I try and summarize http://etss.u-strasbg.fr/images/Questionnaire2006.pdf below (sorry I don’t have a blog so I pollute others’ with my long comments) :
-”do you feel like you need a viral test ?”
-”do you have HIV or [list]?”
-”have you ever received blood, organs, been operated on, did you take Soriatane® ?”
-allergies, malaria
-”do you have relatives with a disease [from a list] ?”
-”did you travel out of Europe last three months ?”
-”have you ever been out of Europe for more than three months ?”
-”stay for more than one year in great Britain between 1980 and 1996 ?”
-”during the last four months : did you take medicines, been operated on, been vaccinated, have some very common diseases [from a list], been pierced, in contact with human blood (even by projection !) ”
-many others
-”did you read it all ?”
-”did you ever take drugs, ever have sexual relations between males, were you ever paid for sex [etc] ?”

Many questions are asked several times, and we’re even told that we can change our mind after the donation -the whole process keeping the donor anonymous to the receiver.

All refuse donations by people who were sick lately (where what lately means varies depending on the illness) and most deny donations by people who regularly take medicine. All refuse donations if you take certain medicine (like anti-depressants or certain pain treatments).

The exact rules are partly dictated by the applicable law (which is different from country to country) and are otherwise derived from experiences they made (certain groups have a higher risk of AIDS for example) or from rules their respective blood recieving organisation set up. Blood is rarely “marketed” directly by the organisation receiving your donation, at least in Germany. The Red Cross seems to be the big exception here until you carefully look at the organisational structure, which uses a bunch of closely related and similarly branded companies (charitables though).