Potential laboratory misdiagnosis of hemophilia and von Willebrand disorder owing to cold activation of blood samples for testing

To assess the potential for misdiagnosis of von Willebrand disorder (nuWD) and hemophilia A while following current National Committee for Clinical Laboratory Standards (NCCLS) guidelines and consequent to a poorly recognized cold-activation phenomenon, we processed 39 normal citrate-anticoagulated samples by standard procedures (reference) or stored at low (similar to4degreesC) or ambient (similar to22degreesC) temperature for 3.5 hours before centrifugation and processing. Samples were tested in parallel for several hemostasis factors, including von Willebrand factor (nuWF). Similar results were obtained for all samples for factors II, V, VII, IX, X, XI, and XII. For factor VIII (FVIII) and nuWF, only samples stored at ambient temperature had results comparable to reference sample results. In most cases, low temperature storage led to much lower results. Taking the lower reference limit as 50%, most would have been defined as "abnormal," and a misdiagnosis of nuWD or hemophilia A could easily arise. ABO classification and age were associated with FVIII and nuWF levels, but neither was associated conclusively with relative loss of plasma FVIII coagulant and nuWF caused by the cold-activation phenomenon. We advise laboratories following current NCCLS guidelines not to store or transport whole blood samples for FVIII and nuWF testing at 2degreesC to 4degreesC because of the risk of misdiagnosing nuWD or hemophilia A. Storage and transport at ambient temperature seem acceptable and provide results comparable to freshly centrifuged samples.