AN APPROACH TO FACTOR ASSAYS IN PATIENTS WITH STRONG LUPUS ANTICOAGULANTS

High-titer lupus anticoagulants (LACs) may present technical and diagn ostic difficulties in the evaluation of patients with specific factor deficiencies or inhibitors. These potent LACs, although infrequently e ncountered, may be very confusing because they do not generate the cha racteristic pattern of rising factor levels with increasing sample dil utions. In addition, they may prevent assessment of individual factor defects by lowering activities below detectable or evaluable levels (< 1%). To help resolve these problems, our laboratory has developed an a pproach that incorporates a variation of the platelet neutralization p rocedure (PNP), wherein we add phospholipid (PL) to adsorb the LAC in each of the dilutions of the individual factor assays. Using factor VI II for the prototypic studies, we characterized three basic result pat terns that might arise, depending on the amount of factor activity rec overed. As observed in patients exhibiting two of these patterns, an a ppreciable increase in activity agrees with the neutralization of a LA C and provides evidence against a coexistent severe deficiency of that factor and presumptive evidence against a coexistent, strong specific factor inhibitor.