Which statement correctly differentiates thrombin time from reptilase time?

Which statement correctly differentiates thrombin time from reptilase time?

• A. Thrombin Time Is Prolonged by Heparin While Reptilase Time Is Not
• B. Reptilase Time Is Longer Than Thrombin Time in Normal Plasma
• C. Thrombin Time Measures Platelet Function
• D. Reptilase Time Directly Measures Factor VIII Activity

Answer: (A)

Thrombin time and reptilase time both assess how fibrin forms from fibrinogen, but they rely on different enzymes. Thrombin time uses thrombin to cleave fibrinogen into fibrin, so anything that inhibits thrombin—such as heparin or direct thrombin inhibitors—prolongs the test. Reptilase time uses a venom-derived enzyme, reptilase, to convert fibrinogen to fibrin without depending on thrombin, and this enzyme is not inhibited by heparin, so the test remains unaffected by heparin. That’s why this differentiates the two: thrombin time is prolonged in the presence of heparin, whereas reptilase time is not. The other statements misstate what each test measures—thrombin time is not a measure of platelet function, and reptilase time does not directly reflect a specific factor activity such as Factor VIII.

Thrombin time and reptilase time both assess how fibrin forms from fibrinogen, but they rely on different enzymes. Thrombin time uses thrombin to cleave fibrinogen into fibrin, so anything that inhibits thrombin—such as heparin or direct thrombin inhibitors—prolongs the test. Reptilase time uses a venom-derived enzyme, reptilase, to convert fibrinogen to fibrin without depending on thrombin, and this enzyme is not inhibited by heparin, so the test remains unaffected by heparin. That’s why this differentiates the two: thrombin time is prolonged in the presence of heparin, whereas reptilase time is not. The other statements misstate what each test measures—thrombin time is not a measure of platelet function, and reptilase time does not directly reflect a specific factor activity such as Factor VIII.