Thrombin Mixing Study (Thrombin Clotting Time (TCT))

Help to determine the presence of an inhibitor.

Thrombin time will be extended when functional fibrinogen levels are <100 mg/dL.^6,7 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.⁶ Thrombin inhibitors including heparin, argatroban, and hirudin will cause and extended thrombin time.⁷

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.⁶ 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.⁶ If a bovine thrombin (anti-IIa) inhibitor is suspected, a thrombin time using human-derived thrombin as the reagent should be performed.⁶ If a paraprotein disorder is suspected, a serum protein electrophoresis may be performed.⁶

1. Adcock DM, Kressin DC, Marlar RA. Effect of 3.2% vs 3.8% sodium citrate concentration on routine coagulation testing. Am J Clin Pathol. 1997 Jan; 107(1):105-110. PubMed 8980376

2. Reneke J, Etzell J, Leslie S, Ng VL, Gottfried EL. Prolonged prothrombin time and activated partial thromboplastin time due to underfilled specimen tubes with 109 mmol/L (3.2%) citrate anticoagulant. Am J Clin Pathol. 1998 Jun; 109(6):754-757. PubMed 9620035

3. National Committee for Clinical Laboratory Standardization. Collection, Transport, and Processing of Blood Specimens for Coagulation Testing and General Performance of Coagulation Assays; Approved Guideline. 5th ed. Villanova, Pa: NCCLS; 2008. Document H21-A5:28(5).

4. Gottfried EL, Adachi MM. Prothrombin time and activated partial thromboplastin time can be performed on the first tube. Am J Clin Pathol. 1997 Jun; 107(6):681-683. PubMed 9169665

5. McGlasson DL, More L, Best HA, Norris WL, Doe RH, Ray H. Drawing specimens for coagulation testing: Is a second tube necessary? Clin Lab Sci. 1999 May-Jun; 12(3):137-139. PubMed 10539100

6. Adcock DM, Bethel MA, Macy PA. Coagulation Handbook.
Aurora, Colo: Esoterix−Colorado Coagulation; 2006.

7. Van Cott EM, Laposata M. Coagulation. In Jacobs DS, DeMott WR, Oxley DK, eds. Laboratory Test Handbook With Key Word Index. Hudson, Ohio: Lexi-Comp; 2001:327-358.

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.