The Truth About The Rarest Blood Type In The World

Do you know your blood type? For many of us, it's a mystery unless you can ask your mom or maybe even find out when you donate blood. Regardless, odds are that your blood type falls under the eight most common, A+, A-, B+, B-, O+, O-, AB+, AB- (according to the American Red Cross). First, a quick lesson in how to read those.

There are four main blood groups — A, B, O, and AB. The first deciding factor is what kind of antigen (basically a molecule) is present on your red blood cells. Folks with A-type blood have the A antigen on their blood cells and the B antibody in their plasma, for instance. For B-types, this is reversed. AB folks have both A and B antigens on their blood cells but none in their antibodies, while O have neither antigen on the cells but both present in the plasma. There is also something called an Rh factor which may be present (represented by the "+" sign) or absent (represented by the "-" sign).

All told, that adds up to the eight most common blood types seen. If you're curious, the most frequently occurring blood type is O+, clocking in at around 37% of the population for Caucasians, 47% of African Americans, 39% of Asian Americans, and 53% of Latino Americans. But there is a blood type not listed here that is far, far more rare.

This rare blood type wasn't identified until 1952

According to The Indian Express, Dr. YM Bhende discovered a new, and extremely rare, blood type in 1952: hh. More commonly known as the Bombay blood group for the city in which it was discovered, those with hh blood type do not express the H antigen — nor do they have A or B antigens.

Globally, only about one in four million people have this type, though, in South Asia, it may be closer to one in 10,000 people, says Financial Express. While those with hh type can donate their blood to those in need with ABO type, they are likely unable to accept blood from A, B, AB, or O donors.

As you can imagine, this imbalance causes a great deal of concern for those with type hh who may require transfusion — especially if traveling, given how few global donors are available outside of South Asia. Even within India, there are currently only 350 available donors and, of those, not all may be able to donate at any given time. Logistically, this blood-type rarity can pose all sorts of challenges within the already often-precarious blood donation network.