Why Doctors do not donate blood?

Why Doctors do not donate blood? are there any disadvantages?Why Doctors do not donate blood?
Really it is not true. There will be a basis for that. because Doctors are always contact next to patients. So there may be some possibilities to enter some germs to their blood and can not be identified earlier about 3 days. So better Donate blodd if they did not touch patients for few days.
they do donate blood
the doctor I know do donate blood
I think it adjectives depends on what field of tablets they are in. If they are contained by contact with infectious diseases on a day after day basis, I don't reckon it would be a good model for them to donate blood since most diseases take an incubation time of at smallest 3 days to make one 'notice' that they are sick.
How you know they do not donate blood? Any evidences?
I've donated blood 18 times so far. There are copious other doctors who regularly donate blood.