Diagnosis and follow-up of thrombotic thrombocytopenic purpura with an automated chemiluminescent ADAMTS13 activity immunoassay.

BACKGROUND: Thrombotic thrombocytopenic purpura (TTP) is a life-threatening thrombotic microangiopathy (TMA) caused by a severe functional deficiency in ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type I repeats-13), the specific von Willebrand factor (VWF) cleaving protease. ADAMTS13 activity is essential to diagnose TTP but remains challenging to assess, as reference ADAMTS13 activity assays are manual and time consuming. Current techniques also lack robustness in low detectable ADAMTS13 activity range, which could prove problematic for therapy-driven monitoring. OBJECTIVES: The HemosIL AcuStar ADAMTS13 activity assay is a fast, automated chemiluminescent assay, the performance of which remains to be evaluated prospectively on very large cohorts of patients with TMA and in real-life conditions. PATIENTS AND METHODS: Our study was conducted over two successive sequences: a retrospective evaluation followed by a "real-life" prospective evaluation. Overall, we evaluated the HemosIL AcuStar ADAMTS13 activity assay on 539 citrated plasma samples. We extensively studied linearity, limit of detection, contamination, intra-assay and interassay precisions with a specific focus on levels < 25 IU/dL. Diagnostic performances for the detection of < 10 IU/dL ADAMTS13 activity and overall method comparison were conducted with the fluorescence resonance energy transfer (FRETS)-VWF73 assay as the reference method. RESULTS: Technical performance proved excellent. Robustness in low detectable ADAMTS13 activity range was good, potentially qualifying this assay for therapy-driven monitoring. Comparison with the FRETS-VWF73 assay was satisfactory (r 2 = .83, P < .0001) as were the diagnostic performances for acute-phase TTP (specificity, 99.7%; positive predictive value, 99.2%). CONCLUSION: The HemosIL AcuStar ADAMTS13 activity assay is a fast, reliable, automated technique well adapted as a first-line ADAMTS13 activity assay for TTP diagnosis and follow-up.

ADAMTS13 and von Willebrand factor assessment in steady state and acute vaso-occlusive crisis of sickle cell disease.

BACKGROUND: Sickle cell disease (SCD) is characterized by vaso-occlusive crisis (VOC), acute chest syndrome (ACS) and multiorgan failure (MOF) complicated by thrombosis. Von Willebrand factor (VWF) is a strong marker of SCD-related endothelial injury. OBJECTIVES: To decipher the role of VWF and its specific-cleaving metalloprotease, ADAMTS13, in the vaso-occlusive and thrombotic process of SCD. PATIENTS/METHODS: We investigated the VWF antigen (Ag), ADAMTS13 activity, ADAMTS13 Ag and ADAMTS13 IgGs in a cohort of 65 patients with SCD prospectively enrolled in a 20-month period from three centers. Patients were divided into two groups: an asymptomatic group (n = 30) with treated or untreated SCD at steady state, and a VOC/ACS group (n = 35) with SCD with VOC/ACS requiring either medical management or intensive care management for MOF. RESULTS AND CONCLUSIONS: VWF:Ag levels were increased (median, 167 IU/dL; interquartile range [IQR], 124 - 279), especially in patients with VOC SCD (227 IU/dL; IQR, 134-305; P = .04), and positively correlated with inflammatory markers (P < .02). Median ADAMTS13 activity was normal (70 IU/dL; IQR, 60-80), but 7 patients exhibited a partial deficiency between 25 and 45 IU/dL. ADAMTS13 activity/VWF:Ag ratio, however, did not change during VOC. Median ADAMTS13:Ag was slightly decreased (611 ng/mL; IQR, 504-703) with no significant difference between groups. Surprisingly, ADAMTS13 IgGs were detected in 33 (51%) of our patients. We conclude that, in SCD, VWF:Ag and nonrelevant ADAMTS13 IgGs may reflect the severity of the inflammatory vasculopathy enhancing vaso-occlusive and thrombotic complications.

Loss of von Willebrand factor high-molecular-weight multimers at acute phase is associated with detectable anti-ADAMTS13 IgG and neurological symptoms in acquired thrombotic thrombocytopenic purpura.

INTRODUCTION: Thrombotic thrombocytopenic purpura (TTP) is a rare life threatening thrombotic microangiopathy caused by a severe functional deficiency of ADAMTS13, most frequently due to autoantibodies to ADAMTS13, thus termed acquired autoimmune TTP. ADAMTS13 specifically regulates the adhesive activity of von Willebrand factor (VWF) by cleaving its high-molecular-weight multimers (HMWM). We investigated whether VWF-HMWM level at acute phase of TTP could be a predictive factor for morbidity. MATERIAL AND METHODS: We gathered clinical and biological data from a cohort of 114 patients with acquired TTP at acute phase. VWF-HMWM were assessed by electrophoretic analysis and by an ELISA measuring the capacity of VWF to bind to collagen (VWF:CB), and linear correlation between these two methods was carried out. We cross-referenced clinical and biological data with VWF-HMWM levels. RESULTS: VWF-HMWM levels were heterogeneous, but half of our patients were below normal range (50% if assessed by electrophoresis; 47.4% if assessed by ELISA). The correlation study between electrophoresis and ELISA reached statistical significance (r2 = 0.5979; p < 0.0001). Statistical analysis showed that loss of VWF-HMWM as assessed by VWF:CB < 70 IU/dL is associated with detectable anti-ADAMTS13 antibodies, severe neurological symptoms and thrombocytopenia (p < 0.05). CONCLUSION: Our results confirm that VWF-HMWM can be satisfactorily assessed by VWF:CB, much easier to perform than electrophoresis. The association highlighted between loss of VWF-HMWM, detectable anti-ADAMTS13 IgG and neurological symptoms may offer new insights to understanding the pathophysiology of acquired auto-immune TTP.

Evaluation of a chromogenic commercial assay using VWF-73 peptide for ADAMTS13 activity measurement.

INTRODUCTION: Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy (TMA), related to a severe functional deficiency of ADAMTS13 activity (<10% of normal). ADAMTS13 activity is thus crucial to confirm the clinical suspicion of TTP, to distinguish it from other TMAs, and to perform the follow-up of TTP patients. MATERIAL AND METHODS: We compared the performance of the commercial chromogenic assay Technozym ADAMTS13 Activity ELISA (chromogenic VWF73 substrate, Chr-VWF73, Technoclone, Vienna, Austria), to that of our in-house FRETS-VWF73 used as reference method. A large group of 247 subjects (30 healthy volunteers and 217 patients with miscellaneaous TMAs) was studied. RESULTS: The lower limit of detection of the Chr-VWF73 was 3%, which is well adapted to the clinically relevant threshold for TTP diagnosis (10%). Our results showed a reasonable agreement between FRETS-VWF73 and Chr-VWF73 assays to distinguish samples with an ADAMTS13 activity <10% from those with an ADAMTS13 activity >10%. However, Chr-VWF73 assay provided false negative results in ~12% of acute TTP patients. Inversely, the Chr-VWF73 assay globally underestimated ADAMTS13 activity in detectable values ranging from 11 to 100% (with a great variability compared to FRETS-VWF73), which may be a concern for the follow-up of TTP patients in remission. CONCLUSION: In-house assays developed and performed by expert laboratories remain the reference methods that should be used without limitation to control values provided by commercial assays when needed. Also, the development of an international reference preparation will be crucial to improve standardization.