Sickle cell disease (SCD) is a group of inherited disorders affecting red blood cells, which carry oxygen throughout the body. SCD is caused by a change in the hemoglobin protein, making normally round, flexible cells become stiff and shaped like a crescent moon, or a “sickle.” This abnormal shape obstructs blood flow and leads to serious health complications. Sickle cell trait (SCT) is a related condition where an individual inherits only one copy of the altered gene, making them a carrier. Testing is performed for early detection in infants and for family planning purposes.
Context for Sickle Cell Testing
Testing for sickle cell conditions is integrated into healthcare across several life stages. Universal newborn screening is the most common form of testing in the United States, mandated by state law to identify the condition within days of birth. This initial screening involves a heel-stick procedure where a few drops of blood are collected onto a specialized filter paper card. The blood spots are then analyzed by a state public health laboratory for abnormal hemoglobin types.
Diagnostic testing may be performed later in life for individuals presenting with symptoms suggesting SCD, such as unexplained pain or anemia. This testing typically uses a standard blood draw from a vein. The sample is processed using laboratory techniques like High-Performance Liquid Chromatography (HPLC) or hemoglobin electrophoresis to separate and measure the different types of hemoglobin.
Testing for carrier status is often performed as part of pre-conception or prenatal screening. This is relevant for individuals with a family history of the disease or those belonging to high-prevalence ethnic groups. Carrier tests utilize the same detailed blood analysis methods as diagnostic testing to look for the presence of the sickle hemoglobin protein.
Typical Timelines for Test Results
The time to receive sickle cell test results varies significantly based on the test type, facility, and result status. For mandatory newborn screening, initial results are typically available within one to two weeks after the sample is collected and shipped to the state laboratory. This timeline allows for the rapid initiation of treatment, such as prophylactic penicillin, for infants identified with the disease. If the initial screen suggests a positive result, the state program expedites follow-up to ensure a second, confirmatory test is performed quickly.
Results for standard diagnostic or carrier testing on an older child or adult are often faster than newborn screening. If the sample is processed locally by a high-volume hospital or commercial laboratory, results from hemoglobin electrophoresis or HPLC may be returned within 24 hours to three business days. The speed depends on the lab’s workload and whether the test is run in batches.
The process can take longer if the initial test reveals an abnormal or unclear result, necessitating specialized or confirmatory testing. If the sample needs to be sent to a reference laboratory specializing in rare hemoglobin variants, the waiting period can extend to a week or more. In cases where genetic sequencing is required to definitively identify a complex or rare mutation, the process can take several weeks from the initial blood draw.
Understanding the Meaning of Results
Sickle cell test results are interpreted by identifying the specific hemoglobin types found in the red blood cells, determined by inherited genes. The most common normal result is the genotype AA, meaning the individual has two normal hemoglobin A genes. This finding indicates the person produces only healthy, round red blood cells and does not have the trait or the disease.
A result of AS signifies Sickle Cell Trait, meaning the individual inherited one normal hemoglobin A gene and one abnormal hemoglobin S gene. People with this trait are generally asymptomatic, but they carry genetic information that can be passed to their children.
The diagnosis of Sickle Cell Disease is confirmed when the test identifies two abnormal hemoglobin genes, such as SS, SC, or S-beta thalassemia. An SS result means the individual inherited the sickle hemoglobin S gene from both parents, leading to the most common and often most severe form of the disease. Other combinations, like SC, involve inheriting the S gene and another abnormal hemoglobin gene, resulting in different types of sickle cell disease.