LABORATORY ASSESSMENT OF VON-WILLEBRAND-FACTOR - DIFFERENTIAL INFLUENCE OF PROLONGED AMBIENT-TEMPERATURE SPECIMEN STORAGE ON ASSAY RESULTS

The laboratory assessment of von Willebrand factor (VWF) is typically performed at specialist laboratory sites, particularly when performed as a battery of laboratory tests in a thorough workup for the diagnosi s of von Willebrand's disease (VWD). In these cases, specimens could d erive from a variety of off-site sources, including smaller laboratori es, and general clinical practitioners. Because of the potential for l ack of control by the specialist laboratory over the method of specime n handling and transport from these sources, and recent VWF methodolog ical advances, we investigated the effect of prolonged ambient tempera ture specimen storage on laboratory assay results. Thus, specimens wer e collected from 10 separate individuals, and each variably processed to provide an ideal (''control'') plasma specimen, and additional spec imens that were then stored at ambient temperature for up to 7 days. S pecifically, specimens were stored either as whole blood, or as separa ted plasma, and VWF tested in isolated plasma, post 24 h, post 48 h an d post 7 days storage. Three separate laboratory assays for assay resu lts over the 7-day storage period; however, there was a small but stat istically significant fall (P = 0.009) in VWF:CBA assay results after 7 days storage of plasma, (ii) Whole blood storage: there was no (stat istically significant) change in VWF:Ag, VWF:CBA or VWF:RC of assay re sults over the 7-day storage period, although the data suggested a tre nd towards increasing VWF:Ag over time. As a result of the change in a ssayed VWF:CBA following prolonged plasma storage, a similar small but statistically significant (P = 0.009) change (increase) in the VWF:Ag to VWF:CBA ratio was observed. This ratio has previously been determi ned to be useful in the differential diagnosis of VWD subtypes, with h igh VWF:Ag to VWF:CBA ratios potentially indicative of Type 2 VWD). Fo rtunately, the absolute magnitude of the altered ratio following prolo nged plasma storage is unlikely in practice to affect the diagnosis of VWD in most testing cases. Nevertheless, there will be occasional bor derline normal cases in whom the change in VWF:CBA, or in the calculat ed VWF:Ag to VWF:CBA ratio, may otherwise influence a clinical diagnos is of VWD. Caution is therefore suggested in the interpretation of lab oratory-derived VWF data, particularly if the specimen is derived as a n off-site referral.