The effects of aPL plasmas on the binding of FITC–annexin-V to aPTT reagent-phospholipid. aPTT reagent was incubated with aPL and control plasmas (n = 10 for each group), after which 1 μg/mL of FITC–annexin-V was added. Annexin-V bound to the aPTT reagent and in the fluid phase were quantified by spectrofluorimetry, as decribed in Materials and Methods. There was a significant decrease of the amount of annexin-V associated with the aPTT reagent, which had been preincubated with aPL plasmas (mean ± SEM, 0.083 ± 0.008 RFU/50 μL aliquot of reagent) compared with controls plasmas (0.131 ± 0.015 RFU/50 μL aliquot of reagent,P = .01). In contrast, there was a significant increase in the amount of labeled annexin-V remaining in the supernatant of aPTT reagent, which had been preincubated with aPL plasmas (mean ± SEM, 0.070 ± 0.008 RFU/50 μL aliquot of reagent) as compared with control plasmas (0.046 ± 0.005 RFU/50 μL aliquot of reagent,P = .02).