Measurement of von Willebrand factor-cleaving protease (VWF-CP) activity is useful for diagnosis of thrombotic thrombocytopenic purpura (TTP), but the current methods are cumbersome. We recently introduced a simple method of TTP detection using the Cone and Plate(let) Analyzer (CPA), that was based on the observation that mixing of acute TTP plasma (50 μL) with normal whole blood (150 μL) induces a significant increase in platelet deposition (surface coverage, %SC) on polystyrene surface under flow condition (1800 s−1) (

Brit J Haematol, 120: 597, 2003
). The test was specific for TTP, since plasma from patients with HUS, APLS, ITP or HIT did not affect normal platelet deposition. In this study, we further explored the potential use of the CPA method in differential diagnosis of inherited and acquired TTP by increasing the shear rate and by inducing the VWF-CP activity with BaCl2. TTP or normal plasma was mixed with normal blood (type O+) and the surface covered by platelets was tested under shear rates ranging between 1800 s−1 to 2500 s−1. Maximal difference in SC between TTP and normal plasma was observed at a shear rate of 2050 s−1. Under these conditions, plasmas of 5 patients with inherited TTP (ITTP), and 11 patients with acquired TTP (ATTP) yielded comparable increase in SC of normal platelets in whole blood, i.e. 77±19% and 78±17%, respectively. However, experiments in which BaCl2 was added to allow activation of VWF-CP resulted in a substantial distinction between inherited and acquired TTP plasma. While addition of BaCl2 to normal or inherited TTP plasma, both mixed with normal blood, yielded similar reductions of SC by 41±12% and 51±19%, only 11±4% reduction of SC was observed when acquired TTP plasma was used. These results suggest that when normal or inherited TTP plasma is mixed with normal blood, activation of VWF-CP cleaves large VWF multimers giving rise to substantial reduction in SC, whereas in the case of acquired TTP plasma the inhibitor of VWF-CP abolishes BaCl2-induced activation of VWF-CP and the ensuing reduction in SC. We conclude that introduction of BaCl2 in the CPA at high shear conditions may be useful for differentiation between inherited and acquired TTP.

Topics:
retinal cone, thrombotic thrombocytopenic purpura, adamts13 protein, hemolytic-uremic syndrome, inosine triphosphate, purpura, thrombocytopenic, idiopathic, polystyrenes, blood platelets, whole blood

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2005, The American Society of Hematology
2004
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