An Approach to Factor Assays in Patients with Strong Lupus Anticoagulants

Higb-titer lupus anticoqgulants (LACs) may present technical and diagnostic dffficulties in the evaluation of patients with specific factor deficiencies or inhibitors. These potent LACS, although infrequently encountered, may be very confusing because they do not generate the characteristic pattern of rising factor levels with increasing sample dilutions. 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 taboratory has developed an approach that incorporates a variation of the platelet neutralization procedure (PNP), wherein we add phospholipid (PL) to adsorb the LAC in each of the dilutions of the individual factor assays. Using factor VIII for the prototypic studies, we characterized three basic result patterns that might arise, depending on the amount of factor activity recovered. As observed in patients exhibiting two of these patterns, an appreciable increase in activity agrees with the neutralization of a LAC and provides evidence against a coexistent severe deficiency of that factor and presumptive evidence against a coexistent, strong specific factor inhibitor.