Ej. Favaloro et Pa. Mehrabani, LABORATORY ASSESSMENT OF VON-WILLEBRAND-FACTOR - DIFFERENTIAL INFLUENCE OF PROLONGED AMBIENT-TEMPERATURE SPECIMEN STORAGE ON ASSAY RESULTS, Haemophilia, 2(4), 1996, pp. 218-223
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.