A patient on anticoagulants has a prolonged thrombin time but a normal fibrinogen level. This pattern may indicate which possibility?

A patient on anticoagulants has a prolonged thrombin time but a normal fibrinogen level. This pattern may indicate which possibility?

• A. Heparin Contamination
• B. Vitamin K Deficiency
• C. Factor VII Deficiency
• D. Factor VIII Deficiency

Answer: (A)

Thrombin time measures the final step of clot formation—the conversion of fibrinogen to fibrin by thrombin. If this test is prolonged but the fibrinogen level is normal, the issue is likely something that interferes with thrombin activity rather than a lack of fibrinogen. Heparin in the sample inhibits thrombin, which would prolong the thrombin time without changing how much fibrinogen is present. Among the given options, this makes heparin contamination the most plausible explanation. Vitamin K deficiency would mainly lengthen PT (and sometimes aPTT) by reducing vitamin K–dependent factors, not by extending the thrombin step alone. Factor VII deficiency affects PT, and Factor VIII deficiency affects the intrinsic pathway (aPTT) rather than the thrombin time. So they don’t fit the pattern of prolonged thrombin time with a normal fibrinogen level.

Thrombin time measures the final step of clot formation—the conversion of fibrinogen to fibrin by thrombin. If this test is prolonged but the fibrinogen level is normal, the issue is likely something that interferes with thrombin activity rather than a lack of fibrinogen. Heparin in the sample inhibits thrombin, which would prolong the thrombin time without changing how much fibrinogen is present. Among the given options, this makes heparin contamination the most plausible explanation.

Vitamin K deficiency would mainly lengthen PT (and sometimes aPTT) by reducing vitamin K–dependent factors, not by extending the thrombin step alone. Factor VII deficiency affects PT, and Factor VIII deficiency affects the intrinsic pathway (aPTT) rather than the thrombin time. So they don’t fit the pattern of prolonged thrombin time with a normal fibrinogen level.