Why do Jehovah Witnesses not take blood?
A baptized Witness who unrepentantly accepts a blood transfusion is deemed to have disassociated himself from the group by abandoning its doctrines and is subsequently subject to organized shunning by other members.
Thus, Jehovah's Witnesses regularly refuse transfusions for themselves and their children because they believe the procedure creates a risk of losing eternal salvation.
1945
The church organisation, the Watchtower Society, introduced the policy on refusal of blood in 1945. Since 1961 the church has enforced it by “disfellowshipping” or expelling un-repentant members who wilfully accept prohibited blood components.
Last Offices are performed as normal, unless the family have special wishes. The body should be wrapped in a plain sheet. There is no religious prohibition against post-mortem, but most Jehovah Witnesses refuse them if there is no legal requirement. There is no religious prohibition against organ donation.