There could be "100 reasons" for a doctor making a wrong diagnosis, and seeking a second opinion is critical to optimising treatment, a world-leading expert on patient safety says.
Most patients accept the first diagnosis they receive, but a range of studies suggest that diagnostic errors occur regularly.
A study by the Mayo Clinic found 88 per cent of patients received a new or refined diagnosis when they sought a second medical opinion.
Published in the Journal of Evaluation in Clinical Practice, only 12 per cent of patients had their original diagnosis confirmed.
Access to a second opinion can provide better accuracy, faster recovery and reduce waste in the health system, medical experts attending the first Australasian Diagnostic Error in Medicine Conference Melbourne have been told.
Professor Emeritus of Medicine Dr Mark Graber, President of the Society to Improve Diagnosis in Medicine, says fresh eyes catch mistakes and a second opinion could save a patient's life.
"It's a safety net to get a second opinion," he said.
"You never really know whether circumstances were ideal the first time around; maybe the doctor didn't have enough time, maybe they didn't have enough information, maybe they were distracted," Dr Graber said.
"Diagnosis can be a challenge when you consider there are 10,000 diseases but only 200 to 300 symptoms. If you are given a diagnosis with serious treatment implications or you're not responding the way you should to medication, a second opinion could save your life.
"Being open to a second opinion is a relatively easy and cost-effective path to a more accurate diagnosis."
Second opinion services, such as Best Doctors, are becoming available in Australia and private health insurers have started offering them to policy-holders.
However there are barriers to seeking a second opinion including financial reasons.
Dr Graber acknowledges many people can't afford to see another specialist for further advice.
"Many patients also feel awkward seeking a second opinion, they're worried that it conveys doubt in the person they're seeing to begin with," he said.
Director of Internal Medicine and Clinical Epidemiology at the Princess Alexandra Hospital, Associate Professor Ian Scott has argued that most clinical errors are not due to incompetence or inadequate knowledge but to the "frailty of human thinking" when dealing with complex conditions under time pressures.
He acknowledges the importance of a second opinion and says specialists themselves commonly seek advice from their peers.
"I think it is important where there is a condition of uncertainty about what the diagnosis might be or how best to investigate someone who has an undifferentiated clinical syndrome - I think it can be very useful to gain a second opinion," he said.