INCREASED ERYTHROCYTE PHOSPHATIDYLSERINE EXPOSURE IN SICKLE-CELL DISEASE - FLOW-CYTOMETRIC MEASUREMENT AND CLINICAL ASSOCIATIONS

Increased exposure of phosphatidylserine (PS) in erythrocytes has been postulated to contribute to the pathophysiology of sickle cell diseas e because of its possible effects on blood coagulation, cell adhesion, and cell clearance, We developed a flow-cytometric assay to measure e xposure of PS on the outer face of the erythrocyte membrane based on a ddition of fluorescein-annexin V to whole-blood specimens. The assay c orrelated linearly with binding of I-125-annexin V (r(2) = .95, n = 12 5 samples). Normal donors (n = 30) showed virtually no annexin-positiv e cells (0.34% +/- 0.18% for 24-hour old samples). In contrast, annexi n V binding was above the upper limit of normal in 96% of 205 specimen s from 17 adult sickle cell and 2 beta-thalassemia patients; the mean percentage of annexin-positive cells was 2.86% +/- 2.00% (range, 0.4% to 12.0%). Values varied substantially over time for some patients, an d mean values varied between patients, The percentage of annexin-posit ive cells always decreased after transfusion (11 events in 6 patients) , and out of proportion to the amount of blood transfused. In conclusi on, increased exposure of PS on a subpopulation of erythrocytes in viv o is a virtually universal feature of sickle cell disease, and its mea surement may be useful to evaluate clinical status and response to the rapeutic measures such as blood transfusion. (C) 1996 by The American Society of Hematology.