A crucial link in WT's teaching that the Scriptures forbid blood transfusions is the argument that a transfusion is nothing more than eating, but by a different route. One of their favorite illustrations is if a doctor were to tell you to abstain from alcohol, could you then have an alcohol transfusion instead?
This appears persuasive until you turn it around: if a doctor were to tell you you needed a blood transfusion, could you drink it instead? Obviously not, because the blood would be digested in the gut, some nutrients would be absorbed into the bloodstream but the solids would be expelled with the rest of your solid waste. But drinking a pint of blood will do nothing to stop your veins collapsing if your circulatory system is hemorraging. It's about as sensible as, when your doctor tells you you need a kidney transplant, asking if you could just have some steak and kidney pie instead.