Influence of factor VIII:C and factor IX activity in plasmas of haemophilic dogs on the activated partial thromboplastin time measured with two commercial reagents

The present study is based on 145 plasma samples with a reduced activity of factor VIII:C (range: 0.009-0.62 IU mL(-1)) and 28 samples with a reduced factor IX activity (range: 0.035-0.55 IU mL(-1)). The samples were collected from dogs with haemophilia A (n = 22) or haemophilia B (n = 3), some of these during substitution therapy. For all samples the activated partial thromboplastin time (APTT) was measured with two commercial reagents containing kaolin as a contact activator. In each case, the deficiency of factor VIII:C or IX was reflected in abnormal results of the APTT. This was true for both reagents. A significant correlation (P < 0.001) was found between factor VIII:C activity and APTT (reagent 1, Pathromtin(R); Spearman's rank correlation coefficient, r(S) = -0.731, reagent 2, PTT-Reagenz; r(S) = -0.875) as well as between factor IX activity and APTT (reagent 1, r(S) = -0.819; reagent 2, r(S) = -0.955]. In each case, the relationship between coagulation factor activity and APTT could be proven most precisely by geometric regression. The results of this study illustrate the applicability of commercial APTT test kits as a sensitive screening test of factor VIII:C and IX deficiencies in canine plasma.