[2] The thrombin time compares the rate of clot formation to that of a sample of normal pooled plasma.

[3] In blood samples suspected to contain heparin, a substance derived from snake venom called batroxobin[4] (formerly reptilase) is used for comparison to thrombin time.

Thrombin time can be prolonged by heparin, fibrin degradation products, and fibrinogen deficiency or abnormality.

[5] Whole blood is taken with either citrate or oxalate additive (if using the vacutainer system, this is a light blue top tube).

[6] Laboratories usually calculate their own ranges, based on the method used and the results obtained from healthy individuals from the local population.