Scanning electron microscopy of RBCs from a high S-Oman patient. (A) Oxygenated; (B) deoxygenated. Notice the yarn/knitting needle shape of the irreversibly sickled cells characteristic of this disease, highlighted by white arrows. Notice that after full deoxygenation almost all of the cells sickled with long, thin protuberances. The lower two panels (C) and (D) are of a low S-Oman patient. (C) Oxygenated, looks quite normal except for a few echinocytic and otherwise deformed RBCs. No yarn/knitting needle cells. (D) Fully deoxygenated cells; again, almost all of the cells sickle, but with less elongated and numerous protuberances.