Se hai mai cercato su Internet il gruppo sanguigno più raro , potresti aver trovato più domande che risposte. La risposta breve: AB negativo è il più raro degli otto gruppi sanguigni principali. Secondo la Croce Rossa americana, meno dell'1% dei donatori americani è AB negativo . Il sangue AB negativo è raro in tutto il mondo, sebbene le percentuali possano variare dallo 0,06% al 3% della popolazione di un paese .
Ma la verità è che ci sono dozzine di altri tipi di sangue molto più rari di AB, e quelli più nuovi, anche più rari, potrebbero ancora essere scoperti.
Prima di entrare in quei gruppi sanguigni super rari, facciamo un passo indietro e guardiamo di cosa è fatto il sangue. Il sangue di tutti, indipendentemente dal tipo, contiene plasma. Sospesi nel plasma sono i seguenti componenti:
- Globuli bianchi, che combattono le infezioni
- Piastrine, che aiutano nella coagulazione
- Globuli rossi, che trasportano l'ossigeno in tutto il corpo e rimuovono l'anidride carbonica
Sulla superficie dei globuli rossi ci sono proteine e zuccheri chiamati antigeni. Servono come marker per caratterizzare ogni tipo di cellula. Ci sono quattro antigeni principali che costituiscono i quattro gruppi sanguigni principali. Sono conosciuti come A, B, AB e O.
A blood types have the A antigen, B blood types have the B antigen, and AB blood types have both A and B antigens. O blood types, however, have neither A nor B antigens. These ABO blood types are further classified as Rh positive or Rh negative. Rh, formerly known as Rhesus, is another protein that is found on the surface of red blood cells. People who have this Rh factor on their red blood cells are Rh positive. Those who do not are Rh negative.
This positive or negative attribute divides the four major blood groups into eight types. The population breakdown in the U.S. is as follows, according to the Stanford Blood Center:
- O positive – 37.4%
- O negative – 6.6%
- A positive – 35.7%
- A negative – 6.3%
- B positive – 8.5%
- B negative – 1.5%
- AB positive – 3.4%
- AB negative – 0.6%
If you're interested in knowing breakdowns for other countries, you can check out this chart at BabyMed.com. Since blood type is genetic, some countries will have more of one blood type than another, depending on the ethnic makeup of the country.
Knowing your blood type is important because it tells medical professionals which blood you can receive in the event you need to undergo a blood transfusion. Receiving the wrong blood type could result in a life-threatening immune response. People who have the AB positive blood type are called "universal recipients," meaning they can receive blood from people with any blood type (but they can only donate to people with their blood type). People with O negative blood are called "universal donors" as their blood type is compatible with all other blood types (but they can only receive O negative blood). People with O positive blood can donate to other positive blood types (like A positive or AB positive), which is about 80 percent of the U.S. population, making O blood in high demand, whether positive or negative.
People with rarer blood types face challenges when it comes to transfusions as finding compatible donors in times of crisis can be difficult.
The Rarest Blood Types
It is possible for someone to have a complete absence of Rh antigens. These people have a blood type referred to as Rhnull. It was first discovered about 50 years ago in an Aboriginal Australian and is extremely rare — less than 50 people have been known to have Rhnull blood.
Rhnull is sometimes referred to as "golden blood." That's because it's worth its weight in gold, at least in the sense that it is considered a "universal" blood that anyone with rare types of blood within the Rh system could use in times of crisis. But the crux is that people with Rhnull blood can only receive blood from Rhnull donors.
There are other types of blood that are as rare, if not rarer, than Rhnull. As of 2019, the International Society of Blood Transfusion, a scientific society that promotes the study of blood transfusions, recognized 360 blood group antigens of which 322 were clustered within 36 blood group systems. It noted that the remaining 38 antigens were currently unassigned to a known system.
These numbers are ever-changing, with new blood group antigens being added to the various blood group systems and, occasionally, antigens being made obsolete based on new data. What all that means is that it's somewhat impossible to determine which is the rarest blood type of them all.
Now That's Interesting
It is very rare — but possible — for someone's blood type to change. This can occur through the addition or suppression of an antigen, which can happen during an infection, malignancy or because of an autoimmune disease. Another cause of blood type changing happens during a bone marrow transplant. People who receive bone marrow from someone with a different ABO type will eventually switch to the donor's blood type.
Originally Published: Dec 16, 2020
