Tests to measure fibrin clot. General Approach in Investigation of Haemostasis. Lecture 9:. Tests to Measure Fibrin formation. Thrombin Time TT Reptilase Time Fibrinogen Activity assay. Thrombin Time (TT). Also Called Thrombin Clotting Time (TCT).
General Approach in Investigation of Haemostasis
Thrombin Time TT
Fibrinogen Activity assay
Also Called Thrombin Clotting Time (TCT)
Commercially prepared bovine thrombin reagent at 2 NIH units/mL cleaves fibrinopeptides A and B from plasma fibrinogen to form a detectable polymer
1 WHO unit = 0.56 NIH unit
1 NIH unit = 0.324 +/- 0.073 µg
In the presence of heparin, thrombin is inhibited through the interaction of antithrombin (AT-III). However, heparin does not interfere with the ability of reptilase to cleave fibrinopeptide A from fibrinogen
Ancrod a similar enzyme from Agkistrodonrhodostoma can also be used to replace thrombin in the thrombin clotting time test.
The procedure is a determination based on fibrinogen activity, but results are converted to concentration (mg/dL) by comparison with control plasma results.
This time is then converted to mg/dL of fibrinogen by comparing these results to results obtained on a fibrinogen standard curve.
The calibration curve is prepared from the reference standard .
Make dilutions of the fibrinogen standard with Imidazole buffer as follows: 1:5, 1:10, 1:20 and 1:40. Make all transfers from the first test tube.
Perform determinations on each dilution of the fibrinogen standard as follows: