The prothrombin consumption time (PCT, serum prothrombin time) test measures utilization of prothrombin when a blood clot forms. Normally, the formation of a clot "consumes" prothrombin by converting it to thrombin. Individuals with deficiencies in platelets, platelet factor 3, or factors involved in the intrinsic coagulation pathway (see Fig. 2-1) are not able to convert as much prothrombin to thrombin. In such cases, excess prothrombin remains in the serum after the clot is formed, thus shortening the PCT. The PCT also may be shortened in persons receiving anticoagulant therapy or in those with DIC, hypoprothrombinemia, and cirrhosis.

Abnormal PCT results must be evaluated in relation to coagulation studies such as PT, PTT, and factor assays, to differentiate platelet factor deficiencies from clotting factor deficiencies.

• Fifteen to 20 seconds with more than 80 percent of the prothrombin consumed

• Traumatic venipunctures and excessive agitation of the sample may alter test results.
• Therapy with anticoagulants may shorten the PCT.

• Suspected deficiency of platelet factor 3 or of the clotting factors involved in the intrinsic coagulation pathway (i.e., factors VIII, IX, XI, and XII), as indicated by a shortened PCT
• Suspected DIC, as indicated by a shortened PCT
• Monitoring of effects on hemostasis of conditions such as liver disease and protein deficiency

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 client 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 red-topped tube. As with other coagulation studies, 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coagulation deficiency, maintain digital pressure directly on the puncture site for 3 to 5 minutes after the needle is withdrawn.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.