Reptilase time explained

Reptilase time
Purpose:	blood test used to detect deficiency or abnormalities in fibrinogen

Reptilase time (RT) is a blood test used to detect deficiency or abnormalities in fibrinogen,^{[1] [2]} especially in cases of heparin contamination.

Reptilase, an enzyme found in the venom of Bothrops snakes, has activity similar to thrombin. Unlike thrombin, reptilase is resistant to inhibition by antithrombin III. Thus, the reptilase time is not prolonged in blood samples containing heparin, hirudin, or direct thrombin inhibitors, whereas the thrombin time will be prolonged in these samples. Reptilase also differs from thrombin by releasing fibrinopeptide A, but not fibrinopeptide B, in its cleavage of fibrinogen.

Causes of prolonged thrombin time^[3] ! Reptilase time !! Cause !! Further workup indicated

Normal	Heparin, hirudin, or direct thrombin inhibitor	Human TT and/or heparin assays
Prolonged	Hypo- or afibrinogenemia	Fibrinogen quantification
	Dysfibrinogenemia	Fibrinogen activity assay
	Fibrin(ogen) split products (FSP)	FSP or D-dimer quantification

Notes and References

1. Van Cott EM, Smith EY, Galanakis DK . Elevated fibrinogen in an acute phase reaction prolongs the reptilase time but typically not the thrombin time . . 118 . 2 . 263–8 . August 2002 . 12162688 . 10.1309/WUB3-72JT-E50M-EU8J . free .
2. Johnson PJ, White Y, Woolf IL, Williams R . Reptilase time in cirrhosis and hepatocellular carcinoma . Br Med J . 2 . 6091 . 869–70 . October 1977 . 200301 . 1631704 . 10.1136/bmj.2.6091.869-a.
3. Web site: Test ID: RTSC. Reptilase Time, Plasma. Mayo Clinic laboratories. 2021-02-25.