My doctor told me I have blood-type h-h. What does this mean?
This means that you've got the rarest blood type in the world.
This very rare phenotype is generally present in about 0.0004% (about 4 per million) of the human population, though in some places such as Mumbai (formerly Bombay) locals can have occurrences in as much as 0.01% (1 in 10,000) of inhabitants: hence also the name Bombay phenotype.
Normal blood group analysis may mark this as O type, but in reality the red blood cells of hh phenotype possess a distorted version of the basic ABO antigen H or substance H. This means transfusion of regular O type blood in body of hh individual will lead to coagulation.
Given that this condition is very rare, any person with this blood group who needs an urgent blood transfusion will probably be unable to get it, as no blood bank would have any in stock. Those anticipating the need for blood transfusion may bank blood for their own use, but of course this option is not available in cases of accidental injury. For example, in 2017 only one Colombian person was known to have this phenotype and it was needed to import blood from Brazil in order to receive a transfusion.
Sources : Colprensa (2017-07-13). "La primera importación de sangre salvó a una niña paisa" [The first import of blood saved a paisa girl]. El Colombiano (in Spanish). Medellín. Retrieved 2017-07-13.,
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