Peripheral smear and FACS analysis results. (A) Wright-stained peripheral smear (original magnification ×100) from the patient with occasional sickle cells (arrows). (B) Results of FACS analysis for Hb A and Hb S in peripheral erythrocytes from the patient and controls with Hb AA, Hb SS, and Hb AS. The propositus' chimerism of 69% AS cells and 31% SS cells is consistent with the 43.2% Hb A and 52.1% Hb S found through hemoglobin HPLC. The small fraction of peripheral blood cells that remain unstained by antibodies to either Hb A or Hb S probably represents nonerythroid cells or erythrocytes that were insufficiently permeabilized to antibody.