Hospital bosses have asked a High Court judge for permission to test an unconscious 12-year-old boy to find out if he is brain-dead.
Archie Battersbee, from Southend in Essex, has not regained consciousness since he was found at home on 7 April with a ligature over his head. His mother Hollie Dance thinks he may have been taking part in an online challenge.
Specialists treating the schoolboy at The Royal London Hospital in Whitechapel, east London, say brain death is "highly likely" and want a procedure carried out to check.
Archie's mother and father, Paul Battersbee, have raised their concerns about the proposal.
Hospital bosses asked a judge based in the Family Division of the High Court to decide what moves were in Archie's best interests.
Mrs Justice Arbuthnot considered the case at a private hearing in London on Thursday.
Fiona Paterson, for Barts Health NHS Trust, which runs the hospital, told the judge the "priority" is a decision on whether Archie should have the brain-stem test, which she said is "endorsed nationally" and would be done in a way that ensures any risk is "minimised".
Ms Paterson wants the judge to rule that the test is in Archie's best interests.
But Bruno Quintaville, for his parents, said they are "very concerned" that their son had not received treatment to relieve swelling on his brain.
"The concern is that he may be suffering every day more damage which could have been avoided," he said.
A campaign organisation called the Christian Legal Centre has been supporting Archie's family.
"We are standing with Archie and his family every step of the way," said the centre's chief executive, Andrea Williams. "We want to give him every chance of life."