Dr Phillippa Poole switched on the light, saw her friend's deeply tanned face and realised she might have only hours to save his life.

The young New Zealand consultant was on holiday in America but her friend was too weak to attend the family gathering, so she visited him at his house.

He told her he got dizzy when he stood up, had stomach pains and had just had a colonoscopy for a bowel problem.

When she turned on the light for a better look, his unnaturally tanned skin shocked her into action.

Her friend had Addison's disease, a rare but dangerous shortage of adrenal hormone, and the secret condition which afflicted President John F. Kennedy. Patients need cortisol to replace the missing hormones and can die within hours if left untreated.

About the same time the family doctor rang to say the man's blood sodium had dropped to a critical level.

Poole knew the resistance she would face as an unknown New Zealand doctor walking into a US emergency room with an apparently off-the-wall diagnosis, but she had no choice.

"We screamed off to the hospital and were trying to persuade American physicians that this person had an Addisonian crisis and was life-threateningly unwell and he needed cortisol urgently. They finally listened to me and he got the cortisol and he's fine."

A mystery illness with puzzling symptoms, a doctor's flash of insight into the obscure cause, a mad dash to save the patient... it all sounds familiar to viewers of the medical drama House - with good reason.

Phillippa Poole is a general physician at Auckland City Hospital, which makes her the New Zealand equivalent of Dr Gregory House - without the bad leg and cranky attitude.

She diagnoses patients whose symptoms do not appear to match any particular illness and decides how to treat patients with known but difficult conditions, such as out-of-control diabetes.

Like many local doctors, Poole enjoys the TV series for its tightly plotted, generally medically accurate storylines although she cringes at the House team's treatment of their patients.

"They just go in and do the bone marrow transplant and the lung transplant," she says, laughing at a Sunday night episode.

"The patient seems to be not even part of that."

Poole is a slight 52-year-old woman, who makes eye contact and laughs easily. A general physician for 18 years, she is married with a 20-year-old daughter, lives in Devonport and enjoys tramping, orienteering and cycling in her spare time - "it keeps me sane".

Her uncle was a doctor and her brother Garth is a surgeon at Middlemore.

Until last year she ran Auckland University medical school's academic programme and is still in charge of medical education. She spends three quarters of her time as an academic, teaching medical students and as she puts it "thinking about how to teach them better".

The rest she works as a consultant at Auckland City Hospital, where most of the hundreds of patients she sees each year come either direct from GPs or the emergency department.

The detective work starts with the patient's medical history. Increasingly hospital doctors get electronic access to lab tests and GP records, which is helpful says Poole, but the best information comes from asking questions and listening to the answers.

"There's a saying in medicine - the patient will generally tell you what's wrong with them if you just listen well enough."

She spends an hour in clinics with each new patient, half of it just talking.

By the time she physically examines a patient, she has a fairly good idea what she thinks is wrong. The examination is partly to confirm that and to check for anything else she may have missed.

Then she reviews the initial tests, such as blood tests, ECG (electrocardiogram) and chest X-rays, and decides if any more are needed.

Unlike House, she says, she doesn't order lots of expensive and often unnecessary tests. She also has about 20 patients in her care at once, so she has to be careful how much time she spends on each case.

Otherwise the process is much the same as you see on TV. Doctors pull all the information together - medical history, physical examination, test results - and try to match it against a mental picture of how a person would look and behave with a certain disease. In medical jargon this is known as an "illness script".

Experienced physicians use it to cut through the book knowledge they learn at medical school and make sense of a confusing range of symptoms, some of which may turn out to be irrelevant.

The technique enabled Poole to realise instantly that her friend in America had Addison's disease, a diagnosis which had eluded several other doctors focused on the individual symptoms.

"He'd been under doctors' care there but they were multiple sub-specialists," says Poole.

"The dermatologist had been cutting off his moles when they were turning dark, the gastroenterologists had done the colonoscopy but nobody had put the whole piece together."

The flipside of this intuitive approach is that a diagnosis expert must also remain open to all other possible explanations. Usually a patient with vomiting and diarrhoea will have food poisoning but it might be bowel obstruction or appendicitis.

Chest pain could point to heart attack - but also to pulmonary embolism (a blood clot in the lung) or dissection of the aorta (the large artery which carries blood away from the heart to the body).

Poole tries to clear her mind of any previous diagnosis and start afresh, knowing that a miss could prove fatal. She watches especially for tuberculosis, HIV and meningitis, which can hide behind symptoms like weight loss or fever.

Some busy doctors grumble that the obvious answer is most often right. Doctors who waste time looking for obscure diseases are nicknamed "zebra chasers", based on the medical saying; "When you hear hoofbeats, think horses, not zebras."

But in his book How Doctors Think - which Poole recommends for both doctors and patients - American doctor and writer Jerome Groopman switches the animal metaphor to argue the opposite.

"A maxim that I heard repeatedly during my training was 'If it looks like a duck, walks like a duck and quacks like a duck, then guess what? It's a duck'. But it isn't always a duck."

One of Poole's New Zealand colleagues famously refused to accept the obvious explanation and played a vital part in solving a medical murder.

In January 2000 Dr Andrew Bowers of Dunedin received a frantic early morning phone call from the hospital's head of psychiatry Dr Colin Bouwer, telling him his wife Annette was dead.

Bouwer wanted him to sign the death certificate immediately but Bowers suspected poisoning. He was right - Bouwer had been slowly lowering his wife's blood sugar levels and injecting her with insulin to kill her. Bowers' insistence on a post-mortem led to the discovery of the drugs in Annette's body and Bouwer's conviction for murder.

Usually the missing clue is less dramatic but can still save a life. Poole remembers a middle-aged woman on her ward who became increasingly breathless.

For two weeks, the medical team watched the shadows spreading across her chest X-ray with alarm and tried to think of the right question.

Eventually the woman had to be taken to a respiratory ward, where a medical student tried a few more questions. She pulled some pills out of her locker and asked: "Are these important?"

The pills were urinary antibiotics, which can cause an allergic reaction in the lungs. Doctors had asked what she was taking but it's not unusual for patients taking several medications to forget the details.

Another woman came in with an epileptic seizure and a very low salt level in her blood. The doctors built her sodium count back up again but could not understand why it was so low in the first place.

It took about four months of repeat visits and questioning to discover she was drinking about eight bottles of water a day, which had dramatically diluted her salt level.

Poole is a great believer in old-fashioned listening and thinking as the answer to most medical riddles.

Occasionally she will run symptoms through a computer programme which uses complicated algorithms to predict likely diagnoses. But most programmes are not sophisticated enough to recognise the subtle variations between individual patients, especially when their symptoms are vague or complicated.

They tend to throw out lists of about a dozen possibilities, says Poole, which tend to distract you from the three or four which need most attention.

She also treats lab tests with caution. Doctors have access to an impressive range of technology when they search for a disease, including blood tests, X-rays, MRI (magnetic resonance imaging) scans and biopsies, which test tissue samples for diseases such as cancer. But tests can produce false positives (incorrectly finding the disease) and false negatives (missing the disease). They can also be unpleasant or even dangerous for the patient.

Increasingly these days she sees symptoms which don't seem to have a diagnosis. If the disease is not life-threatening, the best thing a doctor can do is wait, rather than rush in for the sake of doing something.

Poole says one of the hardest things for everyone to accept is that medicine is full of uncertainty and even the best doctors will sometimes be wrong. Hospitals review all cases of fatal misdiagnosis but it doesn't always lead to a solution.

"We'll never get to a 100 per cent diagnosis rate and nor should we, because that would mean we're doing far too many tests.

"The system just can't afford it and a lot of tests come with downsides."

Across the road at Auckland City Hospital, patients on the north-facing wards do the Herald crossword and look out at million-dollar views across the Waitemata Harbour.

Poole stands in the foreground for a photograph, rearranging the stethoscope around her neck. It's all she needs for most ward rounds, she says, along with a tuning fork, a reflex hammer and a healthy dose of experience.

"I tell my students; 'I've got the same tools you've got'," she says.

Then she taps her head and adds with a grin; "I've just got more up here."