Thrombin Clotting Time (TCT)
Diagnose fibrinogen deficiency, both congenital and acquired; identify heparin contamination of samples and direct thrombin inhibitor therapy.
Thrombin time will be extended when functional fibrinogen levels are <100 mg/dL. This can occur due to congenital conditions including afibrinogenemia (complete lack of fibrinogen), hypofibrinogenemia, and in dysfibrinogenemia, a condition characterized by the presence of dysfunctional fibrinogen. Acquired conditions can lead to diminished fibrinogen levels and extended thrombin times include liver disease, renal disease, disseminated intravascular coagulation (DIC), amyloidosis, malignancy, and thrombolytic therapy. Thrombin inhibitors including heparin, argatroban, and hirudin will cause an extended thrombin time.
Blue-top (sodium citrate) tube
Ideally the patient should not be on anticoagulant therapy. Avoid warfarin (Coumadin®) therapy for two weeks prior to the test and heparin, direct Xa, and thrombin inhibitor therapies for about three days prior to testing. Do not draw from an arm with a heparin lock or heparinized catheter.
Citrated plasma samples should be collected by double centrifugation. Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate. Evacuated collection tubes must be filled to completion to ensure a proper blood to anticoagulant ratio. The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples, except when using a winged blood collection device (ie, “butterfly”), in which case a discard tube should be used. When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternate anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells. Deliver to a plastic transport tube, cap, and recentrifuge for 10 minutes. Use a second plastic pipette to remove the plasma, staying clear of the platelets at the bottom of the tube. Transfer the plasma into a PP transpak frozen purple tube with screw cap. Freeze immediately and maintain frozen until tested.
Severe hemolysis; improper labeling; clotted specimen; specimen diluted with IV fluids; samples thawed in transit; improper sample type; sample out of stability