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85635 |
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C |
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Description |
The reptilase time measures the conversion of fibrinogen to fibrin clot by reptilase (Batroxobin, Atroxin), a thrombin-like enzyme derived from the venom of the fer-de-lance (barba amarilla,Bothrops atrox) a poisonous snake of South and Central America and the West Indies. In contrast to thrombin, which cleaves fibrinopeptides A, AP, and B from the fibrinogen molecule, reptilase only cleaves fibrinopeptides A and AP. The resulting fibrin monomers polymerize end-to-end to form a fibrin clot. Reptilase has no fibrinolytic activity, does not activate plasminogen, and in not inhibited by antifibrinolytics or heparin. The reptilase time is used in the evaluation of a prolonged APTT, specifically to exclude the presence of dysfibrinogenemia.
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Preparation |
No specific patient preparation is required. However, since lipemia may interfere with photo-electric measurements of clot formation, specimens should not be obtained after a meal. |
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Requirements |
Citrated, platelet-poor plasma is used for the reptilase time. This is prepared from venous blood collected by venipuncture or from an indwelling catheter is used for the APTT. The blood is collected into 129 mM (3.8%) trisodium citrate at a ratio of 9:1. The blue-top tube automatically fills to the correct volume; spurious results may occur if this ratio is not maintained. A traumatic venipuncture can activate coagulation factors, leading to a shortened APTT. The APTT must be performed within two hours after sample procurement. Frozen plasma stored at -70oC is acceptable if the specimen is spun properly to remove all platelets and promptly frozen. |
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Methodology |
The reptilase time is performed at 37oC. Citrated plasma is added to a solution of reptilase prewarmed to 37oC and the time required for the formation of fibrin monomers is determined visually, mechanically, or opto-electronically. The reptilase time is reported in seconds.
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and Critical Limits |
11 - 14 seconds. |
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The reptilase time is not inhibited by thrombin inhibitors (heparin, hirudin, anti-thrombin antibodies) or by antithrombin III. Myeloma proteins reactive with thrombin may prolong the reptilase time. Fibrin degradation products (FDPs) slightly prolong the reptilase time. |
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Hypofibrinogenemia and dysfibrinogenemia are the usual causes of a prolonged reptilase time. Prolongation of both the thrombin time and reptilase time suggests hyop- or dysfibrinogenemia. A prolonged APTT and normal reptilase time indicates that heparin is the cause of the prolonged APTT. |
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References |
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