Sickle cell disease (SCD) is a group of inherited blood disorders characterized by an abnormal form of hemoglobin, the protein responsible for carrying oxygen in red blood cells. Instead of their typical round shape, red blood cells become rigid and take on a crescent or “sickle” shape under certain conditions. These misshapen cells can block blood flow, leading to anemia, intense pain episodes, and organ damage. Testing serves as a foundational step toward early diagnosis, comprehensive medical care, and improved long-term health outcomes.
The Purpose of Testing
Testing for sickle cell is performed for multiple reasons across an individual’s lifespan, starting with public health screening for newborns. Newborn screening programs are mandated across the United States to identify the condition within the first days of life. Early detection is paramount because infants with SCD are highly susceptible to severe bacterial infections, particularly those caused by Streptococcus pneumoniae. Starting prophylactic care, such as daily oral penicillin, before two months of age significantly reduces the risk of childhood mortality from these infections.
Testing is also performed as a diagnostic tool for children or adults who present with symptoms suggestive of SCD, such as unexplained anemia, jaundice, or episodes of sudden, severe pain. This diagnostic testing confirms whether the symptoms are directly related to the presence of abnormal hemoglobin. A third application is carrier screening, which is offered to individuals or couples for reproductive planning. Knowing one’s carrier status allows parents to understand the risk of passing the gene mutation to a future child.
Types and Procedures of the Test
The specific procedure used for sickle cell testing depends on the age and clinical situation of the individual. For newborns, the process begins with a simple heel prick shortly after birth, where a few drops of blood are collected onto a specialized filter paper card to create a dried blood spot (DBS) sample. This DBS sample is then analyzed in a laboratory using precise methods to separate and identify different types of hemoglobin present.
The most common primary screening techniques are High-Performance Liquid Chromatography (HPLC) and Isoelectric Focusing (IEF). HPLC separates the hemoglobin variants based on their chemical interaction with a column matrix. IEF separates the hemoglobin proteins based on their electrical charge. These methods provide a presumptive result indicating the presence and quantity of abnormal hemoglobin S (HbS).
For older children and adults, a standard venous blood draw is performed, and the sample is analyzed using methods like hemoglobin electrophoresis or genetic testing. If newborn screening results are abnormal, a second venous blood draw is required within the first few months of life to confirm the diagnosis using these more detailed methods.
Prenatal Testing
Prenatal testing, which is performed when parents are known carriers, involves analyzing DNA from the fetus. This is achieved either through Chorionic Villus Sampling (CVS), which collects a small tissue sample from the placenta around 10 to 13 weeks of pregnancy, or Amniocentesis, which collects amniotic fluid around 15 to 24 weeks.
Understanding Test Results
Sickle cell test results are typically reported by identifying the specific types of hemoglobin found in the blood, which correspond to the inherited genes. A normal result, labeled Hemoglobin AA, means the individual inherited two genes for normal adult hemoglobin and neither the sickle cell trait nor the disease is present. An interpretation of Hemoglobin AS indicates the Sickle Cell Trait, meaning the individual inherited one normal gene (A) and one sickle cell gene (S). Individuals with the trait are generally healthy but are carriers who can pass the sickle gene to their children.
A diagnosis of Sickle Cell Disease (SCD) means the individual inherited two abnormal hemoglobin genes, resulting in the condition. The most common form is Hemoglobin SS, where a person inherits two sickle cell genes. Other forms, such as Hemoglobin SC or Hemoglobin S-beta thalassemia, involve inheriting the sickle gene from one parent and a different abnormal hemoglobin gene from the other. These compound forms are also considered SCD, but their clinical severity can vary.
The specific genotype, such as SS or SC, dictates the required long-term medical management and prognosis. Following a positive screening result for SCD, the family is immediately referred to a pediatric hematologist, a doctor specializing in blood disorders. Genetic counseling is also offered to help families understand the inheritance pattern, the specific implications of the diagnosis, and options for future reproductive planning.