LABORATORY IDENTIFICATION OF LUPUS ANTICOAGULANTS - RESULTS OF THE 2ND INTERNATIONAL WORKSHOP FOR IDENTIFICATION OF LUPUS ANTICOAGULANTS - ON BEHALF OF THE SUBCOMMITTEE ON LUPUS ANTICOAGULANTS ANTIPHOSPHOLIPIDANTIBODIES OF THE ISTH

Lupus anticoagulants (LAs) are antibodies that interfere with phosphol ipid dependent coagulation reactions in vitro. This workshop was desig ned to provide the participants with an experience in identification o f LAs, to evaluate different criteria for mixing studies, to assess th e performance of recently introduced confirmatory studies and to asses s the performance of two potential surrogate LA control plasmas. The r esults demonstrate that there continues to be significant variation in the sensitivity and responsiveness of APTT reagents to the presence o f LAs, confirming the need for more than one screening assay before th e presence of a LA can be ruled out. In this workshop, the best distin ction between factor deficiency and inhibitors was obtained using a I: 1 mix of normal plasma with patient plasma and the criterion defining correction as shortening of the APTT to within 5 s of the APTT of pool ed normal plasma. A 4:1 mix of patient to normal plasma did not work w ell in distinguishing factor deficiency from inhibitors. The platelet neutralization procedure, DVV confirm(R) and StaClot LA(R) all gave po sitive results with the LA samples. False positive platelet neutraliza tion procedures were seen with the samples from patients on oral antic oagulants and a factor V inhibitor. False positive StaClot LA results were obtained with high titer factor VIII inhibitors. Both of the pote ntial surrogate plasmas gave variable results with multiple assays; th ey can not be recommended for routine use at present.