Stage III fibrinogen defects can be detected by the TT test. It can detect DIC and hypofibrinogenemia and may also be used for monitoring streptokinase therapy. The TT test may be used to evaluate the presence of direct thrombin inhibitor anticoagulants in the blood. The test actually measures the time needed for plasma to clot when thrombin is added. Normally, a clot forms rapidly; if it does not, a stage III deficiency is present (Figure 2.3). A TT test is often included as part of a panel for coagulation defects.

12.0–19 seconds (varies widely by laboratory)

Check with your laboratory for values.

1. Use the procedure for two-tube specimen collection to anticoagulate a 7-mL venous blood sample with sodium citrate and put on ice. Take care not to contaminate the specimen with heparin from IV apparatus or other sources. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered.

2. Ensure that the specimen is tested within 2 hours, or it must be frozen for later testing.

1. Prolonged TT occurs in:

   1. Hypofibrinogenemia

   2. Therapy with heparin or heparin-like anticoagulants

   3. DIC

   4. Fibrinolysis

   5. Multiple myeloma

   6. Presence of large amounts of FSPs or FDPs, as in DIC

   7. Uremia

   8. Severe liver diseases

2. Shortened TT occurs in:

   1. Hyperfibrinogenemia

   2. Elevated Hct (>55%)

3. Therapy with plasminogen activators—streptokinase, urokinase, or tissue plasminogen activator (tPA). Anticoagulant therapy is an attempt either to prevent thrombus formation or to promote thrombus lysis. The type and location of the thrombus usually determine the type of anticoagulant to be administered and the treatment protocol. The newest treatment for life-threatening thrombus formation uses plasminogen activators to accelerate fibrinolysis, which is the enzymatic dissolution of already organized clots (Figure 2.4). The action of some of these agents produces a lytic state that can be monitored by the TT.

Although several tests are sensitive to the effects of thrombolytic drugs, many require lengthy assay procedures or special techniques. Of the laboratory procedures that have been recommended (PT, TT, aPTT, quantitative fibrinogen, euglobulin clot lysis, and plasminogen levels), the TT has become widely accepted because it is fast and practical, does not require special equipment, and can detect the decrease in fibrinogen levels as well as the presence of fibrin and FDPs.

The half-life of these activators is relatively short (10–90 minutes); therefore, the antidote for overdose is to hold giving the next dose.

Pretest Patient Care

1. Explain test purpose and procedure.

2. If possible, ensure that no heparin is taken for 2 days before testing.

3. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

1. Heparin prolongs TT. Interpret test results within this context.

2. Plasminogen activator therapy prolongs TCT.

3. see Appendix E for drugs that affect test outcomes.