Sickle cell anemia is a severe hemolytic anemia resulting from the inheritance of the sickle hemoglobin (HbS) gene, which causes a defective hemoglobin molecule.
The defective hemoglobin molecule assumes a sickle shape when exposed to low oxygen tension. These long, rigid RBCs become lodged in small vessels and can obstruct blood ﬂow to body tissue. If ischemia or infarction results, the patient may have pain, swelling, and fever. The sickling process takes time; if the erythrocyte is again exposed to adequate amounts of oxygen (eg, when it travels through the pulmonary circulation) before the membrane becomes too rigid, it can revert to a normal shape. For this reason, the “sickling crises” are intermittent.
The HbS gene is inherited, with some people having the sickle cell trait (a carrier, inheriting one abnormal gene) and some having sickle cell disease (inheriting two abnormal genes). Sickle cell disease is found predominantly in people of African descent and less often in people who have descended from the Mediterranean countries, the Middle East, or aboriginal tribes of India.