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Why not just any blood can be transfused
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Blood is not all alike, and that is why not everyone's blood works for everyone. Every red blood cell carries markers on its surface called antigens, which work like labels. The plasma, the liquid part of the blood, carries antibodies, defense proteins that recognize any label that is not the body's own.
The striking part is that these antibodies do not have to be provoked. They appear on their own by around six months of age, without the person ever having received a transfusion. It is as if everyone reached that age with a ready-made list of what they will not accept.
That leads to something very practical. Red blood cells from group O are the ones almost nobody rejects, which is why O is called the universal donor. And someone with group AB, who carries both labels, makes no antibodies against either one and can receive from anyone: the universal recipient.
When the groups do not match, the antibodies stick to the newly transfused red cells and clump them together. Those clumps block the smallest vessels. And there is still another label, the Rh factor, which is classified separately.
In brief
Compatibility depends on the antigens on the red cell and the antibodies in the recipient's plasma.
Every red blood cell wears a label, and the plasma it meets knows which one it rejects.
Anti-A and anti-B antibodies form on their own, with no prior transfusion, by about six months of age.
Group O is the universal red cell donor; AB carries both antigens, makes neither antibody, and is the universal recipient.
If they do not match, the transfused cells clump and block small vessels; Rh is classified separately.
Sources (2)
- OpenStax, Rice UniversityAnatomy and Physiology 2e, 18.6 Blood TypingPublished
- National Center for Biotechnology Information, StatPearls PublishingABO Blood Group System, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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