2. Blood test and bloodletting:[1]

It is forbidden to let blood on Erev Yom Tov of the last day of Sukkos, which is Hoshana Rabbah, starting from the night of Hoshana Raba.[2] This applies even to forms of bloodletting that do not release so much blood, known as Kep Zetzin.[3] [Thus, one is not to have a blood test done on Hoshana Rabbah, and is certainly to avoid giving a blood donation, or having other form of blood work done, unless it involves a case of danger.[4]]

[1] Admur 468:23; M”A 468:15; Darkei Moshe 468:3; Kol Bo 58 in name of Maharam

[2] The reason: It is forbidden to let blood on the day of Hoshana Raba being that is it is an actual Erev Yom Tov, being that Shemini Atzeres is its own Holiday regarding a number of matters. [Admur ibid; Darkei Moshe ibid; Kol Bo ibid] Furthermore, it is forbidden to let blood even the night before, on the night of Hoshana Raba being that Hoshanah Raba is a time of judgment. [Admur ibid; M”A ibid; See Michaber 664; Rosh Hashanah 4a]

[3] Admur 468:23; M”A 468:15 in name of Maharil

The reason: As Hoshana Raba is a day of judgement. [Admur ibid; M”A ibid]

[4] See Nitei Gavriel 8:3 regarding Erev Shavuos based on Admur 468:23