F cells and sickle cell anemia

The distribution of concentrations of HbF/F cell might be the critical determinant for some of the complications of sickle cell anemia. In the figure, some F cells, depicted in bright red and orange, have sufficiently high HbF concentration so that under physiologic O₂ saturations their HbS will contain little or no polymer. In the dark and light blue F cells with lesser amounts of HbF, HbS polymerization will occur at venous O₂ saturations. Some of the F cells and other sickle erythrocytes with little or no HbF will hemolyze intravascularly and by releasing their hemoglobin and arginase into the blood, can deplete bioavailable nitric oxide, leading to a number of vascular complications shown here.