The WT has said
*** w78 6/15 p. 30 Questions From Readers ***
? Would it be wrong to submit to a blood test?
Based on their knowledge of the Scriptures, most of Jehovah’s Witnesses, if not all, do not object to such tests. The small quantity of blood removed from the body is not eaten or injected into someone else. It is merely examined or tested before being disposed of.—Deut. 15:23.
If I were still a dub, I guess I would say that we are not in the business of splitting hairs over such small things, but you might argue that the principle is the same?? - as you may think??
As for employment ? if the blood is not to be transfused then I cannot see that they would have any objection.