Instalab ResearchBlood type is defined by the presence of antigens on the surface of red blood cells. These antigens are specific carbohydrate structures produced by enzymes that attach sugars to proteins or lipids. The most familiar system is ABO:
Alongside ABO is the Rh system, most notably the D antigen, which classifies blood as positive or negative. These markers are genetic traits, passed from parents to children, and encoded by genes for enzymes called glycosyltransferases. Because they are genetic, blood types are usually lifelong. But clinical medicine tells us there are exceptions.
#1: Bone Marrow and Stem Cell Transplants: One of the most well-documented cases occurs in patients undergoing bone marrow or hematopoietic stem cell transplants. The bone marrow is the blood factory, producing red cells. When it is replaced with a donor’s marrow, the recipient begins producing blood cells of the donor’s type. Over time, the patient’s circulating blood type appears to change from their original to the donor’s.
This does not rewrite the recipient’s DNA, but it does fundamentally change their blood production, making this the clearest real-world example of blood type “changing.”
#2: Weak or Persistent Antigens: Even outside transplantation, antigen expression is more nuanced than most people realize. The Rh system, for example, includes dozens of weak and partial D variants. A person with one of these variants may be typed differently depending on the test method used.
Similarly, after ABO-incompatible stem cell transplants, remnants of the recipient’s original antigens can persist in plasma and attach to donor red cells, creating mixed results in laboratory typing. Clinical studies show that this can continue for months or years, complicating transfusion decisions and making it appear that the patient’s blood type is unstable.
#3: Disease and Antigen Alteration: Diseases that affect the bone marrow or immune system can sometimes alter the way blood type antigens are expressed. Leukemia, for example, can reduce antigen expression on red cells, leading to weaker reactions in blood typing assays. Though rare, these clinical scenarios are well-documented and emphasize that the biology of blood type is not entirely rigid.
#4: Laboratory Method Dependence: Finally, some perceived “changes” are simply the result of how blood type is tested. Different laboratories use different reagents, and subtle discrepancies can arise, particularly after transplantation. Clinical trials have shown that the choice of testing technique can yield different apparent results for the same patient.
#5: Scientific Advances in Altering Blood Type: Beyond natural circumstances, scientists are now developing methods to deliberately change blood type at the cellular level. A breakthrough came with the discovery of enzymes in the human gut microbiome that can strip away A and B antigens from red blood cells. This effectively converts type A or B blood into type O, the universal donor type. The technique is not yet routine but has been validated in laboratory research, offering the promise of expanding safe blood supplies worldwide.
Whether inherited, altered by transplant, or modified in a lab, blood type remains a central concern in medicine. Mismatched transfusions can be fatal, as even small antigen differences can trigger severe immune reactions. Transplant success depends on careful matching, and pregnancies involving Rh incompatibility require preventive treatment to avoid complications for the fetus.
Clinical missteps underline this importance. A single transplant error involving incompatible blood type can have devastating consequences, as documented in widely reported cases.
Knowing your blood type is not just trivia. It is part of your medical identity, essential for safe care in emergencies, surgeries, and childbirth.
Inherited genetics say no. But medicine shows us that yes, in specific circumstances, the blood you carry can shift type. Bone marrow transplants, weak antigens, disease, and advanced biotechnology all demonstrate that blood typing is more dynamic than most people realize.
