SARA, the rarest blood group in the world

The blood groups A, B, AB and O, which we already know – negative or positive – are only the most popular categories. For example, until recently we saw that in the 50 years after it was discovered, only about 50 people worldwide had the Rh zero blood type.

At least according to official information. This type of blood, which does not contain all of the antigens of the Rhesus (Rh) system, is known as “golden blood” and was first discovered in an Australian native in the 1960s. However, there is an even rarer blood group.

SARA, an antigen also discovered in Australia

In 1990, researchers from the Australian Red Cross Blood Service discovered a new antigen in the red blood cells of a blood donor named Sarah Culhane. This was then called “SARA”. The SARA antigen did not match any of the known families of blood group antigens. Some of Sarah’s unusual blood was frozen and stored.

About 20 years later, in 2010, the Australian blood organization (Lifeblood) received blood samples from its Canadian colleague from a family whose baby had needed a massive blood transfusion after a miscarriage. Since no compatible blood was found, Canadian doctors turned to their Australian counterparts to find out if the newborn baby had an identical blood type to Sarah.

Photo credit: Shutterstock / New Africa

The fetus’s immune system is attacked by that of the mother

Australian doctors tested mother and father plasma on a panel of more than 50 rare cell types archived in the country’s blood banks. Laboratory tests showed the mother’s blood was SARA negative. The antigen then attacked the immune system of the fetus whose blood type was SARA positive.

Photo credit: Shutterstock / angellodeco

“The father was SARA positive and the mother SARA negative. She had an antibody that reacted strongly with the baby’s SARA-positive cells. He needed a double exchange transfusion to recover, “said Rhiannon McBean, postdoctoral research and development fellow at Lifeblood and the University of Sydney.

A very, very rare blood type

As stated by, the SARA antigen is now officially recognized as a new blood type by the International Society for Blood Transfusion. It is a very rare antigen as it is only known by two families worldwide. “Of the 5,000 blood samples we tested in the lab, all of them had normal blood types like A, B, AB, or O, which we come across frequently,” added McBean, according to

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