Thrombin Time

Thrombin Time

Normal Values
7.0–12.0 seconds. However, “normally” can vary widely according to different laboratories’ interpretations.

Explanation of Test
Stage III fibrinogen defects can be detected by thrombin time. It can detect DIC and hypofibrinogenemia and may also be used for monitoring streptokinase therapy. The test actually measures time needed for plasma to clot when thrombin is add. Normally, a clot will form rapidly; if it does not, a fibrinogen deficiency is present (Fig. 1).

Procedure
With the procedure for two-tube specimen collection, a 7-ml venous blood sample is anticoagulated with sodium citrate and put on ice.

Clinical Implications
1. Prolonged TT time occurs in
• Hypofibrinogenemia
• Therapy with heparin or heparinlike anticoagulants
• Disseminated intravascular coagulopathy (DIC)
• Fibrinolysis
• Multiple myeloma
• The presence of large amounts of fibrin or fibrinogen breakdown products (FBPs)
• Uremia
• Severe liver diseases
2. Shortened thrombin time occurs in
• Hyperfibrinogenemia
• Elevated hematocrit (> 755%)
Clinical alert
Thrombin time is severely prolonged in the presence of afibrinogenemia (< 80 mg/dl of fibrinogen).

Interfering Factors
Heparin prolongs thrombin time. Interpret test results within this context.



Patient Preparation
1. Explain test purpose and procedure.
2. If possible, no heparin should be administered for 2 days before testing.

Patient Aftercare
1. Resume normal activities and medications as ordered.
2. Interpret test outcomes and monitor appropriately. Check for excess bleeding.