Just when you thought you knew all you needed to at this stage in the development of science, a medical marvel steps in to set the record straight. No points for you if you named all of the blood groups. But if we told you we missed out on one of the rarest blood groups in the world? A blood phenotype so rare that it shows up in no more than 4 in every million humans. Blood types are classified basically as combinations of the ABO phenotypes. These include all of the regular blood groups that we usually witness - A, B, O and AB. The compatibility and differences in the blood types rely on the different kinds of antigens and antibodies each contain, and their reaction with each other. This alongside other characteristics like the Rh factor.

The Bombay blood type, h/h or Oh is present in less than 0.0004% of the world's population.

First discovered in 1952 by Dr. Y G Bhide, the Bombay Blood type is largely recognised as the rarest blood group in the world. In an observation of the blood type's reaction with the commonly recognised blood phenotypes, it was found that the Bombay Blood type contained a previously unknown antigen - H.

Antigens A and B are both found to be made from antigen H. So, people with the Bombay phenotype can donate blood but not serve as recipients.

The Bombay phenotype is allowed to donate red blood cells to any of the blood types within the ABO phenotype realm, the reverse, however, is not possible. People with the Bombay phenotype can only receive blood from their own group because of the antigen reactions that may cause defects in the receiver's immunology.