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Thrombin Mixing Study

Test ID: 


CPT code:



Thrombin Clotting Time (TCT)

Clinical Use:

Help to determine the presence of an inhibitor.

Test Information:

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 which 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 and extended thrombin time.
If the TT on the 1:1 mixture is corrected to normal or near normal, fibrinogen deficiency or dysfunction may be confirmed by the combination of the clot-based fibrinogen activity assay and the fibrinogen antigen immunoassay. Failure of the 1:1 mix to correct suggests the presence of an inhibitor. Heparin can be ruled out through the addition of a heparin neutralizer. If no heparin is present, a fibrinogen activity and fibrinogen antigen may be used to confirm and quantitate afibrinogenemia, hypofibrinogenemia, and dysfibrinogenemia. If disseminated intravascular coagulation (DIC) is suspected, D-dimer and/or FDP assays may be used. If a bovine thrombin (anti-IIa) inhibitor is suspected, a thrombin time using human-derived thrombin as the reagent should be performed. If a paraprotein disorder is suspected, a serum protein electrophoresis may be performed

Specimen Type:

Plasma, frozen

Requested Volume: 

2 mL

Minimum Volume: 

1 mL

Container Type: 

Blue-top (sodium citrate) tube

Patient Preparation: 

Avoid warfarin (Coumadin®) therapy for two weeks and heparin therapy for two days prior to the test. 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. 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 frozen purple tube with screw cap. Freeze immediately and maintain frozen until tested.

Storage Instructions:


Rejection Criteria

Gross hemolysis; clotted specimen; frozen specimen thawed in transit; improper labeling

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