Doctors says that cases of an incorrect diagnosis are rare
Doctors are being given tips to help them diagnose when someone is dead.
Although a patient coming back from the dead is rare, there is enough ambiguity in diagnosing death that doctors need guidance, experts have decided.
Rapid advances in life support, where machines take over the breathing of the moribund, have complicated the diagnosis, for example.
The Academy of Medical Royal Colleges' UK guidelines cover situations like hypothermia and drug-induced coma.
Back from the dead
There have been instances when people exposed to extreme cold have been presumed dead but have later shown signs of life again when their core body temperature has risen again.
Sedative drugs can also make a person appear to be dead when they are not.
The report's author, anaesthetist Sir Peter Simpson, said diagnosing death could be difficult.
"There are issues when people die in unusual circumstances with unusual sedative drugs on board or other extraneous things like low body temperature when it is inappropriate to confirm death.
"This new guidance for the first time clearly spells out when it is appropriate to diagnose death.
"Diagnosing death in whatever circumstances is a sensitive issue, which comes at a very distressing time for everyone.
"We hope that the detailed way in which the working party has addressed the issues will give help and confidence to all concerned."
The guidelines say the definition of death should be regarded as the irreversible loss of the capacity for consciousness, combined with irreversible loss of the capacity to breathe.
They replace existing guidance on brain death and include new advice on cardiac death.
The authors also decided it was important to separate completely the diagnosis and confirmation of death from anything to do with the issues surrounding organ donation and transplantation.
This was to avoid any concern that the diagnosis is influenced by the desperate need for life-saving donor organs which are in short supply.
Professor Dame Carol Black, chair of the Academy of Medical Royal Colleges, said: "I am confident that by addressing the ambiguities of the old Code, together with issues that have arisen as a result of new areas of clinical practice and the law, this new guidance will help both medical and nursing staff and equally our patients feel confident in the diagnosis and confirmation of death and its consequences."