Blood donation
Blood donation is the process of giving blood to be used for medical purposes, including blood transfusions. Some blood donors are able to give blood platelets by apheresis; the process is lengthier (around two hours per donation) but can be undertaken every four weeks, rather than around three times a year for regular donation.
Some religious groups such as Jehovah's Witnesses do not agree with the donation or receipt of blood for conscientious reasons.
High-risk donors
People with a high risk of spreading HIV are not allowed to give blood. For prostitutes, etc., they avoid risky behavior for one year.
For male homosexuals, any sexual encounter with another man since 1977 disqualifies them permanently.[1] In March 2010 a group of senators asked that the FDA lift the ban. [2]
Further information
US & Canada: http://www.bloodcenters.org/aboutblood/bloodfacts.htm
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