Temporal variation and factors affecting measurement of canine von Willebrand factor.

OBJECTIVE To determine whether canine plasma von Willebrand factor (vWf) varies between and within individuals over time and with different blood sample collection and processing procedures. ANIMALS 26 adult dogs and 6 pups. PROCEDURE Blood was obtained from the jugular or cephalic vein daily for 8 to 19 days and weekly for 9 to 23 weeks in adult dogs and periodically up to 180 days of age in pups. Temporal variation in vWf concentration and the effect of vascular occlusion, venipuncture site, lipemia, hemolysis, anticoagulant, storage time, freeze-thawing, and centrifugation speed on plasma vWf concentration, measured by ELISA, were determined. RESULTS Plasma vWf concentration varied over time. In dogs with mean vWf concentration > or = 79 U/dl, the largest intraindividual range in vWf spanned 64 U/dl with daily and 53 U/dl with weekly sample collection. In dogs with mean vWf concentration < or = 24 U/dl, the largest individual variation was 12 U/dl with daily and weekly sample collection. In dogs with mean vWf concentration > or = 53 and < or = 74 U/dl, the largest intraindividual range spanned 35 U/ dl. Mean vWf concentration of pups from 3 to 180 days of age did not change. Sample hemolysis decreased mean vWf by 37%. Mean vWf concentration was 9% higher in cephalic than jugular vein samples (P = 0.056). Other sample collection/preparation procedures did not affect vWf concentration. CONCLUSION There was substantial temporal variation in vWf concentration within individual dogs. CLINICAL RELEVANCE Multiple tests may be necessary to obtain a reliable estimate of vWf concentration in dogs.