Dense red blood cell and oxygen desaturation in sickle-cell disease

Production of abnormal hemoglobin (HbS) in sickle-cell disease (SCD) results in its polymerization in deoxygenated conditions and in sickled-RBC formation. Dense RBCs (DRBCs), defined as density >1.11 and characterized by increased rigidity are absent in normal AA subjects, but present at percentages that vary of a patient to another remaining stable throughout adulthood for each patient. Polymerized HbS has reduced affinity for oxygen, demonstrated by the rightward shift of the oxygen-dissociation curve, leading to disturbances in oxygen transport. Ninety-two SCD patients' total RBCs were separated into LightDRBC (LRBC) (d < 1.11 g/mL) and DRBC fractions. Venous blood partial oxygen pressure and RBC-fraction-deoxygenation and -reoxygenation Hb-oxygen-equilibrium curves were determined. All patients took a 6-minute walking test (6MWT); 10 had results before and after >6 months on hydroxyurea. 6MWT time with SpO(2) < 88% (TSpO(2) < 88) assessed the physiological impact of exertion. Elevated mean corpuscular hemoglobin (Hb) concentrations, decreased % HbF, and 2,3-bisphosphoglycerates in DRBCs modulated Hb-oxygen affinity. Deoxygenation and reoxygenation Hb-oxygen equilibrium curves differed between normal Hb AA and SS RBCs and between LRBCs and DRBCs, with rightward shifts confirming HbS-polymerization's role in affinity loss. In bivariate analyses, 50% Hb saturation correlated positively with % DRBCs (P < 0.0001, r(2) = 0.34) and negatively with % HbF (P < 0.0001, r(2) = 0.25). The higher the % DRBCs, the longer the TSpO(2)88 (P = 0.04). Hydroxyurea was associated with significantly shorter TSpO(2) < 88 (P = 0.01). We report that the %DRBCs directly affects SCD patients' SpO(2) during exertion; hydroxyurea improves oxygen affinity and lowers the % DRBCs. (C) 2016 Wiley Periodicals, Inc.