The World’s Rarest Blood Type Just Got Even Stranger, Only 3 People on Earth Have It

A blood type found in just three people is shaking up what we thought we knew about human biology. Called B(A), it doesn’t quite fit into the usual ABO system and hints that more hidden variations could still be out there.

For decades, blood types have been treated as a fixed framework in medicine, essential for safe transfusions and basic diagnostics. The system, first mapped in the early 20th century, seemed stable and well understood.

But discoveries like this one show things aren’t so clear-cut. Even now, researchers are still uncovering rare cases that don’t follow the rules, which can complicate real-world medical decisions.

A Strange Mix That Doesn’t Fit The Rules

The B(A) blood type was identified in 2025 during tests at a hospital in Thailand. What caught researchers off guard was the mismatch between expected and actual results. According to findings published in Transfusion and Apheresis Science, these individuals showed mostly B antigens, but also small amounts of A antigens, something standard classifications don’t account for.

The case involved three people: one patient and two donors. Researchers pointed out that:

“ABO discrepancies were distinct between donors and patients even in the same ethnicity,” which is unusual and not something typically seen in routine testing.

This kind of ambiguity can make blood typing less straightforward than expected, especially in situations where accuracy really matters.

A Genetic Twist Behind The Scenes

Digging deeper, scientists traced the anomaly back to the ABO gene on chromosome 9. According to the study, the three individuals shared four specific alleles that hadn’t been seen before in known blood type variants.

These genetic differences affect how antigens are built on red blood cells. The result is a sort of hybrid expression, mostly type B, but not entirely. What stands out is that all three cases showed the same mutations, and those mutations don’t match any previously recorded forms.

“This finding highlighted the influence of the patient’s conditions and therapy on the anomalous ABO typing. Additionally, the B(A) individuals identified in this study carried identical genetic alterations that differed from all antecedent alleles of the B(A) phenotype,” explained the authors.

Rare Blood Types Are Rarer Than We Think

Most people have heard of O negative as the universal donor, but it’s far from the rarest. According to commonly cited figures, only about 50 people worldwide have Rh-null blood, sometimes called “golden blood” because it lacks all Rh antigens.

There’s also Gwada negative, which has been found in just one person. The addition of B(A) brings the number of known blood group variants to 48, showing just how complex this field has become.

“Future studies,” researchers added, “are required to elucidate the structural and functional consequences of the mutated [enzyme] AB transferase.”

Researchers suspect there could be more cases like this that simply haven’t been identified yet. The fact that B(A) turned up in more than one individual suggests it may not be as unique as it first seemed.

Enjoyed this article? Subscribe to our free newsletter for engaging stories, exclusive content, and the latest news.