Blood donation provides life-saving support for patients facing trauma, surgery, chronic disease, and blood disorders. Given the constant need for a diverse and robust blood supply, questions about donor eligibility are common, especially concerning genetic conditions. One such question frequently arises from individuals who carry the Sickle Cell Trait (SCT), a genetic variation that affects red blood cells. The presence of this trait introduces specific considerations for blood collection organizations regarding the safety and usability of the donated blood product for all recipients.
What is Sickle Cell Trait (SCT)?
Sickle Cell Trait is a genetic condition resulting from inheriting one gene for normal hemoglobin (HbA) and one gene for sickle hemoglobin (HbS). This genetic makeup is denoted as HbAS, making the individual a carrier of the trait. SCT is distinct from Sickle Cell Disease (SCD), which occurs when two HbS genes are inherited, causing severe illness. Individuals with SCT are generally healthy and do not experience symptoms under normal physiological conditions. However, the presence of the HbS gene influences a person’s eligibility to donate certain blood components.
Blood Donation Eligibility Rules for SCT Carriers
Individuals with Sickle Cell Trait are generally eligible to donate blood, but their donation may be restricted to specific components. Major blood collection organizations, like the American Red Cross, permit SCT carriers to donate plasma and platelets. This is because the medical concern primarily involves the red blood cell component. SCT carriers are typically restricted from donating whole blood or Power Red (double red cell) donations. This limitation is not due to a concern for the donor’s health, as donating blood does not pose additional risk to individuals with SCT, but rather a quality control measure applied during processing.
The Biological Rationale for SCT Restrictions
The primary restriction on using red blood cells from SCT carriers stems from the unique behavior of the sickle hemoglobin under certain conditions. While SCT red cells function normally in the donor’s body, they become vulnerable to sickling when exposed to low oxygen levels (hypoxia). This low oxygen tension can occur during the standard blood storage process in a blood bank. When oxygen saturation drops, the HbS within the red blood cells can polymerize, causing the cells to become stiff and misshapen. This sickling process presents a significant problem during a required step in blood processing called leukocyte reduction (leukoreduction).
Leukoreduction involves filtering the donated blood to remove white blood cells, a step performed on nearly all transfusable red cell units. The stiff, sickled red cells from SCT carriers can clog and occlude the fine filters used for leukoreduction, causing the filtration process to fail. This prevents the unit from being processed into a usable red cell product. Furthermore, a second biological concern relates to the recipient, particularly vulnerable patients who may be exposed to low oxygen levels, such as neonates or patients undergoing exchange transfusions. Transfusing SCT red cells into these patients carries a higher risk, as the sickled cells could impede blood flow and cause harm.
How Blood Centers Handle SCT Donations
Blood centers perform routine screening for the presence of hemoglobin S on donations from self-identified multiracial and Black or African American donors, as the trait is most prevalent in these populations. This screening is often done using a molecular test, which provides accurate identification of the trait status. Once a unit is identified as SCT-positive, the blood center determines how the components can be safely utilized. The red blood cells are typically barred from use in high-risk situations, such as transfusions for newborns or patients with Sickle Cell Disease. However, components like plasma and platelets, which do not rely on the integrity of the red blood cells, are generally acceptable and fully utilized.