Background: The absence of large von Willebrand factor (VWF) multimers in patients with thrombotic thrombocytopenic purpura (TTP) had been demonstrated in several studies, which can probably be explained by a sequestration of these large multimers within the microthrombi. This characteristic can be measured by electrophoresis of VWF multimers or some testing methods reflecting VWF activity, and thus might be useful for diagnosis and prognosis of TTP. However, many of these methods are time-consuming.

Aims: To evaluate the diagnostic value of the VWF activity / VWF antigen ratio for TTP at acute phase.

Methods: In a consecutive cohort of 71 patients with suspected TTP and admitting our hospital in 2019, we analysed the levels of VWF activity and VWF antigen at acute phase, the diagnosis of TTP was defined as ADAMTS13 activity < 10%. The VWF activity was measured by an automatic immunoturbidimetric assay, based on a specific anti-VWF monoclonal antibody directed against the platelet binding site of VWF (Glycoprotein Ibreceptor).

Results: All of these included patients manifested remarkable thrombocytopenia (< 50×10⁹ platelets/L) and microangiopathic hemolytic anemia. Eventually, these patients were diagnosed as TTP (n=22), hemolytic uremic syndrome (n=9), disseminated intravascular coagulation (n=18), megaloblastic anemia (n=3), myelodysplastic syndrome (n=1), and thrombotic microangiopathies secondary tocollagen disease (n=8), malignancy (n=7), organ transplantation (n=2) and HELLP syndrome (n=1).The ratio of VWF activity to VWF antigen was significantly lower in patients with TTP than in those without (P< 0.001), the median (interquartile range) were 0.69 (0.63-0.73) and 0.91 (0.78-1.04), respectively. The ratio of VWF activity to VWF antigen < 0.75 could yield a sensitivity of 90.9% and a specificity of 77.3% for TTP diagnosis.

Conclusions: The ratio of VWF activity to VWF antigen based on automatic immunologic assays might be useful for differential diagnosis of TTPat acute phase, especially when the ADAMTS13 assay is not available in time.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/differential-diagnosis-of-thrombotic-thrombocytopenic-purpura-at-acute-phase-by-the-ratio-of-vwf-activity-to-vwf-antigen-based-on-automatic-immunologic-assays/