Interpretation

The diagnosis of a lupus anticoagulant (LA) requires performance and interpretation of complex coagulation testing, as well as correlation with available clinical information. Because of the heterogeneous nature of LA antibodies, no single coagulation test can identify or exclude all LAs. Consequently, a combination or panel of coagulation tests are performed, including the activated partial thromboplastin time (aPTT) and the dilute Russell's viper venom time (dRVVT). If the aPTT or dRVVT is prolonged, additional testing may include mixing tests with normal plasma (to demonstrate inhibition) and the use of excess phospholipid in appropriate assay systems to confirm the presence of LA.

Interpretation of hexagonal LA testing is complex and must be done within the context of several additional laboratory tests (eg, aPTT with reflexive aPTT mixing study and platelet neutralization procedure [PNP]; and dRVVT with reflexive mixing study and confirmatory procedure). Hexagonal LA is effective in evaluating a prolonged aPTT resulting from inhibition. The assay involves the addition of a reaction mixture with and without hexagonal phase phospholipid to the patient's platelet-poor plasma. A silica-based aPTT is done on both mixtures and the clotting times are compared. Plasma containing a LA will demonstrate significant shortening of the aPTT with addition of hexagonal phase phospholipid (by at least 13 seconds), when compared to aPTT without hexagonal phase phospholipid. Additional phospholipid supplied by the hexagonal phase phospholipid reagent can absorb LA antibody (anti-protein/phospholipid), thereby diagnostically shortening the aPTT. A hexagonal LA delta of less than 13 indicates LA negative and greater or equal to 13 seconds is LA positive for this assay.

Per manufacturer studies hexagonal LA compared to Staclot LA data demonstrated positive percent agreement of 95.6% (95% CI, 91-98%), negative percent agreement of 95.2% (95% CI, 92%-97%), and overall agreement of 95.3% (95% CI, 93%-97%).