CHROMOGENIC ASSAYS FOR EQUINE COAGULATION FACTORS VII, VIII:C, IX, AND X, AND C1-ESTERASE INHIBITOR

OBJECTIVES: To adapt manual human chromogenic assays for coagulation factors VII (F.VII), VIII:coagulant (F.VIII:C), IX (F.IX), and X (F.X), and C1-esterase inhibitor (C1-INH) for use with an automated analyzer, and to measure the activity of these proteins in horses. ANIMALS: 10 healthy horses were used to determine ranges for the assays. Pooled plasma for standards was collected from an additional 20 healthy horses. PROCEDURE: A computer-assisted analyzer was programmed from the manual method for commercially available human F.VII, F.VIII:C, F.IX, F.X, and C1-INH chromogenic assay kits. Standards were prepared from pooled citrated equine plasma for the F.VII, F.VIII:C, and F.X assays, and from commercial pooled citrated human plasma for F.IX and C1-INH assays. RESULTS: Mean +/- SD activities in citrated equine plasma from 10 horses were 226 +/- 19% for F.VII; 209 +/- 31% for F.VIII:C; 149 +/- 38% for F.IX; 88 +/- 12% for F.X; and 18.4 +/- 8.4% for C1-INH. Intra-assay coefficients of variation (CV) were 5.3% for F.VII; 2.1% for F.VIII:C; and 3.0% for C1-INH. Interassay CV were 5.7% for F.VII; 7.4% for F.VIII:C; 3.8% for F.IX; 14.4% for F.X; and 22.0% for C1-INH. CONCLUSIONS: Human chromogenic assay kits can be automated and used to measure F.VII, F.VIII:C, F.IX, F.X, and C1-INH activities in citrated equine plasma. CLINICAL RELEVANCE: Human chromogenic assays can be routinely used to measure F.VII, F.VIII:C, F.IX, F.X, and C1-INH in horses, and may be useful in evaluation of horses with disorders of hemostasis.