Sickle cell disease is an inherited blood disorder that is defined by the presence of hemoglobin S which occurs in either the homozygous (SS-sickle cell anemia) or heterozygous (AS-sickle cell trait) forms. The disease is characterized by chronic anemia, painful events and various complications associated with tissue and organ damage. The most common and well-known type of sickle cell disease is sickle cell anemia, also called SS disease which can be fatal prior to adolescence if not diagnosed. All types of sickle cell diseases are caused by a genetic change in hemoglobin--the oxygen-carrying protein inside the red blood cells. The red blood cells of affected individuals contain a predominance of a structural variant of the usual adult hemoglobin (A). This variant hemoglobin, called sickle hemoglobin, has a tendency to polymerize into rod-like structures that alter the shape of red blood cells. The cells have a sickle shape and a shorter life span (10 to 20 days) than normally shaped red blood cells (120 days). This results in chronic anemia characterized by low levels of hemoglobin and decreased numbers of red blood cells. Sickle cells are also less flexible and more sticky than normal red blood cells and can become trapped in small blood vessels preventing blood flow. This compromises the delivery of oxygen which can result in pain and damage to associated tissues and organs. Carriers of the sickle cell gene are said to have sickle cell trait (AS). Unlike sickle cell disease, sickle cell trait does not cause health problems. However, persons with sickle cell trait can pass the gene to their children. Therefore, it is extremely important to test for hemoglobin SS (sickle cell disease) and AS (sickle cell trait) in high risk individuals so that these individuals can be identified and the resultant consequences of the disease reduced.
The prevalence of sickle cell disease (SS) in the United States is 0.2% among African Americans and 0.1% among Hispanic Americans. The prevalence of sickle cell trait (AS) is 10% among African Americans. Internationally the disease is most frequently found in sub-Saharan Africa. However, it is also found in regions of Sicily, Greece, southern Turkey, and India. Early diagnosis of sickle cell anemia is very important so that children who have the disease can receive proper treatment. Forty-four (44) States, the District of Columbia, Puerto Rico, and the Virgin Islands currently screen all newborns for sickle cell anemia. Screening is available by request in the other six (6) States. This screening includes a simple blood test for sickle cell anemia on all newborn infants and uses blood from the same blood samples as other routine newborn screening tests. If the first test shows that the sickle hemoglobin is present, a second blood test is done to confirm the diagnosis. These tests also tell whether the child carries the sickle cell trait.
The Chembio Sickle-STAT assay is a qualitative screening test for the detection of hemoglobin S in blood samples. The test is used in conjunction with other criteria for the diagnosis of sickle cell disease.
