I agree with the principle of life being sacred and therefore the use of blood, donated from a still living person, used to save someone's life is surely a conscience issue.
Watching John Cedars on YouTube the other night dissecting the shepherd book was also interesting concerning blood transfusions.
If you receive a transfusion and are repentant, then it seems you are 'all good', you will probably just be reproved.
This raises another question; in WT land, why is accepting a blood transfusion treated differently compared to the other sins listed in the OT? If you are unrepentant, you are disassociated instead of being disfellowshipped.