Blood type and a quick heads-up

Back in high school, we all donated blood and were handed these little donor cards as a thank you...

It turns out I'm type B—anyway, there's this specific note printed right under my blood type and Rh factor. I'm trying to figure out what exactly it's telling me...

The note says: D negative in MSNBC

So, I went in to donate blood again today, and I couldn't help but ask what the whole process actually signifies...

The doctor's explanation? Since my Rh factor is negative, this serves as one of the standard methods for confirming that negative status!!! 🙂

What are the different blood types out there, and how common are they?

http://www.cdc.gov/bloodsafety/index.html