I was asked to donate platelets this week because the local blood center is looking specifically for my blood type. The only practical time for me is over chol hamo'ed (as I am off from work). I have heard conflicting statements about whether it would be permissible to donate on chol hamo'ed. One side says that we avoid certain melachot on chol hamo'ed, including donating. I was told that the tzorech gufo, needs of my body, in this case, are not emergent or imminently time sensitive and I could schedule the donation for another time. But then I read a quote from the MDA in Israel,
"In addition, MDA calls on the public to donate blood during Chol Hamoed, due to the expected decline in blood donations during the holiday period."
My shul's rabbi drew a distinction between the potential for a real shortage of blood in Israel over chol hamo'ed and the less severe concern in the U.S. but I am still wondering about the pre-emptive nature of the Israeli call vs. the "we are, right now, looking for your blood type" phone call I got.
The "Physical need" category applies (it seems) only to the self, not to what I could do to address the physical needs of another person so I need an algorithm by which to determine if other cases qualify as acceptable on Chol Hamo'ed or not. Said algorithm would have to take into account a variety of questions such as
-->Would there be any difference if I could (or would) not donate any other time?
-->Does it matter if the blood bank claims that there "might" be a specific recipient or an expected need? Must they provide proof?
-->If the need was determined to be strong enough to be allowed on Chol Hamo'ed (a tzorech but not immediate piku'ach nefesh) would it be strong enough to push aside the practice of not eating Kitniyot (note -- this is a real and practical question)?