A Novel Fibrinogen Assay Using Recombinant Batroxobin and Carboxymethyl Chitosan: Carboxymethyl Chitosan Stimulates the Enzymatic Activity of Recombinant Batroxobin.

Background: The Clauss assay is widely used to quantify blood fibrinogen levels in clinical laboratories. However, by relying on thrombin as the main reagent, the Clauss assay is susceptible to interference from thrombin inhibitors, such as heparin or direct thrombin inhibitors. Here, we developed an innovative fibrinogen assay utilizing both recombinant batroxobin (rBat) and carboxymethyl chitosan (CMCS).

Methods: Various biopolymers were tested to identify a suitable candidate that could enhance rBat-induced fibrin clot formation. Chromogenic substrate hydrolysis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that CMCS potentiated rBat activity. Consequently, we formulated a novel fibrinogen assay reagent, ANYFIB.C, comprising rBat and CMCS. We compared ANYFIB.C fibrinogen with an established reagent (HemosIL fibrinogen-C) with 96 clinical samples using an ACL-TOP 700 coagulation analyzer. We also evaluated the interfering effects of thrombin inhibitors on fibrinogen measurements.

Results: CMCS significantly enhanced the enzymatic activity of rBat and dose-dependently reduced plasma clotting times. ANYFIB.C fibrinogen levels were comparable with those of HemosIL fibrinogen-C, with the 95% confidence intervals of the Passing-Bablok regression intercept and slope being -7.4797 to 6.0185 and 0.9581 to 1.0116, respectively. No significant interference was observed with heparin concentrations up to 10 U/mL or dabigatran concentrations up to 600 μg/L in the ANYFIB.C fibrinogen assays. In contrast, the HemosIL fibrinogen-C reagent demonstrated inhibitory interference at dabigatran concentrations as low as 150 μg/L.

Conclusions: Our results suggest that ANYFIB.C (a mixture of CMCS and rBat) can be used to measure blood fibrinogen levels effectively and protect from thrombin inhibitor interference.