Not long ago, a precious packet of blood traveled more than 7,000 miles by special courier, from America to Australia, to save the life of a newborn. Months before the delivery date, a routine checkup of the mom-to-be had revealed that the fetus suffered from hemolytic disease.
Doctors knew that the baby would need a blood transfusion immediately after delivery. The problem was, the baby’s blood type was so rare that there wasn’t a single compatible donor in all of Australia.
A request for compatible blood was sent first to England, where a global database search identified a potential donor in the United States.
From there, the request was forwarded to the American Rare Donor Program, directed by Sandra Nance. The ARDP had compatible frozen blood on hand, but Nance knew that a frozen bag might rupture in transit.
So her organization reached out to the compatible donor, collected half a liter of fresh blood, and shipped it across the Pacific. When the mother came in to give birth, the blood was waiting. “It was just magic,” Nance says.
You’re probably aware of eight basic blood types: A, AB, B and O, each of which can be “positive” or “negative.” They’re the most important, because a patient who receives ABO +/– incompatible blood very often experiences a dangerous immune reaction.
For the sake of simplicity, these are the types that organizations like the Red Cross usually talk about. But this system turns out to be a big oversimplification.
Each of these eight types of blood can be subdivided into many distinct varieties. There are millions in all, each classified according to the little markers called antigens that coat the surface of red blood cells.
AB blood contains A and B antigens, while O blood doesn’t contain either; “positive” blood contains the Rhesus D antigen, while “negative” blood lacks it. Patients shouldn’t receive antigens that their own blood lacks—otherwise their immune system may recognize the blood as foreign and develop antibodies to attack it.
That’s why medical professionals pay attention to blood types in the first place, and why compatible blood was so important for the baby in Australia. There are in fact hundreds of antigens that fall into 33 recognized antigen systems, many of which can cause dangerous reactions during transfusion.
One person’s blood can contain a long list of antigens, which means that a fully specified blood type has to be written out antigen by antigen—for example, O, r”r”, K:–1, Jk(b-).
Try fitting that into that little space on your Red Cross card.