Introduction
The Reptilase time is a functional clotting assay based upon the enzymatic activity of Batroxobin a venom isolated from the snake Bothrops atrox and which cleaves Fibrinogen at Arg16-Gly17 releasing Fibrinopeptide A (FpA) and generating Fibrin. In contrast Thrombin cleaves both Fibrinopeptide A and Fibrinopeptide B from Fibrinogen to generate the Fibrin clot. The Reptilase time is very similar to the Thrombin time but Thrombin is replaced by Batroxobin [Reptilase].
Ancrod a similar enzyme from Agkistrodon rhodostoma can also be used to replace Thrombin in the Thrombin clotting time test.
The cDNA for Batroxobin has been cloned and a recombinant version has been developed that has similar biochemical properties to the native Batroxobin.
Principles
Reptilase is added to citrated platelet poor plasma and the clotting time measured. The test requires no added Phospholipid or Calcium.
Method
| Components | Explanation |
|---|---|
| Platelet poor plasma | See pre-analytical variables |
| Reptilase solution | Reptilase re-constituted according to the manufacturer’s instructions. |
Interpretation
The Reptilase time is rarely performed in isolation and therefore, the results of this test should be considered together with other tests and in particular the Thrombin time. A prolonged Reptilase time is seen in:
| Disorder | Explanation |
|---|---|
| Inherited and Acquired Hypofibrinogenaemia | A low Fibrinogen (usually <1.0g/L) will lead to a prolongation of both the Thrombin time and the Reptilase time. |
| Inherited Dysfibrinogenaemia | Most dysfibrinogenaemias will lead to a prolongation of both the Thrombin time and the Reptilase time. However, in some cases depending upon the site of the mutation - only one or other of the two tests may be abnormal. |
| Following Thrombolytic therapy due to the high levels of FDPs. DIC with elevated levels of FDPs |
High levels of FDPs lead to defective fibrin polymerisation and therefore, prolongation of the both the Thrombin and Reptilase times. The Thrombin and Reptilase times may also be prolonged in DIC due to hypofibrinogenaemia. |
| Hypoalbuminaemia | A low serum albumin may be associated with a prolongation of both the Thrombin time and Reptilase time. This appears to be due to an in vitro phenomenon and correction of the low albumin either in vitro or in vivo corrects the abnormality. This problem was originally reported in patients with nephrotic syndrome but has also been reported in patients with HIV. |
| Liver disease | The Thrombin time and Reptilase time are often prolonged in patients with liver disease due to both hypofibrinogenaemia, elevated FDPs, and an acquired dysfibrinogenaemia due to abnormalities of Fibrinogen sialic acid content. |
| Neonate | Neonatal Fibrinogen differs from adult Fibrinogen in its sialic acid content. As a consequence the Reptilase and Thrombin times may be physiologically prolonged. A similar finding is seen in some patients with liver disease. |
| Myeloma | Some paraproteins can interfere with fibrin polymerisation and lead to a prolonged Thrombin and Reptilase time. |
Reference Ranges
The reference range for the Reptilase time is similar to the Thrombin time and is generally in the range of 13-15s.
What Test Next
The following table summarises the abnormalities of the Thrombin time and Reptilase time. This can guide the most appropriate investigation.
Thrombin Time |
Reptilase Time |
|
|---|---|---|
| Presence of unfractionated heparin | ↑ | Normal |
| Presence of LMWH | May show some prolongation | Normal |
| Presence of direct Thrombin inhibitors | ↑ | Normal |
| Warfarin | Normal | Normal |
| Decreased/absent Fibrinogen | ↑ | ↑ |
| Dysfibrinogenaemia | ↑ | ↑ |
| DIC | ↑ | ↑ |
| Liver disease | ↑ | ↑ |
| Heparin-like anticoagulants | ↑ | Normal |
| Paraproteinaemias | ↑ | ↑ |
| Thrombolytic therapy | ↑ | ↑ |
| Neonate | ↑ | ↑ |
| Amyloid | ↑ | ↑ |
| Hyperfibrinogenaemia | ↑ | ↑ |
| Hypoalbuminaemia | ↑ | ↑ |