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What is the Rarest Blood Type?

This article talks about the rarest blood type: Bombay, and contains a brief story from Dr. Cohen about other blood types.
Close up of red blood cells
© Created for Mini Medical School by JJ Cohen 2014 Creative Commons Attribution-Noncommercial-Share Alike 4.0 License

What is the rarest blood type?

The rarest blood type is Bombay.

A patient who came to the King Edward Hospital (KEH) in Mumbai, require a blood transfusion. He was typed as type O because they found no A or B on his red blood cells, and his plasma had anti-A and anti-B antibodies, as expected.

But when they started to give him a transfusion of type O red cells, he developed a transfusion reaction, and fortunately for him, they were able to stop the transfusion in time.

Later they did much more detailed typing of his red cells, and found that they had no A or B, but also: not even O! He was the first person identified with this condition; it was 1952.

Why is Bombay the rarest blood type?

People with the Bombay blood type lack the enzyme that adds the last sugar in the O antigen (the red triangle).

You need that to be able to add the final A or B sugars to the top yellow circle, so they always test as O regardless of what their ABO genetics actually are. But even O red cells, having the extra sugar, are foreign to Bombay people!

What happens when a transfusion is needed?

They have two choices when a transfusion is needed. If there is plenty of money for it, they can donate units of red cells to themselves when they are healthy.

These can be put in special protective solutions and frozen at ultra-low temperatures, where they will keep for years.

Or, they can find a blood bank with a unit or so of Bombay blood on hand. A city- or region-wide network is usually in a place that can expedite the search.

Only one or two people in a million might have this worldwide, though there is some enrichment for the Bombay allele in Indian populations.

Here are a couple of Bombay Blood Type websites you might find interesting: A chapter from a text called Blood Groups and Red Cell Antigens by Laura Dean from the National Center for Biotechnology Information (NCBI), National Library of Medicine, National Institutes of Health, and it’s actually fun reading! A community website for people with the Bombay type, including a list of people seeking units of blood.

© Created for Mini Medical School by JJ Cohen 2014 Creative Commons Attribution-Noncommercial-Share Alike 4.0 License
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