Abstract
Lupus anticoagulant (LA) is one of the three criteria antiphospholipid antibodies
(aPLs) employed in classification, and by default diagnosis, of antiphospholipid syndrome
(APS). Detection of LA is not via calibrated assays but is based on functional behavior
of the antibodies in a medley of coagulation assays. A prolonged clotting time in
a screening test is followed by demonstration of phospholipid dependence and inhibitory
properties in confirmatory and mixing tests, respectively, which are modifications
of the parent screening test. Complications arise because no single screening test
is sensitive to every LA, and no test is specific for LA, because they are prone to
interference by other causes of elevated clotting times. Several screening tests are
available but the pairing of dilute Russell's viper venom time (dRVVT) with LA-sensitive
activated partial thromboplastin time (aPTT) is widely used and recommended because
it is proven to have good detection rates. Nonetheless, judicious use of other assays
can improve diagnostic performance, such as dilute prothrombin time to find LA unreactive
with dRVVT and aPTT, and the recently validated Taipan snake venom time with ecarin
time confirmatory test that are unaffected by vitamin K antagonist and direct factor
Xa inhibitor anticoagulation. Expert body guidelines and their updates have improved
harmonization of laboratory practices, although some issues continue to attract debate,
such as the place of mixing tests in the medley hierarchy, and areas of data manipulation
such as assay cut-offs and ratio generation. This article reviews current practices
and challenges in the laboratory detection of LA.
Keywords
activated partial thromboplastin time - antiphospholipid syndrome - antiphospholipid
antibodies - dilute prothrombin time - dilute Russell's viper venom time - lupus anticoagulant
- Taipan snake venom time
