There was some discussion[0] on HN a few weeks ago organizations (like the Red Cross[1]) not accepting donations from patients who require therapeutic phlebotomy (hemochromatosis patients, for example) because their donation provides the donor a benefit (and therefore isn't strictly altruistic). That sent me down an interesting rabbit hole of reading (link in discussion).
[0] https://news.ycombinator.com/item?id=30808856
[1] https://www.redcrossblood.org/donate-blood/blood-donation-pr...