Giving blood for medical reasons (blood testing, dna testing, allergy testing, glucose monitor testing, high iron counts, ect....) is a non issue within the JW cong.
Thou shalt not waste ones semen on the ground either but its necessary to test for a successful vasectomy. + 97.3% of JW males wank it regularly and 97.1% of the 97.3% of them do so without repercussion.
Just sayin...