Flow cytometric analyses of PS-positive erythrocytes in whole blood from a representative patient with SCD.

Dot plots of forward size scatter verses anti-CD235a–PE fluorescence from a blood sample stained in the presence of EDTA and calcium are presented in panels A and B, respectively. Region R1 in these dot plots represents red cell–associated events. Histogram profiles of annexin V–FITC fluorescence of erythrocytes stained in the presence of EDTA and calcium are presented in panels C and D, respectively. Annexin V–negative (gate M1) and –positive (gate M2) histogram regions were set by using the blood sample stained in the presence of EDTA as shown in panel C. The histogram profile presented in panel D demonstrates the presence of a distinct subpopulation of PS-positive erythrocytes (gate M2).