coagulation screen is more specific than the anticardiolipin antibody elisa in defining a thrombotic subset of lupus patients in 111 lupus patients we compared the potential of the igg and igm anticardiolipin antibody aca enzyme linked immunosorbent assay elisa and four different lupus anticoagulant lac assays partial thromboplastin time ptt of a 11 mixture of patient and control plasma with phospholipids from animal pttst or human brain ptthb ptt with dilutions of human brain phospholipids pl dilution and kaolin clotting time of mixtures of patient and control plasma kct to identify patients with thrombosis 26111 fetal loss 1946 andor thrombocytopenia 11106 the highest specificity for thrombosis 87 was found with ptthb and pl dilution sensitivity 65 detection rate 61 for fetal loss 93 with pl dilution sensitivity 47 detection rate 82 and for thrombocytopenia 83 with kct sensitivity 82 detection rate 36 compared with lac assays the sensitivity of acaelisa was high greater than or equal to 77 but specificity less than or equal to 51 and detection rate less than or equal to 52 were low so a panel of three lac assays ptthb pl dilution and kct can identify lupus patients apparently at risk for thrombosis fetal loss andor thrombocytopenia whereas the acaelisa is insufficiently specific