“You also ask why one can be dis-fellowshipped for taking a blood transfusion but not for taking blood fractions. While both may affect the life of an individual, the expression "life-sustaining" in connection with blood transfusions is synonymous with the idea of taking in food for nourishment. In this regard both whole blood and major components of it carry nutrients, oxygen, and other nourishment to the body. It is this aspect of taking in blood, that is, to provide nourishment that links blood transfusions with the Biblical prohibition. Note that "Questions From Readers" of the July 1, 1975, issue of The Watchtower stated: "The Bible specifically forbids the taking of blood to nourish the body.-Gen 9:4; Lev. 17:1-14; Acts 15:28, 29." The motive or reason for taking a serum is significantly different. It is not to feed the body, as would be the case if there was an eating of whole blood (or a major component thereof) by mouth or by having it transfused intravenously. Rather, the antibodies that have been separated out are administered for the purpose of immunizing the body against a certain disease. While blood fractions in certain situations can be lifesaving, they do not operate to feed and nourish the body and in this way sustain life but, rather, utilize other mechanisms.” (Watchtower Branch letter of March 23, 1998 to Randall Jensen.)
But the Watchtower Society had known since the 1950s that transfusing blood is far different from eating blood for nourishment, that transfused blood is not digested but retained in the body much like a transplanted organ. “Transfused blood cannot be used by your body as food any more so than can a transplanted heart or kidney.” – (Watchtower 9/15/58, p. 575)
“By your words you will be condemned.” (Matthew 12:37)
http://ajwrb.org/do-jehovahs-witnesses-really-abstain-from-blood