The effects of aPL plasmas on annexin-V bound to aPTT reagent-phospholipid and plasma coagulation with this reagent. (A) aPTT reagent-phospholipid was exposed to four different aPL and control plasmas and then to annexin-V (2 μg/mL), after which surface annexin-V was dissociated with EDTA and measured by ELISA. aPTT reagent-phospholipid, which had been preexposed to aPL-plasmas, had significantly less annexin-V (mean ± SEM, 318 ± 28 ng/50 μL aliquot of reagent) as compared with controls (656 ± 80 ng/50 μL aliquot of reagent, P = .01). (B) Plasma coagulation times were determined using aPTT reagent-phospholipid exposed to the aPL and control plasmas (n = 10 for each group) in the first stage and then in the second stage, to pooled normal plasma in the presence and absence of added annexin-V (30 μg/mL). Annexin-V delayed the coagulation times of aPTT reagent exposed to both types of plasmas. In the presence of annexin-V, the coagulation times of the aPTT reagent, which had been preexposed to aPL-plasma, was significantly faster (mean ± SEM, 89.2 ± 2.2 seconds) than reagent exposed to the control plasma (102.5 ± 2.6 seconds, P = .001). Also, there was a significant decrease in the net prolongation of the coagulation times induced by annexin-V (mean ± SEM, 13.6 ± 1.8 seconds for aPL plasmas versus 23.1 ± 0.8 seconds for controls, P = .0002).