Identification of the lupus anticoagulant (LA) by laboratory testing is critical for diagnosing the antiphospholipid syndrome and investigating unexpectedly prolonged activated partial thromboplastin time values. The “anticoagulant” effect of LA is restricted to the prolongation of clotting times when using in vitro, clot-based coagulation assays that are used as surrogates for identifying LA. Clinical and Laboratory Standards Institute document H60—Laboratory Testing for the Lupus Anticoagulant; Approved Guideline provides guidance and recommendations regarding the proper collection and handling of the specimen; descriptions and limitations of screening and confirmatory assays, and mixing tests used to identify LA; determination of cutoff values and calculations associated with the various assays; and interpretation of test results in an LA panel. The guideline is provided for use by laboratorians, physician stakeholders, manufacturers of LA assays, researchers, external quality assessment programs, and accrediting and regulatory agencies. The intent of this guideline is to present information in a practical and easily understandable format; thereby facilitating a standardized approach to LA testing, gaining acceptance in practice, and improving testing quality.

This document provides guidance for the performance and interpretation of screening assays, confirmatory assays, and mixing tests used to identify the lupus anticoagulant (LA). It is intended to assist in standardization of LA testing and it addresses preexamination issues, examination concerns, and postexamination matters that pertain to interpretation of individual tests or combinations of assays. Recommendations from this guideline, when feasible, harmonize with other national and international guidelines currently in existence. Taken together, standardization and harmonization will permit laboratories to improve the quality and interpretation of their LA testing. 

The intended users of this guideline are laboratory personnel responsible for performing LA testing, physicians (eg, hematologists, pathologists, rheumatologists), external quality assessment (EQA) programs, researchers, and manufacturers of reagents used in LA testing. 

Two types of methodologies are used for the diagnosis of the antiphospholipid syndrome (APS). This guideline is limited to clot-based coagulation assays used as surrogates for identifying LA—a strong risk factor for thrombosis. The guideline will not address solid-phase testing for anti-phospholipid (aPL) (eg, anti-cardiolipin [aCL] or anti-ß2 glycoprotein I [aß2GPI]), because detection of these specific antibodies may or may not relate to the laboratory anomaly of a prolonged activated partial thromboplastin time (APTT).