Method Description

Hexagonal lupus anticoagulant (Hex LA) is an integrated (screen and confirmation) silica-based activated partial thromboplastin time (aPTT) assay for qualitative LA detection performed on the Instrumentation Laboratory ACL TOP instrument. The procedure is based on the following principle: the test plasma that is suspected to contain a LA is incubated either with hexagonal phase phospholipid (tube 2) or without (tube 1). A pooled normal plasma (mixing test) and a heparin neutralizer are present in both tubes to correct for any prolongation of the clotting time due to factor deficiencies that may be present. Next, an aPTT is performed on both tubes using a LA-sensitive partial thromboplastin reagent. If LA is present in the test plasma, the LA would typically be neutralized by the hexagonal phase phospholipid in tube 2 but not by the buffer in tube 1, resulting in shortening of the clotting time (by 13 seconds or greater) of tube 2 compared with that of tube 1. By comparing the difference between the 2 clotting times, the presence of LA antibodies (anti-protein/phospholipid) in the test plasma can be identified.(Triplett DA, Barna LK, Unger GA. A hexagonal II phase phospholipid neutralization assay for lupus anticoagulant identification. Thromb Haemost. 1993;70[5];787-793; Clinical Laboratory Standards Institute (CLSI). Laboratory Testing for the Lupus Anticoagulant; Approved Guideline. CLSI H60-A. CLSI; 2014; package insert: Hex LA Kit, Precision Biologic; Rev. 04, Dec 2020)

The incorporation of a heparin neutralizer in the Hex LA assay system allows testing when heparin is in the sample. Accurate results can be expected in samples containing up to 2 IU/mL of heparin. The Hex LA method also includes the addition of normal plasma to correct for coagulation factor deficiencies that may result in a prolonged aPTT. This enables testing of specimens from patients receiving oral anticoagulant therapy, as well as those with other congenital or acquired coagulation factor deficiencies, as a cause of the prolonged aPTT.