A Jehovah's Witness with severe learning disabilities was able to receive blood if his life was at risk during surgery, a judge ruled.
The 28-year-old Belfast man's mother had opposed any required transfusions during dental surgery.
Her religion prohibits the acceptance of blood transfusions.
But Sir Declan Morgan said that in limited circumstances products could be given if they were to stop the man from dying.
The man, named only as GK and assessed as incapable of consenting to his own medical treatment, was due to have a number of teeth removed last week.
Blood products were to be made available to safeguard his life in the unlikely event of any severe bleeding during surgery.
But GK's mother, a practising Jehovah's Witness, refused to authorise their use.
No alternative
With clinicians unwilling to carry out the procedure unless blood was available if required, the case was brought before the High Court earlier this month.
Correspondence from a haemophilia nurse confirmed no alternative method of transfusion acceptable to Jehovah's Witnesses was available.
In a ruling delivered before the surgery on 20 August but only just published, Sir Declan set out the competing human rights issues involved.
As well the duty to protect GK's life, he pointed to the court's obligations to ensure no inhuman or degrading treatment, and the right to private and family life.
The case involved some of the most sensitive decisions judges have to make, he noted.
Sir Declan, Northern Ireland's most senior judge, identified his options as being either to make a declaration allowing blood use on the basis that otherwise GK would potentially die, or alternatively refuse to do so.
He said a therapeutic necessity could not be regarded as inhuman or degrading.
"I conclude that because of the risk to the life of GK in the very limited circumstances in which blood products could be used in this case that I should make a declaration to permit that to happen," Sir Declan confirmed.
"I want to make it clear that the declaration only permits the use of blood products in circumstances where it is necessary and that has been put to the court on the basis that it is necessary to ensure that GK's life is preserved.
"So those are the only circumstances in which blood products may be used on foot of this order."
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