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Blood type AB son with type O parent?

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I am type O and my son is AB blood type. He wasn't switched at birth and he certainly came out of me. All typing is correct. What gives?
Posted Sun, 22 Apr 2012 in General Health
Answered by Dr. Sumit Bhatti 1 hour later

Thank you for your query.

1. Though it may seem that a Blood Type O Mother cannot have a Blood Type AB child even if the Father is Blood Type AB, since one gene has to be from each parent, under the following conditions, this can happen:

a) You are genetically a Blood Type A or B. However, your h antigen / substance is defective and hence during blood typing, you appear as a Blood Type O.

b) You are genetically a Blood Type A. There are many subtypes of A, which are so weak that they show up as Blood Type O.

c) You and / or the father is a Bombay phenotype. Bombay Blood Type is genetically an A or B. Here, too, faulty h antigens/ genes make each parent appear Blood Type O on routine testing.

d) Your son is exhibiting Blood Chimerism, especially if you have had an IVF. Many pregnancies are multiple to begin with, where the other embryos become nonviable and disappear. Sometimes, genes may be shared between them and thus the child has an entirely different Blood Type.

2. You should all re-test in the light of the above. ABO Blood Type is a complex system an not as straightforward as it seems. Knowing the Father's Blood Type may also help solve this issue.

3. You may never be able to prove maternity or paternity on the basis of the ABO Blood Type alone. There are other systems as well as DNA Typing available for this.

Hope I have answered your query. If you have any follow up queries I will be available to answer them.


Above answer was peer-reviewed by
Follow-up: Blood type AB son with type O parent? 18 hours later
Hello Doctor,

When recently discussing this situation with my mother, she informed me she is AB+ without a doubt and always has been (recent surgeries and blood donations) and mine keeps coming up O+. My son was military tested and also has given blood. This isn't about paternity for me or my son. Trying to figure this out medically without putting doubt in someone's head. My father has said he is O or A positive and I didn't push it. So, what I am now looking at is that the original issue is with me and I would be the one not registering a correct blood type and should pursue testing! Defective H, Bombay blood, Weak A or Chimerism are my apparent possibilities! I have some type of A or AB (pending my dad's type) through weak blood, very rare blood type, or genetics (more than 1 set of DNA). Am I understanding this correctly?

Answered by Dr. Sumit Bhatti 5 hours later

Yes, you have understood correctly. If your mother is an AB Blood Type, then the possibility of your Blood Type being a pure O is theoretically nil. You are now a part of this paradox.

Above answer was peer-reviewed by
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