I use to donate blood all the time, they have trouble finding my veins too sometimes - and they turned me away a few times for being anemic.
I am Rh negative - blood type A negative.
My Doctor doesn't want me to donate blood anymore, while he is giving me Synthroid to treat my hypothyroidism.
My son donated blood at college just last week. He is also RH negative - so we have a not so common blood type.