- Question: [Tuesday, 14th Sivan, 5781]
I have read that it is forbidden to do bloodletting on Monday or Thursday due to some kind of danger being involved. My question is regarding getting a blood test or giving a blood donation and as to whether this too should be avoided on Mondays and Thursdays, or if it is allowed.
While certainly bloodletting [which is in any event no longer practiced today] is to be avoided on Mondays Tuesdays and Thursdays, in my opinion, a blood donation, and certainly a blood test, is allowed on any day of the week and the Talmudic limitation does not refer to these forms of blood removals.
Explanation: The Talmud states that due to reasons of danger one should not blood let on a Monday Tuesday or Thursday. On Monday and Thursday, one should not let blood being that on this day the heavenly tribunal sits in judgment and remembers one’s sins and therefore it is dangerous to do so. Likewise, on Tuesday one should not let blood being that on this day the constellation of Maadim shines. Now, while not all danger regulations recorded in the Talmud are applicable in today’s times, and have therefore been omitted from the Poskim, nevertheless, this Talmudic statement is recorded in the Alter Rebbe’s Shulchan Aruch, even though it is omitted by other Poskim. However, seemingly even according to the Talmud and Alter Rebbe this danger only applies when one releases a copious amount of blood as was done by bloodletting in which up to 40% of one’s blood volume was removed, and it was considered a serious medical condition that have to be properly supervising and dealt with. This is opposed to giving a blood donation in which case only about 8% of one’s blood is removed, and certainly cannot be completed to a blood test which removes around only 30 mL of blood. Now, although we find regarding Erev Shavuos that one should not do even a type of bloodletting that releases less blood than normal, and therefore the Poskim write that one should not have a blood test or donate blood on Shavuos, nonetheless, we cannot assume that the same applies here especially when Admur who recorded the above ruling regarding Erev Shavuos does not record it here regarding Mondays Tuesdays and Thursdays. Furthermore, as the Talmud itself establishes there, regarding these matters we follow the public custom and since the public is certainly not accustomed to avoiding blood tests and the like on Mondays Tuesdays and Thursdays, therefore there is no danger involved and it may be done.
Sources: See Shabbos 129b; Admur Shemiras Haguf Vihanefesh 5 and 468:22-23; Tzitz Eliezer 12:46