Stability of canine factor VIII and von Willebrand factor antigen concentration in the frozen state

The stability of factor VIII and von Willebrand factor antigen concentration in the frozen state was assessed. Citrated plasma was obtained from 10 healthy, mixed breed dogs and separated into 300 microliters aliquots. One aliquot was assayed immediately and the others were frozen at either -20 degrees C or -70 degrees C. The activity of factor VIII and the concentration of von Willebrand factor antigen were measured after one week and one, two, three, four, five, six, eight and 10 months of storage. There were minor changes in both variables, particularly after four months, resulting in a decrease in the activity of factor VIII and an increase in the concentration of von Willebrand factor antigen. The changes were more pronounced at -20 degrees C. However, both factors remained relatively stable for the whole period.