I believe it is very important not to get these issues mixed up. I recently had a hlc member state that the reason for the allowance for fractions was because of the safer procedures being used today. I pointed out that while that is true, the JW reason for not taking blood has always been stated to be built on the sacredness of blood, not the health benefits, and thus the need to pour it out to be returned to Jehovah". It has never been a stance built on the issue of health, though that has often been cited as a side benefit.
True some individual JWs have used the "good health to you" at Acts 10:29 in their reasoning, and the society usually does not discourage it, but officially they have stated that that refers more to a sign off greeting that was used generally at that time.
Always remind them that this is an issue of sacredness, not health, according to the society. To make this a health issue is to give wiggle room.
Axelspeed