Medical Laboratory Scientist (MLS) ASCP Practice Exam

The evaluation of fibrinogen levels in heparinized patients is most accurately performed using reptilase time. Reptilase is a snake venom enzyme that converts fibrinogen to fibrin independently of thrombin. This characteristic makes it particularly useful in situations where heparin is present, as heparin inhibits thrombin activity and can interfere with other tests that rely on thrombin for fibrin formation.

In this context, reptilase time can provide a clear indication of fibrinogen levels, as it does not get affected by heparin and directly assesses the ability of fibrinogen to be converted to fibrin. The reptilase time will be prolonged if the fibrinogen concentration is low or if there are abnormalities in fibrinogen function.

In contrast, prothrombin time and activated partial thromboplastin time are both affected by the presence of heparin. They measure different pathways of the coagulation cascade but can give misleading results regarding fibrinogen levels when heparin is present. Thrombin time, while it does measure fibrinogen conversion, is similarly affected by heparin, rendering it less useful in these patients.

Thus, reptilase time stands out as the most