RT measures the conversion of fibrinogen to fibrin when added to plasma. The reagent is a thrombin-like enzyme derived from venom of Bothrops atrox. It is unaffected by heparin or hirudin.
Normal value: <20 seconds.
Use
An abnormal RT indicates an abnormality of fibrinogen, whereas a normal RT suggests heparin or hirudin as the cause of an abnormal thrombin time.
A RT evaluates prolonged PTT when heparin or hirudin contamination is suspected.
It also excludes dysfibrinogenemia.
Interpretation
Causes of Increased RT
Hypofibrinogenemia or dysfibrinogenemia
Slightly prolonged in the presence of fibrin degradation products as seen in severe DIC or pathologic fibrinolysis
Limitations
Preanalytic: partially clotted blood or hemolyzed blood, improperly filled or stored test tubes, specimens collected in wrong tubes