Coagulation Factors
Underestimation of the clotting activity of individual coagulation factors is expected in patients taking NOAC. For example, factor VIII activity can be underestimated. Coagulation factors might be underestimated in patients taking anti-factor Xa drugs when measured with chromogenic assays.
Fibrinogen
The final step of the coagulation cascade is the conversion of fibrinogen to fibrin. Thrombin converts fibrinogen to fibrin, and a fibrin clot is formed that is stabilized by the presence of factor XIII. The thrombin time test measures the concentration and activity of fibrinogen.
Fibrinogen may be underestimated in dabigatran patients, but the effect is method-dependent. Before measuring fibrinogen in patients on NOAC, laboratories should check with the manufacturer for any possible interference.
