Under normal circumstances, your Rh blood type is permanent. If you are Rh-positive, you will stay Rh-positive for life, and the same goes for Rh-negative. The Rh factor is determined by genes you inherit from your parents, and those genes do not spontaneously rewrite themselves. That said, there are genuine medical scenarios in which a person’s blood type, including the Rh factor, does change or appears to change, and the distinction between a true biological shift and a testing artifact matters more than most people realize.
Why Rh Status Is Normally Permanent
Your red blood cells either carry the D antigen on their surface or they do not. If the D antigen is present, you are classified as Rh-positive; if it is absent, Rh-negative. This is controlled by whether you have a functional copy of a gene called RHD. People who are Rh-negative typically have a complete deletion of that gene on both copies of their chromosome. A study examining Rh-negative individuals in a Saudi population found that none of the 66 Rh-negative samples showed any of the key gene segments tested, confirming they were homozygous for the full gene deletion.1PubMed Central. Molecular Background of RhD-positive and RhD-negative Phenotypes in a Saudi Population Because your DNA does not change on its own, the vast majority of people who type as Rh-positive at birth will type as Rh-positive decades later.
Among Rh-positive people, though, there is an important subtlety. Not everyone positive for D antigen expresses it at the same strength. In the Saudi study, about a fifth of Rh-positive individuals had two working copies of the RHD gene, while the remaining roughly four-fifths carried just one working copy alongside one deleted copy.1PubMed Central. Molecular Background of RhD-positive and RhD-negative Phenotypes in a Saudi Population Having one copy versus two does not normally make a person type differently on standard tests, but it sets the stage for some of the gray areas discussed below.
Bone Marrow and Stem Cell Transplant
The one well-recognized medical situation in which blood type genuinely changes is a hematopoietic stem cell transplant, commonly called a bone marrow transplant. When a patient receives donor stem cells, those cells take over blood production. If the donor has a different blood type than the recipient, the patient’s blood will gradually convert to the donor’s type. This applies to both the ABO system and the Rh system. A patient who was Rh-positive before transplant can become Rh-negative if the donor is Rh-negative, and vice versa.
One published case describes a patient who originally had blood group B, received a stem cell transplant from a blood group A donor, converted to group A, and then eventually reverted to his original group B years later. That reversion created a serious problem when he later needed a kidney transplant, because he had been matched as group A based on his post-transplant typing.2Europe PMC. Temporal Change in Blood Group after Bone Marrow Transplant: A Case of Successful ABO-Incompatible Deceased Donor Transplant The case illustrates that blood type after stem cell transplant should be rechecked, because the conversion is not always permanent if the recipient’s own bone marrow partially recovers.
The transition does not happen overnight. Research tracking blood group conversion in 21 patients after stem cell transplants found that the timeline varied considerably depending on the type of blood group mismatch between donor and recipient. In cases where the donor’s blood type differed from the recipient’s in certain ways, the red blood cell conversion took an average of roughly two months, while other mismatch patterns resolved faster, in about three to four weeks.3PubMed. Study on serological blood group conversion rule and clinical blood transfusion in allogeneic hematopoietic stem cell transplantation During the transition period, a patient can have a confusing mix of old and new blood types circulating at the same time, which makes blood transfusion decisions tricky for the medical team.
When Cancer Suppresses Blood Group Antigens
Certain blood cancers can cause a person’s blood group antigens to weaken or temporarily disappear, making it look like their blood type has changed. This has been documented most frequently in myeloid malignancies, which are cancers affecting the bone marrow cells responsible for producing red blood cells. Two patients with acute myeloid leukemia were reported to have lost their normal ABO blood group antigens during active disease, only to have those antigens reappear once they went into remission.4PubMed Central. Blood group change in acute myeloid leukemia
This is not a fluke seen in one or two patients. A study looking specifically at this phenomenon found that over half of patients with blood group A, B, or AB who had myeloid malignancies showed decreased expression of their A or B antigens on a portion of their red cells, compared with no such changes in healthy individuals.5PubMed. Loss of red cell A, B, and H antigens is frequent in myeloid malignancies The mechanism involves the cancer disrupting the enzymes that attach sugar molecules to the red cell surface, which are what define ABO blood types. While most published cases involve the ABO system, the principle that malignancy can interfere with antigen expression applies more broadly and underscores why a sudden, unexplained blood type discrepancy in a patient sometimes prompts further investigation for an underlying blood disorder.
The Weak D Gray Zone
For the Rh system specifically, one of the most common reasons a person’s status might seem to flip between positive and negative has nothing to do with disease or transplant. It has to do with a real biological gray area called weak D. Some people have a version of the RHD gene that produces a D antigen, but in much smaller quantities than usual. Whether these individuals type as Rh-positive or Rh-negative can depend entirely on how sensitive the test is.
The medical community has historically handled weak D patients differently depending on the context. Blood donors with a weak D phenotype have typically been treated as Rh-positive, since their red cells could still trigger an immune response in an Rh-negative recipient. But transfusion recipients and pregnant women with weak D have been treated as Rh-negative, to protect them from potential sensitization.6PubMed Central. Serological weak D phenotypes: a review and guidance for interpreting the RhD blood type using the RHD genotype This means the same person could be classified as Rh-positive in one medical record and Rh-negative in another, depending on the clinical scenario and the institution’s policy.
Genetic testing has revealed the diversity underlying weak D. A Korean study identified multiple distinct RHD gene variants among weak D samples, each producing different levels of D antigen on the red cell surface. Some variants produce enough antigen to react in one testing method but not another, which explains why a patient might get discordant results from different labs or different testing platforms.7PubMed Central. Molecular basis of serological weak D phenotypes and RhD typing discrepancies identified in the Korean population In that study, some samples typed as D-positive on an automated system but showed only weak reactivity on a manual method, highlighting how test sensitivity can flip a result. For someone who has been told their blood type at different points in life and gotten different answers, weak D variants are the most likely explanation.
Lab Errors and Autoimmune Interference
Not every apparent blood type change reflects something happening in the body. Sometimes the problem is in the lab. Blood typing relies on mixing a person’s red cells with known antibodies and watching for agglutination, the clumping that signals a positive reaction. Anything that interferes with that reaction can produce a wrong result.
One documented case involved a patient with autoimmune hemolytic anemia (AIHA) whose own body was producing an antibody against the D antigen. This autoantibody caused the patient’s cells to clump in the presence of anti-D testing reagents regardless of their actual Rh status, leading to a false identification. The problem was compounded by a prior blood transfusion of a different type, which added donor red cells to the mix.8PubMed. Faulty blood typing misled by auto anti-D in AIHA Cases like this are rare, but they demonstrate that a single blood typing result is not infallible, and that a change in reported Rh status might reflect a laboratory issue rather than a true biological shift.
Clinicians are trained to investigate when a patient’s blood type does not match a previous record. The resolution usually involves more specialized testing, such as washing the red cells to remove interfering antibodies, using different reagent sources, or performing genetic testing. The takeaway for patients is simple: if you are told your blood type has changed, it is reasonable to ask for confirmation with a second method before assuming it has.
Bacterial Infections and Acquired Antigens
Infections can also create temporary blood type discrepancies, though this has been documented mainly in the ABO system rather than the Rh system. Certain bacteria, particularly gut organisms, produce enzymes that modify the sugars on red blood cells. In two reported cases, elderly patients with blood type A were found to have an “acquired B antigen” during active bacterial infections, one caused by E. coli and the other by Pseudomonas septicemia.9PubMed. Acquired B antigen: an ABO typing discrepancy successfully reversed by transfusion with type A red blood cells The bacterial enzymes chemically altered the A antigen so that it cross-reacted with anti-B reagents, making the patients appear to have a B component to their blood type that was not really there.
The acquired B phenomenon resolves once the infection is treated. It does not reflect a change in the patient’s underlying genetics or permanent blood type. It is an ABO-system quirk and does not apply to Rh status in the same way, since the D antigen is a protein rather than a sugar, and bacterial enzymes that target it have not been described. Still, it is one more reason why a blood type result during acute illness can differ from one obtained when the patient was healthy.
Chimerism and Mixed Blood Types
A much rarer phenomenon is chimerism, where a single person harbors cells with two different genetic makeups. This can happen naturally, most commonly when fraternal twin embryos exchange blood cells in the womb. A chimeric individual might have two populations of red blood cells, each expressing a different blood type. On a standard blood typing test, this shows up as “mixed field” agglutination: some cells clump and some do not, giving ambiguous results.
One case report described a dispermic chimera, a person formed from two separately fertilized eggs that fused into one embryo, whose B antigen typing showed mixed field agglutination that could easily have been mistaken for a rare B subtype.10PubMed Central. A dispermic chimera with mixed field blood group B and mosaic 46,XY/47,XYY karyotype Chimeric individuals might receive different blood type results at different times depending on which cell population predominates in the sample or how the lab interprets the mixed reaction. In the Rh system, a chimera could theoretically have some cells that are D-positive and others that are D-negative, producing confusing and inconsistent results.
Passenger Lymphocyte Syndrome After Organ Transplant
Solid organ transplants do not replace the recipient’s bone marrow the way stem cell transplants do, so they do not change blood type in the same fundamental way. However, they can create temporary blood type complications through a process called passenger lymphocyte syndrome. When a donated organ is transplanted, it carries along immune cells from the donor. If the donor and recipient have different blood types, those donor lymphocytes can produce antibodies against the recipient’s red blood cells, causing a form of hemolytic anemia.11PubMed Central. Passenger lymphocyte syndrome – Epidemiology, pathogenesis, diagnosis, and future directions: A review
Passenger lymphocyte syndrome does not change the recipient’s blood type itself, but it can destroy enough of the recipient’s red cells that blood typing becomes temporarily unreliable. The syndrome is self-limiting because the donor immune cells eventually die off without ongoing support from donor bone marrow, but during the active phase it can complicate blood transfusion management.
Why Rh Status Matters So Much in Pregnancy
The Rh system’s clinical significance is most acute in pregnancy. If an Rh-negative mother carries an Rh-positive baby, her immune system can produce antibodies against the baby’s D antigen. This can lead to hemolytic disease of the fetus and newborn, a condition in which the mother’s antibodies cross the placenta and attack the baby’s red blood cells.12The Review of Diabetic Studies. Rh Blood Group System: Clinical Significance, Laboratory Testing, and Transfusion Safety Prevention involves giving the mother anti-D immunoglobulin (commonly known by the brand name RhoGAM) during and after pregnancy.
Here is where the question of changing Rh status has a practical edge. With newer technology, a pregnant woman’s blood can be tested for fragments of fetal DNA circulating in her bloodstream, which reveals whether the baby is Rh-positive or Rh-negative. This cell-free DNA approach was first described in 1993, and two U.S. companies have recently introduced it as part of their noninvasive prenatal testing panels.13PubMed. The use of free DNA for fetal RHD genotyping in the Rh negative pregnant patient-the time has come If testing shows the fetus is Rh-negative, the mother can be spared unnecessary RhoGAM injections. If the fetus is Rh-positive, the standard prevention protocol proceeds. The ability to determine fetal Rh status from a maternal blood draw has made pregnancy management more precise, avoiding a blanket assumption that every Rh-negative mother needs prophylaxis.
The Evolutionary Puzzle of Rh-Negative Frequency
Given how dangerous Rh incompatibility can be in pregnancy, you might expect natural selection to have pushed Rh-negative frequency to near zero. Yet in European populations, the deletion variant that causes Rh-negative status is remarkably common, with a frequency around 0.43 in some study populations.14PubMed Central. Evolutionary genetics of the human Rh blood group system That is surprisingly high for a gene variant whose main known effect is to create a potentially lethal mismatch between mothers and babies.
Researchers have tested whether some hidden benefit of being Rh-negative might explain its persistence, similar to how carrying one copy of the sickle cell gene offers malaria protection. When investigators looked for signatures of positive selection at the RHD gene using genomic data from multiple populations, they found no evidence of it. The best current explanation is that the deletion rose to high frequency through genetic drift or ancient population bottlenecks, not because it offered any survival advantage.14PubMed Central. Evolutionary genetics of the human Rh blood group system Outside of Europe, Rh-negative frequency drops sharply. In East Asian and sub-Saharan African populations it is much rarer, which aligns with the drift hypothesis rather than a universal selective pressure.
Engineering Blood Type With CRISPR
One of the more striking developments in this space is the use of gene-editing technology to deliberately create Rh-negative blood cells in the laboratory. Researchers have used CRISPR-Cas9 to knock out the RHD gene in human induced pluripotent stem cells, then coaxed those edited cells into developing into red blood cells. The resulting lab-grown red cells tested negative for the D antigen and did not react with anti-Rh D reagents, confirming a successful conversion from Rh-positive to Rh-negative at the cellular level.15PubMed Central. Generation of Rh D-negative blood using CRISPR/Cas9
A separate research group took this approach further, using CRISPR not just on the Rh system but also on ABO antigens, producing cells that were effectively type O-negative, the universal donor type. Their method, working with blood-forming stem cells rather than pluripotent stem cells, achieved nearly complete conversion to cells lacking both AB and Rh antigens.16Human Molecular Genetics. CRISPR-Cas9-driven antigen conversion of clinically relevant blood group systems This is still laboratory work, nowhere near clinical use. Growing enough functional red blood cells from edited stem cells to produce a transfusable unit of blood remains a major technical hurdle. But the proof of concept is there: blood type, including the positive-or-negative distinction, can be changed at the genetic level with current technology, at least in a dish.
The potential long-term application is significant for rare blood type shortages. Universal donor blood is always in demand, and the ability to manufacture it from any starting blood type could eventually ease supply constraints. For now, though, the work serves mainly to illuminate just how precisely the D antigen system can be manipulated, reinforcing that Rh status is a product of a single well-understood gene rather than some mysterious, immutable property of the blood.