The entire WT prohibition on blood lays on one scripture... Acts 15:29. They try to bolster that prohibition by using the "principle" of the Mosiac Law regarding blood.
Now...forget all the shit about fractions and elements and blah blah blah...
JWs supposedly accept the Bible as the last word on any subject. Their entire theology is supposedly based on God's Word. They accept Jesus as God's son who fulfilled the Law Covenant and set up the Christian congregation. Jesus is ruling at God' right hand and is King.
If you accept that, then let Jesus, the King, God's son weigh on the matter. He didn't say anything about eating blood (or transfuing it) you say? No, not in so many words. What he did do was set the principle of how one views the sanctity of life. If the WTS can imply "principle" from the Law Covenant how much more fitting is it to apply "principle" from Jesus' words and actions?
Matthew 12: 1-13 (NWT)
1 At that season Jesus went through the grainfields on the sabbath. His disciples got hungry and started to pluck heads of grain and to eat. 2 At seeing this the Pharisees said to him: “Look! Your disciples are doing what it is not lawful to do on the sabbath.” 3 He said to them: “Have YOU not read what David did when he and the men with him got hungry? 4 How he entered into the house of God and they ate the loaves of presentation, something that it was not lawful for him to eat, nor for those with him, but for the priests only? 5 Or, have YOU not read in the Law that on the sabbaths the priests in the temple treat the sabbath as not sacred and continue guiltless? 6 But I tell YOU that something greater than the temple is here. 7 However, if YOU had understood what this means, ‘I want mercy, and not sacrifice,’ YOU would not have condemned the guiltless ones. 8 For Lord of the sabbath is what the Son of man is.”
9 After departing from that place he went into their synagogue; 10 and, look! a man with a withered hand! So they asked him, “Is it lawful to cure on the sabbath?” that they might get an accusation against him. 11 He said to them: “Who will be the man among YOU that has one sheep and, if this falls into a pit on the sabbath, will not get hold of it and lift it out? 12 All considered, of how much more worth is a man than a sheep! So it is lawful to do a fine thing on the sabbath.” 13 Then he said to the man: “Stretch out your hand.” And he stretched it out, and it was restored sound like the other hand.
Mark 2:23 - 3:5
23 Now it happened that he was proceeding through the grainfields on the sabbath, and his disciples started to make their way plucking the heads of grain. 24 So the Pharisees went saying to him: “Look here! Why are they doing on the sabbath what is not lawful?” 25 But he said to them: “Have YOU never once read what David did when he fell in need and got hungry, he and the men with him? 26 How he entered into the house of God, in the account about A·bi´a·thar the chief priest, and ate the loaves of presentation, which it is not lawful for anybody to eat except the priests, and he gave some also to the men who were with him?” 27 So he went on to say to them: “The sabbath came into existence for the sake of man, and not man for the sake of the sabbath; 28 hence the Son of man is Lord even of the sabbath.”
1 Once again he entered into a synagogue, and a man was there with a dried-up hand. 2 So they were watching him closely to see whether he would cure the man on the sabbath, in order that they might accuse him. 3 And he said to the man with the withered hand: “Get up [and come] to the center.” 4 Next he said to them: “Is it lawful on the sabbath to do a good deed or to do a bad deed, to save or to kill a soul?” But they kept silent. 5 And after looking around upon them with indignation, being thoroughly grieved at the insensibility of their hearts, he said to the man: “Stretch out your hand.” And he stretched it out, and his hand was restored.
Here Jesus set the principle that life was more important than the law. From reading how Jesus dealt with a situation that meant breaking a law in order to save a soul, the real question is:
Is it lawful to do a good deed or a bad deed, to save a soul or kill a soul, to allow a blood transfusion or to not allow a blood transfusion?