|
|
Background: The biological variability of von Willebrand factor and the variability in assays can make diagnosis and subclassification of von Willebrand disease (VWD) difficult. We describe a case series of four patients with a typical history of VWD and prolonged closure time in the platelet function analyser (PFA-100) but initially a nor-mal ratio of ristocetin cofactor activity (VWF:RCo) to von Willebrand factor antigen levels (VWF:Ag) for whom further diagnostics verified VWD type 2A.
Methods: For the initial VWD diagnostics we measured VWF:Ag, VWF:RCo, platelet aggregation induced by ADP, ristocetin and collagen, closure time in the PFA-100 test, and platelet count. We used VWF multimer analy-sis and collagen binding capacity for extended diagnostics. VWD diagnostics were carried out as part of extensive laboratory screening to exclude other haemostatic defects.
Results: Multimer analysis revealed the absence of ultralarge multimers in all 4 patients. Ristocetin-induced plate-let aggregation was consistently diminished in three patients with hereditary VWD 2A but not in a patient with es-sential thrombocythaemia. After repeat testing, diminished VWF:RCo and collagen binding capacity (VWF:CB) could be identified in all patients. However, all four cases would have been missed if the initial VWD assays had been performed only once.
Conclusions: A single measurement of a normal ratio of VWF:RCo/VWF:Ag does not exclude VWD 2A in pa-tients with a typical history of VWD. The PFA-100 is suitable for screening. To ensure that no cases of VWD are missed, multimer analysis and repeat functional testing of platelet aggregation, VWF:RCo, and VWF:CB are nec-essary.
DOI: 10.7754/Clin.Lab.2012.120112
|
