The thrombin clotting time (TCT, plasma thrombin time) test is used to evaluate the common final pathway of the coagulation sequence. Preformed thrombin (coagulation factor IIa), usually of bovine origin, can be added to the blood sample to convert fibrinogen (factor I) directly to a fibrin clot. Because the test bypasses the intrinsic and extrinsic pathways, deficiencies in either one do not affect the TCT (see Fig. 2-1).

Thrombin-induced clotting is very rapid, and the test result can be standardized to any desired normal value (usually 10 to 15 seconds). The TCT is prolonged if fibrinogen levels are below 100 mg/dL (normal: 150 to 400 mg/dL), if the fibrinogen present is functioning abnormally, or if fibrinogen inhibitors (e.g., streptokinase, urokinase) are present (see below). In all of these conditions, the PT and PTT also are prolonged.³³

• 10 to 15 seconds (Values vary among laboratories.)

• A fibrinogen level of less than 100 mg/dL (SI units, 1.00 g/L) (normal: 150 to 400 mg/dL [SI units, 1.50 to 4.00 g/L) prolongs the TCT.
• Abnormally functioning fibrinogen prolongs the TCT.
• Fibrinogen inhibitors such as streptokinase and urokinase prolong the TCT.
• Traumatic venipunctures and excessive agitation of the sample may alter results.

• Confirmation of suspected DIC as indicated by a prolonged TCT
• Detection of hypofibrinogenemia or defective fibrinogen
• Monitoring of effects of heparin or fibrinolytic therapy (e.g., with streptokinase)

Nursing Care Before the Procedure

In general, client preparation is the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

• If the individual is receiving anticoagulant therapy, the time and the amount of the last dose should be noted.

A venipuncture is performed and the sample collected in a light-blue-topped tube. Traumatic venipunctures and excessive agitation of the sample should be avoided.

Nursing Care After the Procedure

Care and assessment after the procedure are essentially the same as for any study involving the collection of a peripheral blood sample.

• Because the client may have a coagulation deficiency, maintain digital pressure directly on the puncture site for 3 to 5 minutes after the needle is withdrawn.
• Inspect the site for excessive bruising after the procedure.