Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1191 page)

REPTILASE TIME (RT)
*

   Definition

   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

   Lipemic or icteric samples