According to the NHS, there are 36 different blood groups and eight "main blood types." The latter consists of the familiar-sounding ones like O, A, B, and AB (positives and negatives), but let's talk rare. Among this group, the rarest is AB negative — just 1% of the population has this type of blood, though that's actually pretty widespread compared to some of the other types.
The NHS says that of their 830,860 donors, Sue Olds from Cornwall is the only one with a -D- blood type. There's also a single person with KL- and one with Hy-, but the NHS claims it's the -D- that's super valuable, as it can be given to a wide range of recipients with no side effects. There's also what MedicineNet calls the "golden blood type." It's more scientifically called the Rh null blood group, and with fewer than 50 people in the world having it — and only nine of those people regularly donating it — it's the rarest blood type of them all.
What makes that blood type difference is that there are no Rh proteins on the red blood cells, which makes them a universal donor. Though this is great, it comes with a huge problem: Anyone who has Rh null blood can only receive a blood transfusion from another Rh null person, and given how rare they are, it's a physical feature that could very quickly become deadly.
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