Hemostasis Coagulation Practice Test 2026 – Comprehensive Exam Prep

Chromogenic assays rely on an enzymatic reaction that produces a color change in a substrate. In this setup, a fixed amount of Factor Xa is added to the patient’s plasma along with a chromogenic substrate. The color development reflects how much Xa remains active (or how much the activity is inhibited by factors in the plasma, such as heparin in an anti-Xa assay). The resulting color is measured spectrophotometrically, and the intensity correlates with the specific coagulation activity or inhibitor level being assessed. This contrasts with clot-based tests, which measure time to clot formation, and immunologic tests like ELISA or other immunoassays that rely on antibodies rather than enzymatic color development.