In the past few years I have been receiving several emails from people stating that their blood types have been diagnosed differently in different tests. This is not uncommon. Here are the 4 reasons why you may have gotten different results in your tests:
1) Human error
It is very sad, but human error does top this list. Doctors and nurses are often overworked and these things can happen.
One prime example is where out of 262 active duty Air Force personnel, eleven errors in blood type information were identified, including seven Rh type errors and six ABO typing errors.
If you have had two different results from two different tests, find a third place to get your blood type tested and make sure to let them know what has previously happened to ensure that they will take extra care to properly type you.
You can also order a test to do it yourself.
And if you decide to donate blood, it is less likely that donation stations will mistype you as in their case such an error could result in the death of a patient.
2) Your antigens can have weak expressions
You can be a weak A or a weak B.
In those cases, your A or B could express itself so weakly, that some blood type tests show you as being blood type O while others will show you as the antigen you express weakly, either A or B.
Weak D
In serologic testing, D positive blood is easily identified. Units which are D negative are often retested to rule out a weaker reaction. This was previously referred to as Du, which has been replaced. By definition, weak D phenotype is characterized by negative reaction with anti-D reagent at immediate spin (IS), negative reaction after 37 °C incubation, and positive reaction at anti-human globulin (AHG) phase. Weak D phenotype can occur in several ways. In some cases, this phenotype occurs because of an altered surface protein that is more common in people of European descent. An inheritable form also occurs, as a result of a weakened form of the R0 gene. Weak D may also occur as “C in trans”, whereby a C gene is present on the opposite chromosome to a D gene (as in the combination R0r’, or “Dce/dCe”). The testing is difficult, since using different anti-D reagents, especially the older polyclonal reagents, may give different results.
The practical implication of this is that people with this sub-phenotype will have a product labeled as “D positive” when donating blood. When receiving blood, they are sometimes typed as a “D negative”, though this is the subject of some debate. Most “Weak D” patients can receive “D positive” blood without complications. However, it is important to correctly identify the ones that have to be considered D+ or D−. This is important, since most blood banks have a limited supply of “D negative” blood and the correct transfusion is clinically relevant. In this respect, genotyping of blood groups has much simplified this detection of the various variants in the Rh blood group system.
Partial D
It is important to differentiate weak D (due to a quantitative difference in the D antigen) from partial D (due to a qualitative difference in the D antigen). Simply put, the weak D phenotype is due to a reduced number of D antigens on a red blood cell. In contrast, the partial D phenotype is due to an alteration in D-epitopes. Thus, in partial D, the number of D antigens is not reduced but the protein structure is altered. These individuals, if alloimmunized to D, can produce an anti-D antibody. Therefore, partial D patients who are donating blood should be labeled as D-positive but, if receiving blood, they should be labeled as D-negative and receive D-negative units.
In the past, partial D was called ‘D mosaic’ or ‘D variant.’ Different partial D phenotypes are defined by different D epitopes on the outer surface of the red blood cell membrane. More than 30 different partial D phenotypes have been described.
Microchimerism is defined as the presence of a small number of cells that originated from another individual and are therefore genetically distinct from the cells of the host individual.
This phenomenon is also very rare, but it can happen for example between twins where cell tissue is being exchanged. It would mean you are carrying different genes for different blood types within your cells.
4) Your blood type has changed
This is extremely rare, yet there are 3 reported cases which I am aware of where someone’s blood type has actually changed regarding both, the rh factor and the ABO type:
From blood type O positive to O negative
From blood type O negative to O positive
From blood type A to blood type O
Have you ever had a blood type test done just to receive a different result from a previous test?
We would like to hear from you and find out what the reason turned out to be.
My blood type has never changed. I’m b-. My daughter my second daughter however recently discovered when trying to donate blood platelets that she, while o+, is carrying antibodies from my blood, and can never give blood. She is 26. She had to stay in the hospital for five days after her birth due to antibodies and jaundice, but was seemingly fine and sent home. I had no idea it was still an issue until she called me a month ago. Is this similar to microchimerism? Thanks!
Was she told that she had antibodies to human platelet antigens (HPA) and/or human leukocyte antigens (HLA)?
All women giving platelets by apheresis are tested for these (across the world). If these are HLA/HPA antibodies it should not mean that she cannot donate whole blood via the usual blood donation route, just not platelets.
Or did she have a blood transfusion during those five days in hosptal as a baby (a cause of HLA antibodies)? And/or did she have thrombocytopenia when she was born (low platelets)? Thrombocytopenia in babies can result from the mother developing antibodies to fetal platelets (if I have understood that correctly).
My daughter is a B- Negative , she was stress born one month premature and i had Toxemia, which is what they called back in 1988.I am a an 0+ and when i had my first daughter in 1988 i was 17 years old, so i was fairly young to have so many complications during pregnancy.I started bleeding at five months into my pregnancy, they said stress.My daughter was jaundice had to be put under bilirubin lights for three days and her lungs were not fully developed yet.I know they say there are no complications with the mother being RH positive, i find that for me it was troubling, sick all through my pregnancy.My daughter is grown up but has many ailments, she recently told me her blood came back as an O+ .I asked her if she was sure and she said “the nurse told me that maybe when i was younger , they had made a mistake”, we both knew this wasn’t true she has had surgeries for colon ulcers and her blood has always been as stated when she was a baby B-.Her latest doctor check-up she back to her being B-, what is ironic is it was the same nurse at the same hospital that took the last blood sampling.Just Strange.I wanted to add my Mother is a RH- and my Father was an RH+, my Daughter’s Father is a B-, like my daughter. What i am curious to know is those that RH+ with a recessive Negative trait, where does this recessive gene hide within us?
The reason why your daughter had jaundice as a newborn was probably because of your O and her B and is nothing to do with your respective RhD status. This is not uncommon for O mothers with non-O babies. You have antibodies to both A and B and hence your B antibody attacked your daughter’s B antigen red cells. The ensuing battle made your daughter ill.
We develop our ABO antibodies upward from 6 months to 10 years as the sugars on the ABO antigens are similar to those found in our environment, perhaps on e.g., our gut biome, pollen etc. This is why O plasma can only be given to O patients.
We inherit our blood group genes from both parents. You inherited an RHD gene from one parent and didn’t inherit the RHD gene from the other. So you are genetically a D:d, where “d” is used as a marker of the absence of the RHD gene. When you daughter was conceived neither parent passed an RHD gene to her, so she is a d:d and hence is Rh (D) negative. You had 50% chance of passing to her your RHD gene, then she would have been a D:d like you.
It’s not “hiding”, just absent.
It is not unusual to be absent red cell antigens and hence have no genes to pass on for them. If your daughter’s ancestry is white European then her first five Rh antigens (the “extended Rh antigens) are very likely to be D-C-E-c+e+ (ditto your husband). Whereas 55% of those with black African ancestry are D+C-E-c+e+, which is why my “white” Rh negative red cell units go to “black” sickle cell disease patients for their exchange transfusion treatment . (I am likely not such a good match for the Diego, Duffy and Kidd antigen combinations, which is why more black donors are needed where the donor pool is from predominantly white donors.)
What we should do with our blood is donate it and have an interest in it for its usefulness.
NB That “c+” is why there is no such thing as a “universal donor”. A small % (2?) of the white population are negative for the Rhc antigen and the antibody to Rhc is a cause of severe haemolytic disease of the fetus and newborn. So some women will develop an antibody to an O Rh negative transfusion. That could also be a problem for people who have multiple transfusion treatments and are Rhc negative.
In the UK and many other countries women are given in an emergency red cell O Rh negative red cell units negatve for the K antigen in the Kell group. Antibodies to K kill the fetal precursor red blood cells and 92% of the white population are negative for K and nearly 100% of the black population, (Arab populations are 80% negative for K) . The USA does not take this precaution.
My mother is a Doctor and she checked my blood type during my childhood which came out to be A +ve but when I went for a donation during my adolescence, it came out to be A -ve and I have donated a few more times after that during the years and it has always been A -ve.
Im on here trying to find people in the same situation as my best friend. Her blood type switches between 0 negative and 0 positive. She doesn’t know how often but she is currently having a miscarriage and last week it was 0 positive when she first went and yesterday went back for miscarriage and its 0 negative. They told her its rare and possibly autoimmune and we really don’t know anything about it. But that it changes back and forth.
It could be chimerism, but also be a case of weak-D. In some tests the D shows up, in others it isn’t recognized.
I’m sorry to hear of your friend in peril. Losing a child is incomprehensible! If at any time during pregnancy, she had O- blood type, why did her OBGYN not protect pregnancy with immunosuppressive therapy to save pregnancy called RhoghaM? Please ask Mike, my understanding is that I had not been given Rhogham, more than likely my body would not have supported three pregnancies and babies as father O positive….my body would have aborted fetus…no expert ask Mike Daemon… He would know. Condolences…very sad!!!Your a good friend looking for answers.
I am the same as your friend! This comment is the first I’ve seen of ANYTHING that relates to my experience: I’ve been typed always as an O negative but recently while pregnant /miscarrying my bloods have come back continually as O positive and it’s got me so confused. None of the nurses/docs have believed me about my previous negative typing as it was in a different state and not on their records, I’ve only been told that it can not change. I plan on going back and getting tested in a month or so once my hormones are not impacted by the pregnancy anymore to see if it comes up O negative again..
My real question is though; if it does come back O negative after being typed O positive, am I able to donate blood to be transfused into an O negative person?
I have a mystery. My mom was O negative. I am AB positive. Not sure about my dad, who died in 1996. I was conceived in 1966 and born in 1967, 2 years before RH protocols in 1969.
Am I:
1) an experimental in vitro? In 1966
2) cis-AB
Please help. I’ve never had a transfusion..but I might need one in the future. I will die if they think I’m a ” redl” AB positive ( universal receiver) and if I am Cis-AB, I need to sylf bank my blood. I am trying to get help in the USA to no avail.
I have another surgery planned next year ..but I need to know for sure
Thanks!!
Elizabeth, it isn’t clear from what you have written how you know that you are AB Rh positive. Is this a recent hospital assessment? Similarly your Mum, had she rememberd her from assessment for antenatal care?
You are worrying unnecessarily. Even if you are a cis-AB you are a “real” AB for the purposes of transfusion, that’s your phenotype. Cis-Ab affects inheritence and describes the gentical structure behind a phenotype.
When I was born, I was typed as O positive. When I was in high school, and had surgeries, I was also typed as O positive. I ended up studying for a lab career in college, and when we drew each other’s blood for our blood bank class, I typed as A positive. I was in shock, and wanted to recheck it, but it still came out as A positive. I ran the tests multiple times on myself with the same result. I also had donated blood at that time, and they also typed me as A positive. When I eventually got a job in a blood bank, they allowed me to have my blood drawn, and let me type it, which was fun, since I was able to test for almost the entire panel, since they had the reagents, but I was still typing as A positive. Is it possible that I had a weak A until I was in college and then it finally had fully expressed itself or is it that they didn’t do back typing in the 80’s and 90’s? My parents are typed as A negative and O positive.
I was typed multiple times as AB+, the first time in science class as a junior. We redid the test 2 times, before calling the teacher over. He said, “Don’t tell me what you got, I want to see if I match without a preconceived notion. He also got AB+. 3 times.
Donated blood through the Red Cross for years, until I injured my back, and thought I was not eligible, because of medications I am on. Red Cross also said AB+. Just donated blood 2 weeks ago, and just received my donors card. They say now I am O+. I am 60 – how does this happen?
Time to double check the records.
On my records as a child, I am listed as B+. Now as an adult and about to give birth, I am A+. Wondering if maybe the doctors had originally made a mistake or if it was possible my blood type changed.
Same thing happened to me. I have a medical card glued to my birth certificate from childhood that says my blood type B(III) positive.
At 21, I donated my blood to Red cross and my donor card says A positive.
I’ve been O- Rh- most my life. I needed a surgery a few years ago. Blood was typed three times, result A- Rh-. I can’t get any answers. No blood transfusions, no bone marrow transplants, anything.
Anybody?
As it says in the article, you could be an ABO group A with a weak antigen expression and previous tests have not shown that and have typed you as O.
Better set of reagents in the hospital and a path lab with more care and your A has been revealed. (The Rh negative sign isn’t relevant to this ABO blood group discussion.)
Why were your blood groups originally tested for? (The ABO O result and the lack of the Rh group D antigen.) Was it pn more than one occasion and always the same institution?
Hi, and thank you for your detailed and helpful reply. I have trouble concentrating, so I probably skipped the part about ABO type when was reading at first. Thank you for your patience and clarification.
Back in Soviet Union, since I was born, I was sick a lot with common colds, respiratory illnesses, pneumonia, flu, and spent a lot of time in hospitals, usually a month at a time. I remember a lot of medications by pill, or by injection. As far as I know, nobody ever informed my parents if they would agree to any of the treatments, it was a norm at that time. Apparently, my illnesses were related to second hand smoking in a small enclosed home but nobody could even guess at the time. Things got better when I was a teen and the environment was changed, not on purpose, but a lot of things were explained. I was cured as if nothing ever happened.
Back to the hospital stay history. My mother said their maybe was a blood transfusion, but probably when I was too little to remember. Even if it was the case I remember that the little paper was glued to my original birth certificate when I was about 12, I suppose to help doctors to help me if something were to happen.
Between 12 and 21 I did not have any hospitalizations. Between 12 and 14, I was still a weak child but nothing major.
I donated blood three times and it all came out with different blood type. First was O positive, then turned into A positive and for the last one it was B positive.
Greetings
I have hit the landmark age of 75 and since I just found your website I am jumping on this puzzle of mine for 30 years and hope you have an explanation that I can live with. When was 13 I was hospitilized for bleeding ulcers. I became so distressed when I looked at my medical chart that was at that time in history
hung on the foot of the hospital bed. It said I had no blood, or so I interpreted it, since it had blood type as O-. When I took biology in high school we did our own blood typing and my teacher checked my work ’cause he had not had an O- pupil before. So I know, first hand, I was O-. Even doctor ordered lab work I requested blood type info. O- each time. My 2 sons’ father was AB (don’t know – or +) Years later I am at Red Cross to donate blood and the technicion says I am AB blood type. I argued and they checked it again and swore it was AB. Needless to say, I refused to donate because I didn’t trust their findings.
I have researched everything on the internet about this and still haven’t come close to what happened in my case. I can’t say what blood type my sons are ’cause I’ve never asked them. I’ve never had a transfusion. If anybody at this site reads this and has anything they can pass along to me on this I would very much appreciate it.
Interesting discussion. I used to think my blood was O-. In fact, I have a card with test results from 2008 from a Dutch hospital confirming this, with my name and details on it. I moved to Greece years ago and have donated blood twice here. Both times, they told me my blood type is A+ instead. I recently found the card from the Dutch hospital again, and will take it with me at the next donation to figure it out.
My child hood medical records have stated both B and O blood type.
Diagnosed with septic arthritis as a child. (Not sure if I was sepsis or not.)
As an adult my blood has been tested/recorded as both B and O blood type.
I had 5 liters/5 blood transfusions as an adult.
My blood typing since the blood transfusions has been tested/recorded as both B and O blood type.
I was told I had a rare blood disorder “Chameleon blood.”
Other than the one doctor that told me I was weird (and had Chameleon blood) and retested my blood to find the same results (one time my blood was typed B and one time it was typed O) no one has taken the time to investigate this weirdness.
I am curious to learn more…
the furthest back ABO RH BLOOD GROUP test for myself I could find was 12/3/2018, VALUE O NEGATIVE. I recall having a second test a couple of years later, but cannot find it. Note: I was born in 1965. The only major surgery I ever had was in 1983, spinal fusion/herrington rod for scoliosis. It was bloodless surgery and I have no records nor can I obtain them, I tried.
I donated blood at Red Cross in Santa Ana, CA in October 2023, I received notice from them that I am O POSITIVE BLOOD TYPE. They could never provide information to me as to why my bloodtype had changed from O NEGATIVE to O POSITIVE. I haven’t given blood again since. My doctor has checked twice. my blood Type came back O WEAK D both times (2024 and 7/9/2025. I have an appointment with her September and will ask her her thoughts. I do have suspicious breast calcifications in right breast and will be having a biopsy. Any ideas?
Can’t see that there has been a reply to you yet and I hope that I am not repeating one…
You are a “variant D”. See e.g., https://www.bbguy.org/education/glossary/glw04/
That means that you may be determined as Rh positive as a donor, because you have some D antigen and therefore could cause a transfusion reaction if your red cells go to an Rh negative recipient, but may be classified as an Rh negative as a patient because you could develop antibodies to to a transfusion of Rh positive red cells. I think I am correct that the prevalence of “variant D” in the white European population/those of that ancestry is 2%, so unusul but not “rare”. * In the black population ,again from memory, the figure is 7%.
(Sorry, I missed out a small piece of explanation that might be necessary. “Rh negative” no D antigen of the Rh system on the red blood cells and “”Rh positive” has the D antigen of the Rh system on the red blood cells.)
The first paragraph in this article is very useful, explaiing the differnce between a “weak D” and “partial D”, https://labmedicineblog.com/2016/05/25/how-we-treat-weak-d-and-partial-d-transfusion-recipients/
There is no relationship between this Rh system matter and breast concerns.
* https://laboratoryintern.com/what-is-the-weak-d-antigen/ Maech 2024 gives “approximately 0.2% to 1%”, quoting a 1998 paper. Checkng that figure.