The sickle cell test is a blood analysis designed to identify abnormal types of hemoglobin, the protein in red blood cells that transports oxygen throughout the body. Abnormal hemoglobin variants cause sickle cell conditions, which can range from being a carrier to having a serious disease. Understanding the results involves recognizing a combination of letters that represent the specific types of hemoglobin found in the blood sample. This information helps determine a person’s genetic status, whether they have the trait or the disease, and informs necessary follow-up care.
Context of Sickle Cell Testing
The need for a sickle cell test arises in several distinct circumstances across a person’s lifespan. Universal newborn screening is the most common time the test is performed, allowing for the early detection of sickle cell disease to begin timely treatment and care. This initial screen uses a blood sample, often collected through a heel stick, to check for abnormal hemoglobin proteins.
Testing is also administered for diagnostic purposes when an individual shows symptoms that align with a sickle cell condition, such as unexplained anemia or episodes of severe pain. Additionally, carrier screening is offered to adults planning a family to determine if they carry a gene for an abnormal hemoglobin variant. Knowing one’s carrier status is important for understanding the genetic risk of passing on a sickle cell disease to a child.
Decoding the Hemoglobin Letter Notation
A sickle cell test result report uses letters to represent the different types of hemoglobin detected in the blood. The letter “A” signifies normal adult hemoglobin, which is the type most people have in the highest concentration. The presence of two “A” genes indicates a person has entirely normal hemoglobin and does not have a sickle cell condition.
The letter “S” stands for sickle hemoglobin, the abnormal variant responsible for the characteristic sickle shape of red blood cells under low-oxygen conditions. Other letters represent different abnormal hemoglobin types that can interact with the S gene to cause disease. For example, “C” represents Hemoglobin C, another abnormal variant that is generally less severe than Hemoglobin S.
The test may also detect other variants like “E” or components indicating beta-thalassemia, which are genetic conditions that affect the production of hemoglobin chains.
Interpreting the Possible Result Combinations
The result is typically reported as a two-letter combination, representing the two hemoglobin genes an individual inherited, one from each parent.
AA: Normal Hemoglobin
The most common result is “AA,” which indicates that a person has two normal hemoglobin genes. This outcome means the person produces only normal adult hemoglobin and does not have sickle cell disease or the trait.
AS: Sickle Cell Trait (SCT)
A result of “AS” signifies the presence of both normal hemoglobin (A) and sickle hemoglobin (S). Individuals with SCT are carriers, meaning they inherited one normal gene and one sickle gene. They usually do not experience the symptoms of sickle cell disease because they produce enough normal hemoglobin. While SCT is generally benign, it carries a risk of passing the sickle gene to children, and rarely, symptoms may occur under extreme conditions like intense physical exertion or high altitude.
SS: Sickle Cell Disease (SCD)
The result “SS” identifies the most common and often most severe form of the condition, sometimes called sickle cell anemia. This result means the person inherited two sickle hemoglobin genes, leading to the production of almost entirely sickle hemoglobin. This causes chronic anemia and recurring episodes of pain, known as a vaso-occlusive crisis, due to the sticky, crescent-shaped cells blocking blood flow in small vessels.
Other Combinations
Another common result is “SC,” representing Sickle Hemoglobin-C Disease, where a person inherited one sickle gene (S) and one Hemoglobin C gene (C). This is considered a form of sickle cell disease, but it is typically less severe than the “SS” type. Other combinations, such as “S-beta-thalassemia,” involve one sickle gene and one gene for beta-thalassemia, which affects the quantity of normal hemoglobin produced. The severity depends on the specific type of beta-thalassemia gene inherited.
Next Steps After Receiving Results
Receiving a result indicating a carrier status or a form of sickle cell disease requires prompt follow-up. Initial positive screening results, especially in newborns, are considered presumptive and require a second, more definitive diagnostic test, such as hemoglobin electrophoresis or DNA analysis, to confirm the exact diagnosis. This ensures accuracy before initiating any long-term treatment plan.
If the result confirms a diagnosis of sickle cell disease (“SS” or “SC”), the person is immediately referred to a hematologist, a doctor specializing in blood disorders, for comprehensive care. This care often involves starting prophylactic penicillin for infants to prevent serious bacterial infections. For adults or couples who receive a carrier result (AS, AC), genetic counseling is recommended to understand the inheritance patterns and the potential risk to future children.