Blood type, often considered as permanent as eye color, is primarily determined by genes inherited from parents. While it remains constant for most people, a person’s blood type can indeed change in specific, rare medical circumstances. Understanding these potential changes is important for medical care.
The Basics of Blood Type Determination
Blood is classified into different types based on the presence or absence of specific protein molecules called antigens on the surface of red blood cells. The two most recognized and medically significant classification systems are the ABO system and the Rh system. The ABO system categorizes blood into four main types: A, B, AB, and O, defined by the presence of A antigens, B antigens, both, or neither.
The Rh system classifies blood as Rh-positive (RhD antigen present) or Rh-negative (RhD antigen absent). Combining these two systems results in eight common blood types, such as A-positive or O-negative. These antigens are inherited from parents, with the combination of inherited alleles dictating an individual’s blood type from birth.
Situations Leading to Apparent Blood Type Changes
While blood type is genetically determined, certain medical conditions can cause it to appear to change without altering the underlying genetic makeup.
Rarely, bacterial infections can temporarily alter blood group antigens. This “acquired B phenomenon” primarily affects individuals with type A blood, where bacterial enzymes modify the A antigen to resemble a B antigen, leading to temporary misidentification as type B blood. This typically occurs in patients with conditions like colon cancer, bowel obstruction, or sepsis, and the apparent change resolves once the infection is treated.
Large blood transfusions can also temporarily alter a person’s blood type. If a patient receives a significant volume of blood from a donor with a different type, their circulating blood may temporarily reflect the donor’s type. For example, an AB patient receiving O-type blood might temporarily test as O. This is not a permanent change, as the recipient’s bone marrow eventually replaces the transfused blood with their original blood type over a few months.
True Blood Type Changes Through Medical Intervention
A person’s blood type can permanently change through hematopoietic stem cell transplantation, commonly known as a bone marrow transplant. This procedure replaces a patient’s diseased bone marrow with healthy stem cells from a donor. Bone marrow is the primary site for producing all blood cells, including red blood cells.
If the recipient and donor have different blood types, the recipient’s blood-producing system gradually shifts to match the donor’s. This occurs as transplanted donor stem cells engraft and begin producing new red blood cells with the donor’s antigens. The conversion can take several weeks to months as the recipient’s original blood cells are replaced. For instance, an A-positive recipient receiving a transplant from an O-type donor will eventually become O-type. This change is an expected outcome, especially since HLA (tissue type) matching is prioritized over ABO blood type in donor selection.
Medical Implications of Blood Type Alterations
Understanding these blood type alterations is important for ongoing medical care, particularly for patients who have undergone hematopoietic stem cell transplantation. Medical professionals must be aware of the recipient’s changing blood type to ensure compatibility for subsequent blood transfusions. After transplant, transfusions are typically provided based on the donor’s blood type once conversion is confirmed. This adjustment is essential for preventing adverse reactions and ensuring patient safety. Accurate and updated medical records reflecting the new blood type are also important for any future medical procedures or emergencies, ensuring continuity of care.