6-7) and intermediate-low risk (scores 0-5), the PLASMIC score predicted TTP with a sensitivity of 75.0% and a specificity of 100%. However, 4 of 16 patients with TTP and 19 of 32 patients with septic DIC showed comparable PLASMIC scores of 4 or 5, making it difficult to distinguish between the two by PLASMIC score alone. Among the measurements examined, the LDH/Hb ratio was the most useful for differentiation. Receiver operating characteristic analysis of the LD/Hb ratio for predicting TTP revealed a cutoff of 53.7 (IU/10 g) (sensitivity 0.94, specificity 0.91). If the LD/Hb ratio was less than 53.7, it was unlikely that the patient had TTP. A combination of the LD/Hb ratio and the PLASMIC score may be useful for distinguishing between TTP and DIC and identifying patients who need rapid plasma exchange or caplacizumab administration.

ADAMTS13 Activity Measurement by ELISA and Fluorescence Resonance Energy Transfer Assay.

Accurate estimation of ADAMTS13 (a disintegrin-like and metalloprotease with thrombospondin type 1 motif, member 13) activity level is crucial in the diagnostic setting of differentiation between thrombotic thrombocytopenic purpura (TTP) and other thrombotic microangiopathies. The original assays were too cumbersome and time-consuming for use in the acute situation, and treatment was often based on clinical findings alone, with confirmatory laboratory assays following days or weeks later. Rapid assays are now available that can generate results fast enough to impact on immediate diagnosis and management. Assays based on fluorescence resonance energy transfer (FRET) or chemiluminescence principles can generate results in less than an hour, although they require specific analytical platforms. Enzyme-linked immunosorbent assays (ELISA) can generate results in about 4h, but do not require specialized equipment beyond ELISA plate readers that are in regular use in many laboratories. The present chapter describes principles, performance, and practical aspects of an ELISA and a FRET assay, for quantitative measurement of ADAMTS13 activity in plasma.

Rapid Diagnosis of Acute Thrombotic Thrombocytopenic Purpura (TTP) Using a New Fully Automated Chemiluminescent Assay for Adamts-13 Activity. Clinical Performance and Cost-Effectiveness Analysis

Background: Thrombotic thrombocytopenic purpura (TTP) is a rare thrombotic microangiopathy (TMA) that can be caused by congenital or acquired severe deficiency of a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS-13), an enzyme that cleaves von Willebrand factor (VWF). ADAMTS-13 deficiency leads to the accumulation of ultra-large VWF multimers, leading to platelet aggregation and microthrombi formation. Aside clinical symptoms, the diagnosis of TTP is based on laboratory parameters such as thrombocytopenia, hemolytic anemia with the presence of schistocytes, and severely reduced activity of ADAMTS-13 (<10%). As TTP is a life-threatening condition characterized by microvascular thrombosis, it is of great importance to shorten the time to the treatment, and according to the French recommendations, patients with suspected TTP must be treated with the triplet therapy including plasma exchange (PEX), rituximab, and caplacizumab, plus corticosteroids until the results of ADAMTS-13 was obtained. As this therapy must be pursued only in the case of deficiency, a rapid ADAMTS-13 testing is critical for early diagnosis and optimal management of acute TTP. Design and aims of the study: We first retrospectively compared the performance of a rapid fully automated chemiluminescent assay (HemosIL AcuStar ADAMTS-13) to those of the FRETS-VWF73 assay in the diagnosis of TTP. Then, we compared the cost-effectiveness of a strategy based on the on-site measurement of ADAMTS-13 activity using the AcuStar assay vs. its centralized measurement in a reference laboratory, as it is currently the case at our institution. For that purpose, we created two scenarios based on either the local measurement of ADAMTS-13 activity with a maximum time-to-result of 16 hours (assay performed during daytime, 7/7) or its centralized measurement with a median time-to-result of 4 days (range: 2-8), as demonstrated from the 2018-2021 estimates. The triplet therapy was hypothesized to be started on admission and stopped if ADAMTS-13 activity was >10%. In case of ADAMTS-13 activity <10%, an inhibitor screening would be performed at the reference laboratory, as this assay was not expected to be locally implemented. For the calculation, we considered the costs of reagent, shipping/handling of the samples to the reference laboratory, laboratory staff workload, reimbursement rates, and treatments administered in patients with suspected TTP until availability of the ADAMTS-13 result. Results: In the plasma from 56 patients with acute TMA, ADAMTS-13 activity was not significantly different when evaluated using the HemosIL AcuStar ADAMTS-13 and the FRETS-VWF73 assays [median=72.6% (range: 0.2-126) vs. 79% (range: 5-150); p=0.08]. The concordance of test results as whether ADAMTS-13 activity was below (n=5) or above the threshold of 10% using the 2 assays was excellent (kappa=1.00), allowing an accurate diagnosis of the 5 patients with confirmed TTP. Based on the local activity between 2018 and 2021, there was a mean of 60 prescriptions of ADAMTS-13 activity per year. Most were for the follow-up of TTP patients and for patients with non-TTP TMA, whereas 7 were for the diagnosis of acute TTP, as suggested by the French score, which was confirmed in 4 cases (mean values). As shown in the Table, the local measurement of ADAMTS-13 activity was found to be cost-effective with a 16%-reduction of the costs compared to its centralized measurement in the 7 patients with suspected TTP during the first 4 days. This equates to 4,508 € saved per patient with suspected acute TTP. Conclusions: Together with its short turnaround time (33 min) and its full automation, our results suggest that the HemosIL AcuStar ADAMTS-13 activity assay could be an assay of choice to rapidly measure ADAMTS-13 activity in the plasma and thus to establish the diagnosis of acute TTP in emergency settings. Considering the local costs, using the strategy based on the local evaluation of ADAMTS-13 activity led to a 16%-reduction of the overall costs during the first 4 days after admission of the 7 patients with suspected acute TTP. Moreover, by dramatically decreasing the time-to-result (<1 day vs. 4 days), unnecessary potentially harmful and expensive treatments could be withheld earlier in patients in whom the diagnosis of TTP was ruled out based on an ADAMTS-13 activity >10%. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Differential Diagnosis Distinguishing Immune TTP from Septic DIC Using Plasma Levels of Haptoglobin and Factor XIII Activity

Introduction Differential diagnosis of immune thrombotic thrombocytopenic purpura (iTTP) and septic disseminated intravascular coagulation (DIC) in daily clinical practice is difficult. iTTP is diagnosed by deficiency of ADAMTS13 activity and ADAMTS13 inhibitor positivity. However, it is difficult to rapidly measure ADAMTS13 activity in real-time in clinical practice. Prompt therapeutic interventions are directly dependent on iTTP prognosis. A method for differentiating between these two disorders using common laboratory tests is needed. Plasma haptoglobin levels can indicate hemolysis and are reported to be severely decreased in iTTP. Coagulation factor XIII (FXIII) activity is also severely decreased in septic DIC. To date, no reports have observed haptoglobin in septic DIC or FXIII activity in iTTP. We analyzed the plasma levels of haptoglobin and FXIII activity in patients with iTTP and septic DIC to investigate whether these markers can be used for differential diagnosis. Methods iTTP was defined as <10% normal ADAMTS13 activity, and >0.5 BU/mL ADAMTS13 inhibitor. Septic DIC was defined as meeting both Third International Consensus Definitions for Sepsis and Septic Shock, and ISTH DIC diagnostic criteria. Thirty-five patients with iTTP and 30 with septic DIC were enrolled in this study. Plasma haptoglobin levels were measured using Human Quantikine ELISA Kits (#DPHAGO, R&D Systems, Inc., Minneapolis, USA), which is a highly sensitive method compared to methods used in clinical practice. Values are expressed as medians (first quartile-third quartile). Results As shown in the table, iTTP patients were significantly younger than those with septic DIC. The iTTP group showed significantly lower ADAMTS13 activity, higher ADAMTS13 inhibitor titer, lower hemoglobin level, lower platelet counts, higher LDH level, and lower creatinine level than the septic DIC group. In a comparison of coagulation and fibrinolytic markers, the septic DIC group had significantly higher PT-INR, prolonged APTT, higher FDP and D-dimer levels, and lower AT activity than the iTTP group. The plasma haptoglobin level was 0.39 mg/dL (0.18-0.76 mg/dL) in the iTTP group, and 54.2 mg/dL (0.6-143.9 mg/dL) in the septic DIC group (P < 0.01). FXIII activity was 91.3% (80.4-115.0%) in the iTTP group, and 36.3% (14.7-61.9%) in the septic DIC group (p<0.01). The ROC curve of haptoglobin and FXIII activity in the differential diagnosis of TTP and septic DIC were investigated. The cut-off level of haptoglobin was 2.868 mg/dL, the area under the curve (AUC) was 0.832 (95% CI:0.727-0.938), specificity was 66.7%, and sensitivity was 100%. The cutoff level of FXIII activity was 76.0%, AUC was 0.931 (95%CI:0.873-0.989), specificity was 77.1%, and sensitivity was 93.3%. We developed a scoring system to differentiate iTTP from septic DIC using a combination of FXIII activity and haptoglobin; TTP/DIC index = plasma FXIII activity (%) - plasma haptoglobin (mg/dL). Laboratory TTP was defined when the index was ≥60, and laboratory DIC was defined when the index was <60. The AUC for the combination of FXIII activity and haptoglobin was 0.968 (95% CI: 0.9354-1). The accuracy of iTTP diagnosis in laboratory TTP was 89.2% (33/37), and the accuracy of septic DIC diagnosis in laboratory DIC was 92.9% (26/28). Conclusions A comparison of iTTP and septic DIC showed significant differences in haptoglobin and FXIII activity levels. A combination of haptoglobin and FXIII activity was considered helpful in differentiating iTTP from septic DIC. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Validation of PLASMIC score in a cohort of patients with suspected thrombotic microangiopathy in an academic medical centre.

The PLASMIC score is a rapid and inexpensive clinical assessment tool for predicting severe ADAMTS13 deficiency (<10% activity) in patients with suspected thrombotic thrombocytopenic purpura (TTP). The score includes 7 parameters: absence of active cancer, patient not having received stem cell transplant or organ transplant, platelet count <30×109/L, haemolysis, mean corpuscular volume <90 fl, International Normalized Ratio <1.5, and serum creatinine <2 mg/dL. In this retrospective study, we evaluated a cohort of 59 consecutive patients with suspected thrombotic microangiopathy who had been referred to the Hemostasis and Thrombosis Center of the "Federico II" University of Naples, Italy, for measurement of ADAMTS13 activity. Relevant clinical and laboratory information were collected for all patients. The PLASMIC score was calculated in 52 of the 59 patients included in the study. In the high-risk group (PLASMIC score 6 or 7), 12 out of 20 patients (60%) had ADAMTS13 <10%. Interestingly, all 6 patients (100%) with PLASMIC score 7 had ADAMTS13 <5%. In the intermediate risk group (score 5), only one case out of 17 (5.9%) had ADAMTS 13 <10%. In the low-risk group (score 0-4), none of the patients had severe ADAMTS13 deficiency. The collected data enabled the sensitivity and specificity of PLASMIC score in TTP to be calculated, achieving 92% (95% CI: 0.80-0.98) and 79% (95% CI: 0.66-0.89), respectively. The PLASMIC score was seen to be a very efficient tool in distinguishing between patients with severe ADAMTS13 deficiency from those without, with an AUC of 0.92 (95% CI: 0.82-1.0; p<0.001). In our cohort, a high-risk PLASMIC score successfully predicted patients with severe ADAMTS13 deficiency, allowing the clinician to quickly define the best therapeutic approach, especially useful for those clinicians not used to the diagnosis and treatment of thrombotic microangiopathies.

Incidence of thrombotic microangiopathies in Quebec: insight from a laboratory centralizing ADAMTS-13 testing

BackgroundThrombotic microangiopathies (TMA) are serious medical conditions requiring a prompt diagnosis to adapt treatment. The determination of ADAMTS-13 activity enables discriminating thrombotic thrombocytopenic purpura (TTP) from other forms of TMA. The purpose of this study was to provide an estimate of the incidence of TTP and TMA in the Canadian Quebec province using data collected from a laboratory centralizing ADAMTS-13 testing for the whole province.ResultsFrom 2012 to 2019, 846 patients were evaluated for plasma ADAMTS-13 activity due to a suspicion of TMA. TTP was identified in 147 patients. Of these, 118 patients with a median age of 51.5 years and a male–female ratio of 1:1.4 had their first episode of TTP during the study period. The number of ADAMTS-13 tests performed and the number of patients with suspected TMA increased annually by 19% and 21% respectively. While the incidence of non-TTP TMA increased annually, that for TTP remained unchanged. This averaged 10.2 (95% CI 5.9–14.4) per million persons per year for suspected non-TTP TMA and 1.8 (95% CI 1.3–2.4) for confirmed TTP. The incidence rate of TMA other than TTP was higher in the age group 70–79 years (21.8; 95% CI 5.4–38.1) for females and in the age group 80–89 years (24.4; 95% CI 7.2–41.7) for males compared to other age groups. The incidence rate of TTP was higher in the age group 40–49 years (4.0; 95% CI 2.0–5.9) for women and in the age group 60–69 years (3.4; 95% CI 1.1–5.6) for men compared to other age groups.ConclusionThe analysis of centralized data measuring ADAMTS-13 activity allowed us to adequately establish the incidence rate and demographic characteristics of TMA, particularly TTP, in Quebec. TTP incidence remained stable while suspected non-TTP TMA steadily increased from 2012 to 2019.

Long-Term Renal Outcomes in Hereditary TTP Patients: Data from the International Hereditary TTP Registry

IntroductionHereditary thrombotic thrombocytopenic purpura (hTTP) is an ultra-rare thrombotic microangiopathy caused by autosomal recessively inherited severe ADAMTS13 deficiency. In respect to organ damage, we recently reported a heterogeneous clinical course with some patients having various degrees of organ damage while others are almost asymptomatic*. The long-term consequences of hTTP are still not fully known.MethodsWe analyzed the prevalence and development of renal disease in confirmed hTTP patients in the International Hereditary TTP Registry until July 2021. We studied the onset of kidney disease, the presence of additional co-morbidities and the possibility of a specific genotype-phenotype correlation. We classified different renal diseases of our hTTP patients, according to the ICD-10 code (version 2016) as described in Table 1.ResultsThirty-five (21%) of 163 confirmed hTTP patients of the International TTP Registry with a mean age at enrolment of 38.2 years had kidney disease. 80% were Caucasian, 8.5% Asian and 11.5% indicated other ethnicities.According to the ICD-10 code classification, two patients had acute kidney disease (AKI, ICD code N17) not specified during acute TTP episodes. Among 18 patients with general CKD, we could identified three patients with chronic kidney disease (CKD, ICD code N18) stages 1-2; four with CKD stage 3, and four patient with CKD stage 5. In two patients, kidney disease was unspecified (ICD code N19). Five patients had diagnoses of certain specific renal diseases, such as acute glomerulonephritis (ICD code N00), unspecified nephritis syndrome (ICD code N05), recurrent and persistent hematuria (ICD code N02), and calculus of the kidney (ICD code N20) (Table 1). Seven patients developed end-stage renal disease requiring renal replacement therapy (ICD code Z99.2), which was temporarily needed in four additional patients (Z49.2). Two patients underwent kidney transplantation (ICD code Z94) (Table 1).The 163 hTTP patients experienced 625 acute disease episodes, of which 108 (17%) were associated with acute renal failure. 21/163 (13%) acute episodes were treated with hemodialysis. After experiencing several hTTP episodes with acute renal failure, 15 patients developed CKD at different stages.26/35 (74%) hTTP patients with kidney disease presented also other co-morbidities: hypertension in 14 patients, 10 and 18 patients had suffered from transient ischemic attacks and/or strokes, and six patients had suffered from a myocardial infarction. We observed no apparent correlation between onset of CKD and presence of co-morbidities.Regular plasma prophylaxis was introduced in 26/35 hTTP patients with kidney disease; in the majority of them (64%) plasma treatment was started due to CKD or after CKD diagnosis.Of the 35 patients with renal disease, 15 were homozygous and 20 compound heterozygous ADAMTS13 mutation carriers. The most known ADAMTS13 mutation c.4143_4144dupA counts 33% of the whole hTTP patients in our database (54/163 patients). It was the most represented mutations in our cohort of hTTP patients with renal disease (60%, 21/35): 11 homozygous and 10 compound heterozygous carriers. Nevertheless, we did not observe a specific genotype-phenotype correlation.ConclusionsOur analysis of the International Hereditary TTP Registry cohort (at present 163 patients) showed that the majority of patients had a diagnosis of hTTP before a diagnosis of kidney disease, especially CKD. We could not identify a correlation with the onset of additional co-morbidities or with the genotype; nevertheless we cannot exclude that it may be present. Considering that 43% (15/35) patients developed CKD after several acute episodes with acute renal failure, a closer and attentive care for those patients not yet developing CKD to avoid or delay the onset is highly recommended. Hence, to evaluate the contribution of acute hTTP episodes and of other co-morbidities to the development of kidney disease requires further in depth analyses. More frequent and long-term follow-up visits are needed to better understand the long-term outcome and development of kidney disease in hTTP patients.* Tarasco et al, Blood 2021 [Display omitted] DisclosuresMatsumoto: Sanofi: Consultancy; Takeda: Consultancy; Alexion Pharma: Consultancy; Asahi Kasei Pharma: Research Funding; Chugai Pharmaceutical: Research Funding; Alfesa Pharma: Patents & Royalties: ELISA for measuring ADAMTS13 activity. Lämmle: Takeda: Membership on an entity's Board of Directors or advisory committees; Ablynx: Membership on an entity's Board of Directors or advisory committees, Other: Travel Support, Speakers Bureau; Baxter: Other: Travel Support, Speakers Bureau; Alexion: Other: Travel Support, Speakers Bureau; Siemens: Other: Travel Support, Speakers Bureau; Bayer: Other: Travel Support, Speakers Bureau; Roche: Other: Travel Support, Speakers Bureau; Sanofi: Other: Travel Support, Speakers Bureau. Kremer Hovinga Strebel: Baxalta US Inc: Other: grant; Shire: Consultancy, Speakers Bureau; Ablynx: Consultancy, Speakers Bureau; Federal Office of Public Health: Consultancy; Insel Gruppe AG: Current Employment.

The Efficacy and Safety of Caplacizumab in Japanese Patients with Immune-Mediated Thrombotic Thrombocytopenic Purpura (iTTP): An Open-Label, Phase 2/3 Study

The Efficacy and Safety of Caplacizumab in Japanese Patients with Immune-Mediated Thrombotic Thrombocytopenic Purpura (iTTP): An Open-Label, Phase 2/3 Study

Low ADAMTS13 Activity Correlates with Increased Mortality in COVID-19 Patients

Systemic inflammation and coagulopathy are characteristic hallmarks of COVID19. “COVID coagulopathy” manifests mainly as a prothrombotic state affecting both large and small blood vessels, and presenting as arterial, venous, and microangiopathic thrombotic events with von Willebrand factor (VWF) and soluble thrombomodulin increased in hospitalized patients. The causes of coagulopathy are poorly understood. Aim: To investigate the relationship between von Willebrand factor (VWF) biomarkers, intravascular hemolysis, coagulation, and organ damage in COVID19 patients and to study their association with disease severity and mortality. Methods: 181 hospitalized adult COVID19 patients were randomly selected with a balanced distribution of survivors and non-survivors during the period of March 26th 2020 to May 5th 2020. The medical records and laboratory values were reviewed. Statistical analysis was performed using R studio V.3.6.2. Results: Patients who died (n=90) had significantly lower ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity, elevated lactate dehydrogenase levels, increased schistocyte/RBC fragment counts, and elevated VWF antigen and activity levels compared to patients discharged alive (n=91). In 31 patients, we measured several of these biomarkers on two or more occasions. The trending of ADAMTS13 activity illustrated that it is not steady throughout the hospitalization course. ADAMTS13 activity levels tended to improve and/or reach normal levels in patients that survived, yet ADAMTS13 activity levels worsened in most patients that died. Likewise, the VWF antigen and activity levels tended to decrease in patients that survived whereas tended to increase well above the normal range (2-3 folds) in patients that died. D-Dimer levels trended downwards in survivors, sometimes to levels less than 1 µg/ml, yet tended to increase in patients who died. Given the relationship between ADAMTS13 activity and mortality, we wanted to determine a cut-point of initial ADAMTS13 activity (within 72 hours from admission) to predict mortality. 102 patients in our cohort had an ADAMTS13 activity measurement within this timeframe. We determined that this optimal cut-point of initial ADAMTS13 activity was 43% using Youden’s J statistic. Only 30% of patients who had an ADAMTS13 activity level of less than 43% on admission survived, yet 60% of patients survived who had an ADAMTS13 activity level of greater than 43% on admission. Conclusions: COVID-19 may present with low ADAMTS13 activity in a subset of hospitalized patients. Presence of schistocytes/RBC fragment and elevated D-dimer levels on admission may warrant a work-up for ADAMTS13 activity and VWF antigen and activity levels. These findings indicate the need for future investigation to study the relationship between endothelial and coagulation activation and the efficacy of treatments aimed at prevention and/or amelioration of microangiopathy in COVID-19.

Recognizing and managing hereditary and acquired thrombotic thrombocytopenic purpura in infants and children.

We describe how infants and children with hereditary and acquired autoimmune thrombotic thrombocytopenic purpura (TTP) initially present and how they can be promptly diagnosed and effectively managed. These are uncommon disorders that are commonly misdiagnosed and can be rapidly fatal. TTP is caused by a severe deficiency of the plasma protease, A disintegrin and Metalloprotease with a ThromboSpondin type 1 motif, member 13 (ADAMTS13). Measurement of ADAMTS13 activity is becoming easily accessible. A common presentation of hereditary TTP is neonatal severe hemolysis and hyperbilirubinemia. However, the median age of diagnosis is not until 5.5years. Plasma is effective treatment for exacerbations and for prophylaxis. Plasma may be replaced by recombinant ADAMTS13 when it becomes available. Acquired TTP is more frequent in older children, in whom it is more common in girls and is commonly associated with systemic lupus erythematosus. For acquired TTP, plasma exchange and immunosuppression are the current treatment for acute episodes; caplacizumab is now commonly used in adults and may replace plasma exchange.

Comparative Analysis of Clinical Prediction Scores in Acquired Thrombotic Thrombocytopenic Purpura: The Superiority of Plasmic Score

Background: Acquired thrombotic thrombocytopenic purpura (aTTP) is a rare and life-threatening hematologic disorder. The decision to start plasma exchange is challenging in clinical practice, due to aTTP rarity, and the extensive differential diagnosis with other thrombotic microangiopathies (TMA). Although the ADAMTS13 activity measurement is essential to aTTP diagnosis, a rapid quantification is unavailable in most centers, being necessary to develop clinical prediction models to evaluate severe enzymatic deficiency. The first model developed was Bentley score, followed by French score and more recently PLASMIC score. Studies comparing these 3 methods are scarce. The criteria of published scoring models are summarized in Table1 Aim: To compare and evaluate the discriminative power of the Bentley, French and PLASMIC scores in predicting severe ADAMTS13 deficiency (≤10%) in our group of patients (pts). Methods: We performed a retrospective analysis of pts with ADAMTS13 activity tested between 2008 and 2019, in a single center. Pts were divided in two groups: ADAMTS13 activity ≤10% (ADAMTS13≤10%) and &amp;gt;10% (ADAMTS13&amp;gt;10%) and then stratified according to the 3 scores. We evaluate sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) to predict low ADAMTS13 activity. Diagnostic accuracy was tested using the area under the ROC curve. A P-value of &amp;lt;0.05 was considered statistically significant. Results: ADAMTS13 activity was evaluated in 119 pts with suspected aTTP. There was a female predominance (60.5%; n=72) and the mean age was 54±20 years. Thirty-one pts had ADAMTS13≤10% and 27 (87.1%) of them had been diagnosed with aTTP, two were inherited thrombotic thrombocytopenic purpura and the other two were sepsis associated TMA. Comparing the groups ADAMTS13≤10% and ADAMTS13&amp;gt;10%, pts in the first were younger (46±18 vs 57±21 years; p=0.008), had lower platelet count (23.04±27.1 vs 47.79±37.6x109/L; p&amp;lt;0.001), and lower creatinine value (1.25±0.8 vs 2.92±4.2 mg/dL; p&amp;lt;0.017). ADAMTS13≤10% group had a higher reticulocyte count (5.99±5.0 vs 3.46±3.4%; p=0.005) and higher indirect bilirubin levels (2.59±2.1 vs 1.59±2.2 mg/dL; p=0.013). There were no statistical differences in hemoglobin, MCV, INR, D-Dimers and antinuclear antibodies (ANA's) positivity among the two groups. PLASMIC score was calculated in all pts. Due to missing data, Bentley score was only applied in 44.5% (n=53) and French score in 54.6% (n= 65) pts. Using a high-risk PLASMIC score as the predictor, the sensitivity was 80.6%, specificity 78.4%, PPV 56.8% and NPV 92.0%. The C-statistics for high PLASMIC score cut-offs (&amp;gt;5 points) was 0.80 (95% confidence interval [CI] 0.70-0.89) (fig.1). Applying high-risk Bentley score vs low-to-intermediate-risk score, the sensitivity was 44.4%, specificity 94.3%, PPV 80.0% and NPV 76.7%. The C-statistics was 0.69 (95% CI 0.53-0.86) using the high Bentley score cut-offs (fig.2). The French score had higher sensitivity (83.3%), but lower specificity (36.2%), with 33.3% of PPV and 85.0% of NPV. Using the high French score cut-offs, the C-statistics was 0.60 (95% CI 0.45-0.75) (fig.3). There were not statistically significant differences between PLASMIC and Bentley scores in the ability to predict low ADAMTS13 activity, and both performed better than French score (p&amp;lt;0.001; p=0.02, respectively). Conclusion: In our cohort, the PLASMIC score showed to be the most balanced and efficient clinical prediction score, with high sensitivity and specificity. Bentley score was also a good predictor of ADAMTS13 activity, but had lower sensitivity and less applicability; French score was comparatively inferior. Pts with low PLASMIC score are highly unlikely to have ADAMTS13 deficiency. PLASMIC score is easy to calculate and readily usable in most emergency settings while the French and Bentley scores require additional laboratory data, which is not always accessible. These results support the previously published data, showing PLASMIC score as a helpful complementary tool in clinical practice recognizing high-risk pts when ADAMTS13 activity measurement is not available. Disclosures No relevant conflicts of interest to declare.

The ADAMTS13-VWF axis is dysregulated in chronic thromboembolic pulmonary hypertension.

Chronic thromboembolic pulmonary hypertension (CTEPH) is an important consequence of pulmonary embolism that is associated with abnormalities in haemostasis. We investigated the ADAMTS13–von Willebrand factor (VWF) axis in CTEPH, including its relationship with disease severity, inflammation, ABO groups and ADAMTS13 genetic variants.ADAMTS13 and VWF plasma antigen levels were measured in patients with CTEPH (n=208), chronic thromboembolic disease without pulmonary hypertension (CTED) (n=35), resolved pulmonary embolism (n=28), idiopathic pulmonary arterial hypertension (n=30) and healthy controls (n=68). CTEPH genetic ABO associations and protein quantitative trait loci were investigated. ADAMTS13–VWF axis abnormalities were assessed in CTEPH and healthy control subsets by measuring ADAMTS13 activity, D-dimers and VWF multimeric size.Patients with CTEPH had decreased ADAMTS13 (adjusted β −23.4%, 95% CI −30.9– −15.1%, p<0.001) and increased VWF levels (β +75.5%, 95% CI 44.8–113%, p<0.001) compared to healthy controls. ADAMTS13 levels remained low after reversal of pulmonary hypertension by pulmonary endarterectomy surgery and were equally reduced in CTED. We identified a genetic variant near the ADAMTS13 gene associated with ADAMTS13 protein that accounted for ∼8% of the variation in levels.The ADAMTS13–VWF axis is dysregulated in CTEPH. This is unrelated to pulmonary hypertension, disease severity or markers of systemic inflammation and implicates the ADAMTS13–VWF axis in CTEPH pathobiology.

Thrombotic thrombocytopenic purpura: diagnostic criteria, clinical features, and long-term outcomes from 1995 through 2015.

Our objective was to describe new observations from the Oklahoma Thrombotic Thrombocytopenic Purpura (TTP) Registry experience (November 1995 through December 2015) on the diagnosis of TTP along with patients' clinical features and their outcomes. Among 363 patients with an initial episode of clinically suspected TTP, the diagnosis of TTP was supported by both ADAMTS13 activity <10% and clinical features in 78 patients (21%). ADAMTS13 activity was measured in all 363 patients by 2 methods: fluorescence resonance energy transfer (FRET) and immunoblotting (IB). Sixty patients had ADAMTS13 activity <10% by both methods, 15 had ADAMTS13 <10% only by FRET, and 3 had ADAMTS13 <10% only by IB. Five patients with ADAMTS13 activity <10% by 1 method had an alternative clinical diagnosis, not TTP. Two patients with characteristic clinical features of TTP (microangiopathic hemolytic anemia and thrombocytopenia, no alternative diagnosis) and multiple relapses initially had ADAMTS13 activity >10% by both measurements. ADAMTS13 inhibitor titers were not associated with presenting features or outcomes. Microangiopathic hemolytic anemia and thrombocytopenia were not severe in all patients. Forty-seven percent of patients had no or minor neurologic abnormalities; 95% had no or minor serum creatinine abnormalities. Ten patients (13%) died, 2 before completing 1 plasma exchange (PEX); 3 deaths were attributed to PEX complications. For patients presenting after we began using rituximab in some patients (December 2003), fewer PEX treatments were required and fewer relapses occurred. Patients with their first relapse presented with higher platelet counts and hematocrits and lower lactate dehydrogenase levels and required fewer PEX treatments compared with their initial episodes.

Quinine-Induced Thrombotic Microangiopathy (Q-TMA): Frequency, Presenting Features, Outcomes

Q-TMA is an acute, severe, immune-mediated, drug-induced disorder. Q-TMA is suspected when symptoms suddenly begin within hours following quinine (Q) exposure. Diagnosis of Q-TMA is established by the history of recurrent acute symptoms following recurrent Q exposures and/or by documentation of Q-dependent antibodies reactive with platelets and/or neutrophils. The Oklahoma TTP-HUS Registry enrolls all patients for whom plasma exchange (PEX) is requested for suspected TTP or HUS. Since 1995, when routine measurement of ADAMTS13 activity began, the Registry has diagnosed 78 patients with acquired TTP (ADAMTS13 <10%). During this time we have also diagnosed 17 patients with Q-TMA; 2 additional patients were diagnosed before 1995. Seventeen of these 19 patients were tested for Q-dependent antibodies; all were positive. Nine patients had a history of recurrent acute symptoms with recurrent Q exposure, including the 2 patients not tested for Q-dependent antibodies. Q exposure was a pill in 18 patients, tonic water in one. Remarkably, 18 patients were women; all 19 patients were white. Common presenting symptoms were fever, chills, nausea and vomiting. No patients had focal neurologic abnormalities. All patients had microangiopathic hemolytic anemia (MAHA), thrombocytopenia, and acute kidney injury. Eight patients had elevated serum alanine aminotransferase (231-1345 U/L). Three patients had neutropenia (absolute neutrophil counts, 184-486). Two patients had coagulation abnormalities suggesting disseminated coagulation (DIC).One patient died from complications of the central venous catheter insertion, performed for PEX and dialysis; all other patients recovered normal platelet counts. Three of the 18 surviving patients had end-stage renal disease (2 had kidney transplants). The median estimated glomerular filtration rate (GFR) for the other 15 patients, at 2.7-19.2 years (median, 10.2) after recovery, was 36 ml/min (range, 19-98). Only two patients had normal GFR (≥90 ml/min). Eleven patients had chronic kidney disease, defined by GFR <60 ml/min. Seven of 18 patients have died 4.1-12.7 years (median, 7.8) following recovery at ages 59-87 years. Conclusion. Quinine can cause severe immune-mediated toxicities involving multiple organ systems (Am J Hematol 2016; 91: 461). Q-TMA is an acute disorder causing severe kidney injury and, in some patients, also liver toxicity, neutropenia, and/or DIC. Q-TMA is not rare. During 20 years, we enrolled 17 Q-TMA patients compared to 78 patients with acquired TTP. Chronic kidney disease is a common long-term outcome. Explicit questions are required to discover the association of systemic symptoms with quinine ingestion. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.