No abstract

A study is presented which assesses the diagnostic impact of incorporating Taipan snake venom time (TSVT) with ecarin time confirmatory test into an existing dilute Russell's viper venom time (dRVVT) and activated partial thromboplastin time (APTT) repertoire when testing nonanticoagulated patients for lupus anticoagulants. A total of 387 plasma samples from nonanticoagulated patients being investigated for antiphospholipid antibodies were tested for lupus anticoagulant by dRVVT and dilute APTT with confirmatory and mixing tests, and TSVT with ecarin time, with commercially available reagents. All were analyzed on a Sysmex CS2000i automated analyzer. Lupus anticoagulant was not detected by dRVVT, dilute APTT or TSVT screening in 265 of 387 (68.5%) samples. A lupus anticoagulant was detected in 60 (15.5%) samples in dRVVT and/or dilute APTT analysis, but gave normal TSVT ratios. Thirty-nine (10.1%) were positive by TSVT and ecarin time and one or both of dRVVT and dilute APTT testing, whereas a further 23 (5.9%) were only positive in TSVT/ecarin time testing. Most of the lupus anticoagulants manifested in dRVVT and/or APTT analysis, as might be anticipated for this reagent pairing. The samples positive by TSVT/ecarin time only, as has been previously demonstrated, emphasize that the many variables that impact lupus anticoagulant testing mean that even a well established dRVVT and APTT pairing cannot deliver diagnostic certainty. Interference by direct factor Xa inhibitors in dRVVT testing could pave the way for wider adoption of TSVT screening as we gain more evidence of its diagnostic performance.

Many departments only screen with MAPC-R to detect just FV mutations. Concurrent performance of CAPC-R and MAPC-R increases diagnostic capability by detecting acquired APC-R. Elevated baseline clotting times can invalidate APC-R ratios, although prolongation by LA alone may not.