Annexin A5 resistance assays for patient plasma groups. The annexin A5 anticoagulant ratio for the aPL syndrome with thromboembolism group (A) was significantly decreased (mean ± SD, 182 ± 31%, n = 25) compared with the aPL antibodies without thrombosis history group (B) (210 ± 35% [n = 26], P < .01), the non-aPL thromboembolism group (C) (229 ± 16% [n = 15], P < .001), and the healthy control group (D) (231 ± 14% [n = 30], P < .001). The ratio for the plasmas from the aPL antibodies without thrombosis history group (B) also was significantly reduced compared with the healthy control group (D) (P < .05). There were no significant differences in annexin A5 anticoagulant ratio for the non-aPL thromboembolism group (C) compared with the aPL antibodies without thrombosis history group (B) and the healthy control group (D). Error bars are shown for mean ± 2 SD of normal healthy controls (D).