The Thrombin Time (TT) assay is based on the ability of thrombin to catalyse the polymerisation of fibrinogen into a fibrin clot. The test is often used when routine screening results (mainly the APTT) are extended.
A normal thrombin time excludes abnormalities in the fibrin formation process of the coagulation cascade. A shortened thrombin time is rare and is observed in patients treated with certain forms of hereditary dysfibrinogenemia. A prolonged thrombin time indicates a fibrinogen abnormality, impairment of fibrin formation, and/or a thrombin inhibitory effect.
Current laboratory (adult, M/F) normal ranges are as follows:
- 15.4 – 19.4 seconds
The volume of blood in coagulation samples must lie within the volume range as indicated by the size of the black fill arrow present on tubes. Volumes above or below the arrow will result in sample rejection to ensure validity of results.
- Urgent: 1 hour
- Routine: 4 hours
Age of sample
Samples will be rejected if received more than 8 hours after venepuncture.
- 1 blue top (sodium citrate) sample.
- All coagulation tubes must be adequately filled (see above).
- All coagulation tubes must be mixed several times by gentle inversion immediately after venepuncture. Mixing the sample with the anticoagulant stops the sample clotting within the tube.
- It is not possible to provide results on haemolysed, or lipaemic samples. These will be rejected with the appropriate comment.
- Sample tubes that have expired cannot be accepted.
- Coagulation Lab, James Cook University Hospital, Marton Road, TS4 3BW
- Coagulation Lab, Friarage Hospital, Northallerton, DL6 1JG