I do not understand why individuals with type O- blood are often called universal donors and those with type AB+ blood are called universal recipients.

My thoughts on this are:

It should be that because O+ blood has all antibodies but no antigens that all other blood types including O- would be incompatible making O not a universal donor - so why is O the universal donor?

Also if O is the universal donor, it should be O+ that is the universal donor and O- that isn't because Rh+ is compatible with Rh+ and Rh-, not just Rh+ or Rh-.

It should also be that because AB- has all antigens and no antibodies that AB is not the universal recipient - so why is AB the universal recipient?

Here is what I would expect from blood group mixtures:

O-A: A clumping in O

O-B: B clumping in O

O-AB: AB clumping in O

and that being true for the reverse order as well AB-A: AB clumping in A

AB-B: AB clumping in B

as well as the one that everybody knows which is A-B: A clumping in B and B clumping in A

I would also expect for Rh compatibility: Rh- with Rh+: Rh- clumping in Rh+

  • $\begingroup$ @Arsak Nominating for re-opening does not happen automatically. This needs to be done by you and decided by the community. $\endgroup$
    – Chris
    Apr 25 '19 at 13:20
  • $\begingroup$ @Chris Thank you for the feedback! I've found that the reputation threshold for close and reopen votes is at 3000, so I'll leave it's up to the higher-rep user to decide. $\endgroup$
    – Arsak
    Apr 25 '19 at 14:11

In blood groups you always need to consider two things: The antigens present on red blood cells (RBC) and the antibodies present in plasma, which lead to clumping of RBCs if they match. Don't mix up the words antigen and antibody! A healthy individual will never have antibodies against the antigens on their own RBCs, but they will have antibodies against antigens which are not present on their own RBCs. (*)

Also always remember that blood transfusions consist only of RBCs! The plasma and antibodies are removed. If you mix blood of two people directly, all combinations will coagulate unless the blood types are identical. Thus, when thinking about donor and acceptor match, you have to consider the acceptor's antibodies and the donor's antigens - nothing else.

Finally, Rh+ means RBCs have the Rh antigen, Rh- means they don't.

A universal acceptor will thus be someone who has no antibodies at all (because their antigens don't matter - they receive no antibodies from the donor). This is the case if the RBCs have all antigens: AB+

A universal donor will be someone whose RBCs have no antigens at all (because their antibodies don't matter, they get removed before transfusion): O-

As a side note: The ABO system and Rh are only the two most dangerous blood groups when they are mismatched. There are many more RBC antigen types (around 35) and in fact hospitals will consider several of these when matching donors and acceptors.

(*) We don't completely know why we make antibodies against antigens not present on RBCs yet. One hypothesis is that the bacteria in the intestines produce antigens which 'look' similar to our blood antigens. Also, this only applies to the A/B/O antigen. All other antigens work like normal antigens such as bacterial ones - after your immune system has seen them the once, you have antibodies against them.


O- should be the universal donor not O+because when rh- blood is given to rh+ person ,the rh+ person can not make antibodies against rh- blood because there are no rh antigens in the rh- blood.(So what will rh antibodies be made against ?)

Now I think u can figure out about why AB+ is the universal recipient !

  • $\begingroup$ this I think is why it should be O+ that is the universal donor. You see O- is only compatible with O-, B-, A-, and AB- from the Rh compatibility and ABO compatibility combined whereas O+ is compatible with O+, B+, A+, AB+, O-, B-, A-, and AB- as far as donating and as far as recieving these are the compatibilities. O+: O-, O+ and O-: O- so already O+ is compatible with more blood types than O- is on both the donor side and the receiving side. $\endgroup$
    – Caters
    May 26 '14 at 16:10
  • $\begingroup$ No..if you give O+ blood to a person with -ve blood group, that person will make antibodies against the rh antigens on O+ RBC. But if you give O- blood to any blood group they can not make antibodies (reason explained above. ) so your notion that O- is compatible only with negative blood groups is wrong. Receiving and donating compabilities for a blood group are different. You can NOT say that if O+ can receive blood from O-, it can donate blood to O-.. $\endgroup$
    – biogirl
    May 27 '14 at 0:38
  • $\begingroup$ ah but negative blood types have antibodies against Rh antigens in positive blood already there so that means less making of antibodies. Plus when you have a blood transfusion you get an RBC transfusion and a plasma transfusion so there comes the problem of antibodies in plasma. You might also get a WBC transfusion or a platelet transfusion. $\endgroup$
    – Caters
    May 27 '14 at 21:33
  • $\begingroup$ Various factor are considered before blood transfusion. Not only abo and rh+ and - blood group... I am unable to understand what you are asking in the first statemen of the above comment. $\endgroup$
    – biogirl
    May 28 '14 at 0:36

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