Leaders of Jehovah’s Witnesses are modifying their prohibition on receiving blood transfusions on religious grounds, now allowing members to decide whether to allow their own blood to be drawn and stored in advance for such things as a scheduled surgery with a risk of significant blood loss.

But the organization is retaining its wider prohibition against receiving transfusions of others’ blood — a procedure routinely used with patients after accidents, violence or other blood loss.

This long-held prohibition is one of the most distinctive and controversial teachings of the movement, which is headquartered in New York state and well-known for its assertive public proselytizing.

Jehovah’s Witnesses, who emerged in 19th century America, share many Christian beliefs but diverge from most other churches on key theological issues, such as the nature of Jesus and biblical prophecy. They are almost alone in their beliefs about blood transfusions.

The Governing Body of Jehovah’s Witnesses announced what it called a “clarification” of its teaching on Friday, saying it came after extensive prayer and consideration.

“Each Christian must decide for himself how his own blood will be used in all medical and surgical care,” Governing Body member Gerrit Lösch said in a video statement posted Friday on the denomination’s website.

“This includes whether to allow his own blood to be removed, stored, and then given back to him. What does this mean? Some Christians may decide that they would allow their blood to be stored and then be given back to them, others may object.”