Image caption How do doctors know if a patient is really dead?

Newspapers this week have reported a story about a woman who 'returned from the dead'. Tasleem Rafiq collapsed at home and was taken to hospital in an ambulance where doctors tried to resuscitate her for about 45 minutes without success.

Her family were told she was dead - but 11 hours later she 'woke up' when her daughter asked her a question, according to interviews.

Now and again stories like this crop up. In April it was reported that a Chinese woman climbed out of her own coffin six days after she was declared dead following a fall.

In 1996, Daphne Banks, a farmer's wife from Cambridgeshire, was pronounced dead at her home by a doctor after an attempted suicide overdose on New Year's Eve - only to be found alive in a hospital mortuary when undertakers spotted that she was still breathing.

Exceptionally rare

The Royal Berkshire Hospital in Reading, which treated Mrs Rafiq, said the clinical team was unable to detect a pulse because it was so faint - but she was breathing.

Identifying precisely when death has occurred can be difficult - especially in the heat of the moment Dr Kevin Fong, Consultant anaesthetist

Dr David Mossop, lead consultant in the emergency department, said resuscitation protocol had been followed correctly and after 45 minutes, with blood tests showing a profound lack of oxygen, he expected a severe amount of brain damage. But there was none. "That is very unusual," he said. He added that he had seen a similar case once before in his career.

This raises the question of how difficult can it be to diagnose death?

Medical experts are confident that misdiagnosis is exceptionally rare.

Dr Kevin Fong, a consultant anaesthetist who has investigated bringing patients back from the dead for a BBC Horizon documentary said: "Cases of 'coming back to life' after death has been wrongly diagnosed - are vanishingly rare.

"Death is a process rather than a moment in time - it is a process, a transition, life ebbs away slowly. Identifying precisely when it has occurred can be difficult - especially in the heat of the moment. But the diagnosis itself is based upon strict criteria which have to be adhered to."

In the UK there is no legal definition of death but there are guidelines for the diagnosis and confirmation of death to help when things are unclear.

Sir Peter Simpson, chair of the working group at the Academy of Medical Royal Colleges who put together the code, said: "If the guidelines are followed - they don't allow for misdiagnosis of death.

"The cases I have heard about of people 'coming back to life' are from abroad, where the criteria are less robust.

"Diagnosis of death has three parts: ask 'Why have they died', then diagnose death, and then wait for five minutes before confirming death."

The checklist for diagnosing death includes checking for a heartbeat and breathing, and examining the eyes to check if the pupils are large and unreactive.

Spontaneous rebeating

Sir Peter said: "If there is any doubt in the five minute wait, these checks should be done again.

"There are cases where the heart stops and restarts, this is called autoresuscitation, to my knowledge the maximum period this has happened for is 90 seconds."

Death checklist No spontaneous movement

No respiratory effort

No heart beat sound or palpable pulse

No reflexes

Pupils are fixed and dilated

Autoresuscitation, also known as Lazarus Syndrome, is very rare and not well understood.

In 2001, a paper in the Emergency Medical Journal identified more than 25 cases reported in scientific literature.

It takes its name from the Biblical story of Lazarus being raised from the dead by Jesus and is the spontaneous return of circulation after failed attempts at resuscitation.

It is thought to be the reason why the pulse of Michael Wilkinson, a roofer from Preston, returned 30 minutes after he was given the Last Rites in 2009. He was transferred to intensive care at Royal Preston Hospital and survived for two days before being pronounced dead a second time.

There are also a few circumstances which can muddy the waters. Sir Peter says: "We shouldn't be diagnosing death at all during these types of situations and when we first ask the question 'Why has this person died?' these factors need to be considered."

Frozen death

These include a low body temperature, if a patient that has taken drugs, for example sedatives or muscle relaxants, or those that have a medical disorder that alter the chemicals in their blood, like people with diabetes in a hypoglycaemic coma.

The implications of confirming a person dead are enormous, and hence doctors have an ethical obligation to ensure that they 'diagnose' death with due care and skill Dr Daniel Sokol, Medical ethicist

Sir Peter says: "When death is misdiagnosed it is often because these prerequisites have been forgotten. In these circumstances you have to wait until the effects have been reversed or the body returns to normal before diagnosing death."

This is illustrated in Dr Fong's BBC Horizon documentary which tells the story of Anna Bagenholm, a Norwegian skier, who 'returned from the dead' after being warmed back up to normal body temperature.

Out skiing in 1999 she fell into an icy river and became trapped under the ice for 80 minutes - her heart stopped beating. The freezing water caused her core temperature to drop more than 20 degrees below normal.

Once she was airlifted to hospital, doctors worked for nine hours to save her life - she was connected to a machine that warmed up her blood outside her body before it was fed back into her veins. As her body temperature began to reach normal, her heart began to beat.

Diagnosing death also comes with an ethical dimension - the guidelines say confirming death needs to be done without unnecessary and distressing delay.

Dr Daniel Sokol, a barrister and medical ethicist at Imperial College London, said: "The implications of confirming a person dead are enormous, and hence doctors have an ethical obligation to ensure that they 'diagnose' death with due care and skill.

"Factors such as lack of knowledge, inexperience, lack of time, fatigue, pressure from colleagues, and other factors can affect an individual doctor's clinical assessment. In difficult cases, a suitably experienced doctor should confirm the death, and second opinions can also reduce the risk of error."