Sickle Cell Anemia

Sickle cell anemia is suspected based on an individ ual's ethnic or racial background, and on the symptoms of anemia. A blood count reveals the anemia and the presence of sickle cells in blood samples is easily confirmed by microscopic examination. A sickle cell test can reveal the presence of the sickle cell trait.

The sickle cell test involves mixing equal amounts of blood and a 2% solution of sodium bisulfite. Under these circumstances, hemoglobin exists in its deoxygenated state. If hemoglobin S is present, the red blood cells are transformed into the characteristic sickle shape. This transformation is observed with a microscope, and quantified by expressing the number of sickle cells per 1,000 cells as a percentage. The sickle cell test confirms that an individual has the sickle cell trait, but it does not provide a definitive diagnosis for sickle cell anemia.

To confirm a diagnosis of the sickle cell trait or sickle cell anemia, another laboratory test called gel electrophoresis is performed. This test uses an electric field applied across a slab of gel-like material to separate protein molecules based on their size, shape, or electrical charge. Although hemoglobin S (sickle) and hemoglobin A (normal) differ by only one amino acid, they can be clearly separated using gel electrophoresis. If both types of hemoglobin are identified, the individual is a carrier of the sickle cell trait; if only hemoglobin S is present, the person most likely has sickle cell anemia.

The gel electrophoresis test is also used as a screening method for identifying the sickle cell trait in newborns.

More than 40 states screen newborns in order to identify carriers and individuals who have inherited the trait from both parents. Physicians and researchers also recommend that individuals likely to be exposed to low oxygen tensions (e.g. pilots, divers) undergo screening tests for sickle-cell trait, as studies have shown that those with sickle-cell trait are often less able to cope with low oxygen levels than individuals with normal hemoglobin.