[One who lets blood from his shoulders is required to wash his hands one time immediately afterwards.] If one does not wash his hands after letting blood from his shoulders, he will have inner fear for three days without knowing the source of the fear.
Must one wash his hands after getting a blood test or donating blood?
This is questionable. Practically it is best to wash hands.
If one touched blood is he required to wash his hands?
 4/19; This is due to the impure spirit which resides on the hand after bloodletting. This applies according to all Poskim. [See Halacha 2 in footnotes]
 Ketzos Hashulchan 2/11
 Kaf Hachaim 4/91; Peri Megadim 4 A”A 22; However see Piskeiy Teshuvos 4/27 which brings in name of Rav SZ”A that one is not required to wash hands.
 Piskeiy Teshuvos 4/27