Chromogenic Substrate Clotting Factor Assay

**Semantic type:** Laboratory Procedure

**Definition:** A reagent containing purified coagulation factors (FIXa, FX and thrombin) in optimal concentrations is added to test plasma in the first stage, which does not rely on the extrinsic or intrinsic initiation pathways as the thrombin activates FVIII. The amount of FXa generated in the first stage is measured by its action on a specific chromogenic substrate, which releases a chromophore upon cleavage. The color intensity produced is directly proportional to the amount of FXa, which in turn is directly proportional to the FVIII activity in the sample.

**Synonyms:** - Chromogenic Substrate Assay - Chromogenic Substrate Assay