A "rare blood awareness week" begins Monday in France, the first campaign on this subject organized by the French Blood Establishment (EFS), a public body and the sole operator for blood collection in the country.

The traditional classification (ABO with rhesus positive or negative) includes eight groups, which correspond to 98% of transfusion needs: A +, A-, B +, B-, AB +, AB-, O +, O-.

But this classification is not enough to reflect the real diversity of blood groups.

There are in fact 380, including 250 considered rare, listed according to other classification methods.

You can therefore be a carrier of rare blood even if you are placed in one of the eight classic categories.

Finding out requires in-depth analyzes of fine genetic characteristics.

Some groups are extremely rare.

This is the case with those called Bombay (one person in a million in Europe) or Rhesus null (about fifty individuals in the world).

Rare groups "are defined by two elements: their frequency, less than 0.4% in the general population, and the fact that there is no alternative for transfusion", explains Professor Jacques to AFP. Chiaroni, from the EFS.

In France, where for genetic reasons the rare groups are, according to the EFS, mainly present in people with African roots (Africa but also the Antilles or the Indian Ocean), it is estimated that 700,000 to one million carriers of a rare group. and only 10% know it.

Greater diversity in Africa

In the event of a transfusion, these people should receive blood as close as possible to their own.

Because whatever our group, incompatible blood "renders the transfusion ineffective at a minimum, or even at worst can kill," recalls Professor Chiaroni.

The specificity of a blood group for a given geographic region is the result of human adaptation to its environment, which has shaped its genetic characteristics over the centuries.

Blood test in Paanenefla near Sinfra in Ivory Coast, October 11, 2019 ISSOUF SANOGO AFP

"Genetic diversity is greater in Africa, where the population is older since it is there that Man appeared", underlines Jacques Chiaroni.

The worldwide dissemination of these blood groups is linked to migration, and all populations are concerned.

The scientist cites a group present in Eurasia whose "distribution sticks with the Mongol expansion in the thirteenth century".

A group rare somewhere is not necessarily so elsewhere.

"I am rh negative, and in China I am untransfusable", because this characteristic is rare there whereas it concerns 15% of Europeans, notes Pr Chiaroni.

Due to lack of stock, it may be necessary to import rare blood.

This is what happened recently for a child who was to undergo a marrow transplant in France and for whom the EFS brought blood from the United States.

"Avoid stigma"

A rare blood carrier can be spotted by chance, during a pre-transfusion work-up or a screening campaign.

His siblings are then approached, because they are likely to have the same blood type.

The needs are particularly acute for sickle cell anemia, a blood disease which mainly affects people of African origin and requires periodic transfusions.

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31-year-old West Indian Laëtitia Defoi suffers from it and has a rare blood type, although she is classified B +.

"Two years ago, my body rejected B + blood which did not correspond exactly to my group," she told AFP.

"Sickle cell disease causes bone complications, with additional operations and transfusions. If I walk, it's partly thanks to transfusions," adds the young woman, whose association, Drepacare, supports the sick.

A public health issue, the issue of rare bloods is a delicate one.

It can lend itself to racial, even racist interpretations, wrongly concluding that the blood between blacks and whites is incompatible.

"It is essential to avoid stigmatization, insists Professor Chiaroni. Every day we have European populations transfused with blood from donors of African origin and vice versa."

© 2021 AFP