If reptilase time is normal while thrombin time is prolonged, which condition is most likely?

• A. Presence of fibrin degradation products
• B. Dysfibrinogenemia
• C. Hypoplasminogenemia
• D. Presence of heparin

Answer: (D)

Testing concept: using reptilase time versus thrombin time to distinguish heparin effect from fibrinogen-related problems. Thrombin time measures how long it takes for thrombin to convert fibrinogen to fibrin and is susceptible to inhibition by heparin. If heparin is present, thrombin is inhibited and the time lengthens. Reptilase time uses a venom enzyme that also converts fibrinogen to fibrin but is not inhibited by heparin, so its measurement stays normal even when heparin is present. Therefore a normal reptilase time with a prolonged thrombin time points to heparin contamination or therapeutic heparin rather than an intrinsic fibrinogen abnormality. If the issue were a true fibrinogen problem, both tests would more likely be affected.