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The Taipan snake venom time: a new test for lupus anticoagulant
A M Rooney1, T McNally, I J Mackie
1Department of Haematology, University College London Medical School.
Aims:
To develop a specific test for lupus anticoagulant activity with reduced sensitivity to coagulation factor deficiency that would be suitable for analysis of plasmas from patients receiving oral anticoagulants.
Methods:
A coagulation test based on the Taipan snake venom time (TSVT) with a platelet neutralisation procedure (PNP) was developed and compared with dilute Russell's viper venom time (DRVVT). The TSVT was used to test plasmas from patients receiving oral anticoagulant or heparin with mild liver dysfunction and with documented lupus anticoagulant.
Results:
The optimised conditions for the TSVT were established and a reference range was determined in normal healthy subjects. Results were considered positive for lupus anticoagulant if the ratio was > or = 1.1 and was reduced by > or = 10% or to < 1.1 in the PNP. In 43 samples from patients receiving oral anticoagulants there was no correlation between level of anticoagulation and TSVT, and only seven samples had increased TSVTs. Of these, five corrected on mixing with normal plasma and two gave equivocal results. The patients with mild liver dysfunction all had normal TSVTs. The TSVT in plasmas from patients receiving heparin correlated with the heparin concentrations (as measured by the APTT, r2 = 0.81). Some anticoagulated plasmas showed correction in the PNP and were regarded as false positive. Fourteen of 17 patients known to have lupus anticoagulant (on the basis of DRVVT results) were also positive by the TSVT; two of the remaining three were borderline and one was negative.
Conclusions:
The TSVT showed satisfactory intra-assay precision and reasonable sensitivity to lupus anticoagulant, compared with the DRVVT. The TSVT was influenced by the presence of heparin but was not sensitive to the effects of oral anticoagulant. Like other lupus anticoagulant tests, it does not seem to have a 100% detection rate, but this may be due to the presence of lupus anticoagulant subtypes with distinct activities or the requirement of cofactors other than prothrombin or beta 2 glycoprotein-I.