The most widely used technique for determination of fibrinogen concentration is the Clauss fibrinogen (FIBClauss) assay, which measures the clotting time of plasma after addition of excess thrombin. More recently, the PT-derived fibrinogen (FIBPT) assay has been
developed, based on the relationship between fibrinogen concentration and the kinetics of clot formation during the prothrombin time. The objective of this study was to compare the fibrinogen concentration determined by the FIBClauss and FIBPT assays in citrated plasma samples from
healthy dogs (n = 40), monkeys (n = 40), rabbits (n = 26), and rats (n = 58) by using an automated coagulation analyzer. Results of a t test analysis indicated that the mean plasma fibrinogen concentrations measured by the 2 assays for all 4 species were
significantly different. According to Pearson correlation coefficients, the FIBPT assay displayed a high correlation (0.93 to 0.98) with the FIBClauss assay for all species. When the FIBPT and FIBClauss assays were compared by using Deming regression, positive or negative constant and proportional
biases emerged for all species. Intra- and interassay coefficients of variation for the FIBPT and FIBClauss assays were 0.8% to 2.3% and 1.8% to 7.4%, respectively. In conclusion, the FIBPT assay is a rapid and economical method for estimating fibrinogen concentration in plasma samples from
dogs, monkeys, rabbits, and rats. However, it should not be used without restriction. Further studies are required to investigate the performance of this assay in animals with various pathologic states, including coagulopathy, dysfibrinogenemia, and hypo- or hyperfibrinogenemia.