Reptilase Time

The reference range for reptilase time depends on the test kit or instrumentation used in the laboratory but is usually below 20 seconds (ie, 15-19 seconds). Healthy infants aged 6 months or younger may have a slightly prolonged reptilase time by 2-3 seconds.

Similar to thrombin time (TT), normal reptilase time excludes abnormalities in the fibrin formation process of the coagulation cascade; however, the test is not sensitive to heparin (low-molecular-weight heparin or unfractionated heparin) or direct antithrombin inhibitors (eg, hirudin, bivalirudin, argatroban, dabigatran).

Normal reptilase time with prolonged TT indicates that the specimen contains drugs or heparinlike molecules with antithrombin activity. ^[1]

Prolonged reptilase time suggests the following fibrinogen abnormalities:

• Severe hypofibrinogenemia or afibrinogenemia (congenital or acquired)

• Congenital or acquired dysfibrinogenemia

• Moderate hyperfibrinogenemia (>7 g/L) ^[2]

Reptilase time testing also reveals impairment of fibrin formation, including the following:

• Disseminated intravascular coagulation (presence of fibrin degradation products, D-dimer)

• Abnormal circulating proteins due to amyloidosis, multiple myeloma

See the list below:

• Specimen - Citrated plasma

• Collection - Tube with 3.2% sodium citrate, blue top

• Centrifugation - 2000-2500 g for 15 minutes or similar regime to produce platelet poor plasma

• Storage - 8 hours at room temperature (samples with heparin up to 2 h) or plasma sample should be frozen within 1-2 hours; specimen stable for one month at -20 º C, 6-9 months at -80 º C.

Description

Reptilase time is a specific coagulation test designed to assess fibrin formation from fibrinogen in plasma. Reptilase time is modified TT when thrombin is replaced with the enzyme reptilase, also known as batroxobin, purified from snake venom. In contrast to thrombin, reptilase cleaves only fibrinopeptide A (not fibrinopeptide B) during fibrin clot formation. Reptilase time testing is performed as the next step to evaluate abnormally prolonged activated partial thromboplastin time (PTT) or prothrombin time (PT) with concomitantly prolonged TT. ^{[3, 1]} \

Reptilase time and TT have, in many instances, been replaced by the clotting-based functional fibrinogen assay in the assessment of fibrinogen. ^[4]

Indications/Applications

Unexplained prolongation of PT or PTT with prolonged TT is an indication for testing reptilase time.

A study by Ha et al indicated that when measuring functional fibrinogen in plasma, a batroxobin-based assay can serve as a good alternative to the traditional thrombin-based fibrinogen test. Bivalirudin and other anticoagulants that target thrombin were found not to interfere with the batroxobin-based test. ^[5]

Considerations

Low albumin levels (< 30 g/L) in plasma sample can cause reptilase time prolongation due to delayed fibrin polymerization. ^[6]