Additional Information

The package includes both functional lupus anticoagulant (LA) testing and antigenic testing for detection of antiphospholipid antibodies.

The package includes functional LA testing by three independent systems one based on a dilution of the Russell viper venom time (Dilute Russell Viper Venom Time, or DRVVT ), one based on a dilution of the activated partial thromboplastin time (PTT-LA ), and one based on a dilution of the prothrombin time ( dPT ). In each case a screening test is performed. If results in the screen are sufficiently prolonged, testing will proceed to a mixing study. If there is not sufficiently strong correction of the abnormality in the mixing phase, testing will then proceed to a confirmatory phase for that testing system. While the actual number of seconds of clotting times in the various phases of the specific testing systems necessarily varies as a function of reagent lot changes, the criterion for determination of normal vs abnormal with respect to detection of a LA remains constant: A 99th percentile upper limit for the normal reference population is determined for the confirmatory phase in each testing system at the time of lot changes, and is used as the basis for reporting of results in EPIC.

The package also includes testing for the presence of IgG and IgM antibodies directed against beta-2 glycoprotein I (beta-2 GPI). Because the conformational presentation of beta-2 GPI determines whether or not a particular patient antibody will recognize it as an antigenic target, the beta-2 GPI is employed in two different forms. The first employs the beta-2 GPI directly attached to solid phase, and is termed the IgG or IgM anti-beta-2 GPI  assay. The second employs cardiolipin directly attached to the solid phase, with beta-2 GPI then secondarily being bound to the cardiolipin, and is termed the IgG or IgM anti-cardiolipin  assay.

Note: Each of the three functional LA testing systems now in use employ a heparin-neutralizing agent capable of neutralizing levels of heparin employed therapeutically in patients. However, with the advent of direct thrombin inhibitors, these tests will no longer function properly to detect possible LAs. Accordingly, if the aPTT-LA screen is prolonged, a TT will be performed. If this TT is prolonged, then a TT preceded by incubation of the plasma with heparinase will be performed to determine if heparin might be the cause of the prolongation. In contrast to plasma anticoagulated with unfractionated or low molecular weight heparin, plasma anticoagulated with direct thrombin inhibitors will not show a shortening of the TT following heparinase incubation.