Determination of Prothrombin in Feline Plasma

Determination of the major common pathway protein prothrombin, a vitamin K-dependent protein synthesized in the liver, may be useful for identifying coagulopathies in cats with liver disease or vitamin K antagonism. In people with liver disease, prothrombin is more commonly and more severely decreased than other procoagulant proteins. The purpose of this study was to evaluate a commercial chromogenic assay (DiaPharma Group, West Chester, Ohio, USA) for the determination of prothrombin activity in plasma from healthy cats. The method involves the cleavage of prothrombin by Ecarin, a nonphysiologic enzyme activator that cleaves prothrombin to meizothrombin, which then interacts with a chromogenic substrate. Citrated (n = 20) and EDTA (n = 37) plasma samples from clinically healthy cats were tested using 100-fold and on occasion 200-fold dilutions. The assay was run according to manufacturer's specifications and the relative percentage prothrombin activity was calculated using standard curves generated from a feline citrated plasma pool and human reference plasma. Slope and regression values (r = .998) were similar for feline and human samples, suggesting that Ecarin cleaves prothrombin in both feline and human plasma in an analogous manner. The correlation between results obtained using feline vs human reference plasma was high for both citrated (r = .910) and EDTA samples (r = .998). When prothrombin was determined using human reference plasma, results from citrated feline plasma samples were 75.7% ± 9.0% of normal compared to 91.6% ± 7.0% of normal when the feline standard curve was used. Similar results were obtained using EDTA plasma. Our results indicate that the prothrombin chromogenic assay may be useful for evaluating one component of the hemostatic pathway in feline plasma. The prothrombin chromogenic assay utilizes routine instrumentation, requires small sample volume (5 μL/assay), and may be used on EDTA plasma. To optimize sensitivity, the assay should be run using a standard curve generated with a feline plasma pool.