The backdrop against which the Apostolic Decree was spoken was a dispute that arose as to whether Gentile converts to Christianity should be circumcised and follow the Law.
The eating of blood as forbidden in the Law is therefore unquestionably the context in which the phrase, "Keep abstaining....from blood" was spoken. (The JW Bible dictionary, Insight On The Scriptures under the article "Paul" in fact explacitly states this.) Consequently, the MOST that any Witness can claim is that the Apostolic Decree forbade the EATING of blood. (Even this is debatable though, as some commentators are of the opinion that the Decree does not carry the force of command.)
As a result, the very LEAST required of the Witness adherent is a demonstration that transfusion is either a physical or moral equivalent to the eating of blood.
And here is where you can have a field day if you are familiar with the some very common logical fallacies, because Witnesses will literally try every trick in the book in defense of the transfusion taboo.
Some Witnesses will attempt a demonstration of equivalency through the use of false analogy: ("If a doctor forbade you to consume alcohol, could you inject it into your veins?") However blood is not a simple compount like alcohol. Blood is living tissue and a transfusion of blood is the transplant of living tissue. The Witnesses themselves recognize this distinction in all other transplant scenarios. The ludicrous nature of their analogy can easily be shown by comparison: "If a doctor forbade you to eat meat could you accept a kidney transplant?"
Some Witnesses will attempt to demonstrate equivalency through equivocation. They will use terms generic enough to apply to both the consumption of blood and the transfusion of blood, claiming that, "The Bible forbides TAKING IN blood."
This is another logical fallacy. Drinking a glass of water and drowning in a lake can both be described as "Taking in water." Does this make them physical equivalents? Marital sex and adultery both fall into the general catagory of Sex. Does this make them moral equivalents? Of course not. Equivalency cannot be established through generalization.
Other Witnesses will betray their lack of education through bad grammar: They will say, "The Bible says ABSTAIN from blood! Would you be ABSTAINING from blood if you accepted a transfusion?" However the incomplete predicate, "abstain from blood" cannot be invoked as an independant construction apart from the context that conpletes it without adding a transitive verb.
The reason for this is simple. There is no such thing as abstinance from a physical object. (Even though we may sometimes think and express ourselves in those terms.) For example, what would it mean if I said, "Abstain from paper." Without an additional verb, that statement is grammatically incomplete and means nothing. You can abstain from WRITING on paper or TEARING paper or even WASTING paper, but an abstinence from the physical object itself is meaningless. To reiterate, you don't abstain from objects, you abstain from acts done in connection with objects.
With that in mind, the unspoken verb inherent in the context of Acts 15:28, 29 is "eating" or possibly "drinking" (Compare the rendering in Moffat, TEV Phillips Modern English)
Still other Witnesses will claim in effect to know the Mind of God by asserting that what God really wanted to forbid was the USE of blood --something that the Bible doesn't actually state. They will usually attempt to support this assertion with an argument from silence, pointing out that God never authorized or otherwise sanctioned the use of blood. This is yet another logical fallacy, a form of hasty generalization where the complete lack of evidence is used to justify a conclusion. In this case there is nothing remarkable about the Bible's silence on matters alien to its historical context. The Witnesses themselves recognize the irrelavent nature of the Bible's silence in all other medical scenarios.
Regardless of what fallacious argument is advanced, the Witnesses can't get around the fact that Acts 15:28, 29 was a reference only to the consumption of blood as forbidden in the Law