Scriptural. Similarly, since the Scriptures are silent regarding blood fractions the Witnesses leave this up to one's personal choice and so our position on fractions is also completely Scriptural.
The Bible's requirements regarding blood and what parts are acceptable for Witnesses is NOT complicated. Even when modern medicine makes some in-depth reasoning necessary the principles are not complicated. We only have to ask ourselves the two questions: Is it "blood" and is it still part of my circulatory system?
However, if someone wants a direct and explicit Scripture statement on distinctions between blood parts they will not find it. This is, in fact, the reason Jehovah’s Witnesses do not "approve" nor "disapprove" any use of fractions. It has ALWAYS been clear that each individual must decide for themselves whether to use fractions.
The doctrinal position for all Christians is explicit in the bible: "Abstain from the use of blood." The Scriptures are clear that we must abstain from blood just as we avoid fornication and idolatry (Ac.15:20; 21:25).
In modern times Christians are confronted by scientific methods which can separate the fractional elements of blood. Since the Bible did not give us a direct command the Christian must use explicit biblical principles as well as implied principles from God's own actions in order to determine if these fractions are included in the blood prohibition (1 Jn 5:20).
The reason most JWs accept fractions is because they can morally and logically be viewed as no longer "blood." That this view is logical and scientific has been supported by several secular courts and medical experts who have legally defined "blood" as the four primary components and NOT any product below those.
Logically, as blood is broken down, at some point the components cease to be blood. If this logic was not correct then EVERY molecule which had ever been part of blood would still be considered blood and could not be ingested to eternity. Such a view would be unreasonable and completely illogical.
However, similar evidence excluding the primary components is completely lacking. Thus, there is absolutely no excuse for the use of any major components in transfusions.
Another reason most Witnesses accept blood fractions is because most of them are the product of destroying blood. The Bible's command is to destroy or "pour onto the ground" blood which has been removed from the body. In the case of most fractions the blood is essentially destroyed and will never be blood again. Therefore the Bible's mandate is carried out. Fractions are not blood when they are a product of destroying blood.
In the case of some larger fractions such as Cryosupernatant or Cryoprecipitate where the process does not necessarily completely destroy blood and may allow reconstitution other facts such as above are considered. Since God has allowed proteins such as found in Cryo to be transferred from the blood stream of mother to the fetus some individual JWs view this as an indication that Cryo is not included in the prohibition of blood. But, other Witnesses may refuse for various reasons such as the fact that some fractions "may be so similar to the function of the whole component and carry on such a life-sustaining role in the body."--w6/15/04; 23-24
Because the issue is a moral issue involving obedience to God, Witnesses make every reasonable effort to not disobey. So they follow the well known moral principle described as abiding by the "spirit of the Law" which is universally recognized as being logical and even binding. This principle does not stick to exactly what the Law explicitly states but applies it to unspecified circumstances.
As an organization, Witnesses have determined that the four primary components can still be viewed as "blood" on a moral and representational level. Each primary component individually can still represent basically what blood as a whole symbolizes: the life of the creature."
So deciding what is acceptable regarding blood is no more complicated than any other important moral decision in life.
*Saying "there were no transfusions in Biblical times so there can be no prohibition against blood transfusions" is like saying "there were no guns in Biblical times so there can be no prohibition against murder using a gun." Pretty ridiculous argument!
SOURCE: This is an answer provided by BAR_ANERGES to a question at Yahoo Answers.
Do Jehovah’s Witnesses accept any minor fractions of blood? (w04 6/15 pp. 29-31; Watchtower Online Library
Blood Fractions and Surgical Procedures (lv pp. 215-218; Watchtower Online Library)
Blood / Blood Transfusions - Links to Information (Defend Jehovah's Witnesses)
Why Do Jehovah's Witnesses Refuse Blood Transfusions? (Defend Jehovah's Witnesses)
Why Do Jehovah's Witnesses "Abstain From Blood"? (Defend Jehovah's Witnesses)
Is it Scripturally Acceptable for a Christian to Accept a Bone Marrow Transplant? (Defend Jehovah's Witnesses)
Do Jehovah's Witnesses Eat Red Meat Since it May Contain a Trace of Blood? (Defend Jehovah's Witnesses)
Articles, Websites and Videos Concerning Bloodless Surgery and Medicine (Defend Jehovah's Witnesses)