Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1232 page)

   Preanalytic conditions may interfere with this test.

   Improper filling of blood collecting tube or use of wrong tubes (containing different anticoagulant than recommended or no anticoagulant)

   Clots in specimen

   Hemolysis

   Heparin contamination of blood, such as drawings from IV lines with heparin flushes (when heparin contamination is suspected, a reptilase time can be performed instead [see above])

   Hyperlipidemia may artificially prolong the thrombin time obtained by optical equipment (most modern machines). In such cases, the assay can be done on equipment that uses mechanical clotting.

   Results are unreliable in patients with high fibrinogen (>500 mg/dL).

   Patients previously exposed to bovine thrombin to arrest bleeding may develop thrombin antibodies.

   Use of various radiocontrast agents may affect test results.

THROMBOELASTOGRAM (TEG)
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   Definition

   TEG uses equipment (TEG analyzer) that records the process of blood coagulation, including fibrinolysis and platelet defects. It measures in vitro the kinetics of clot formation and dissolution by a mechanical process, which monitors very low shear elasticity changes. The different parameters represent different aspects of the patient’s hemostasis.

   Use

   The TEG is commonly used for cardiac bypass surgery, providing a rapid assessment of anticoagulation (heparin), restoration of coagulation with the use of protamine sulfate, excess fibrinolysis, and platelet function during the procedure.