Most labs will be familiar with fibrinogen testing. Fibrinogen (factor I) is often measured to assess patients who may have afibrinogenemia or hypofibrinogenemia. Decreased levels of fibrinogen are found in advanced liver disease, patients treated with TPA, patients with disseminated intravascular coagulation (DIC), and patients with genetic mutations that reduce fibrinogen production.
When fibrinogen is activated to fibrin, a clot is formed. And while fibrinogen can be useful to measure, the degradation of fibrin is a more specific test for assessing fibrinolysis. Fibrin is a polymer that, when broken down, degrades into so-called 'fibrin degradation products' (FDP). Measuring FDP became available in the 1990s. FDP was found to be a very good lab test to rule out thrombosis (blood clots). Unfortunately, a positive FDP is not a very good predictor of thrombosis (i.e., the test has a poor positive predictive value). But a negative FDP is a good test for ruling out thrombosis (it has a good negative-predictive value).
