I got a letter from the Red Cross telling me about a blood drive and asking me to come and donate because, the letter said I have a rare blood type.
I’ve been giving blood for a long time now and never really paid attention to my type. I looked at my card and it says I have O- blood.
I was suprised to hear that I had a rare blood type, so I went to look up rare blood types, but O- is not on the list.
What’s the deal here ?
You must have been looking at a rather crappy list, then. Type O blood is indeed the rarest kind, and is especially valuable because it can be given to a person with any type of blood.
Here is an excellent page on blood types.
The New York Blood Center seems to feel that O- is a rare type
From this site, it appears that people with O- blood make up a little less than 8% of the population. But since O- can be used on anybody in a pinch (but not without risk; see the note below the who-donates-to-who table) hospitals probably also run out of it more frequently and need more of it. Your blood in and of itself may not be the rarest, but as a hospital supply it could very well be.
(I’m AB+ myself – as long as the blood comes from an actual human I can probably handle it 
)
There are lots of other blood-type categories besides the ABO system. The most well-known and important is the Rh factor, positive or negative. O-negative, IIRC, is a “universal donor” type, and can donate blood to anyone without causing a reaction. Your Rh type is probably on the card.
Blood is grouped into types (A, B, AB, and O), but also into various subtypes. Most likely, you have a rare subtype that is particularly desirable to the Red Cross.
You might want to ask your local Red Cross if you can get a copy of their typing test results and ask them to explain what they mean. (I’ve done this for other tests that’ve been run on donated blood, and my local group was happy to do it.) If nothing else, you can ask for a copy of the report and have your doctor explain it.
Robin
O- may be rare, but type O blood (which includes O+) is actually the most common blood type.
Not only is it on the card, but she told us what it is. O negative means that her blood is O in the ABO system, and it’s Rh negative. O can donate to any of the ABO types with minimal risk, and Rh negative can donate to Rh positive with minimal (or none at all?) risk, so OB- is the universal donor, at least as far as the two most important typing attributes are concerned.
By rare they probably also meant “in short supply”. Since O neg blood can be given to anyone regardless of ABO/Rh type it’s the most frequently used in trauma situations and blood banks are commonly short on O negs because of that.
The rarest ABO/Rh, in the U.S. at any rate is AB negative.
The most common types are A pos and O pos.