STABILITY OF CANINE FACTOR-VIII AND VON-WILLEBRAND-FACTOR ANTIGEN CONCENTRATION IN THE FROZEN STATE

The stability of factor Vm and von Willebrand factor antigen concentra tion in the frozen state was assessed. Citrated plasma was obtained fr om 10 healthy, mixed breed dogs and separated into 300 mu l aliquots. One aliquot was assayed immediately and the others were frozen at eith er -20 degrees C or -70 degrees C. The activity of factor Vm and the c oncentration of von Willebrand factor antigen were measured after one week and one, two, three, four, five, six, eight and 10 months of stor age. There were minor changes in both variables, particularly after fo ur months, resulting in a decrease in the activity of factor WI and an increase in the concentration of von Willebrand factor antigen. The c hanges were more pronounced at -20 degrees C. However, both factors re mained relatively stable for the whole period.