How common is misdiagnosis?
In the news this week has been the horrific case of Magdalena Malec, 31, who, despite showing all the classic signs of sepsis, went undiagnosed as she lay in a UK hospital recovering from an operation. Admitted following an ectopic pregnancy, Ms Malec had a raised temperature and a number of other red flags for sepsis, following her surgery. She later developed extensive limb ischaemia and eventually had to have both of her legs, her right arm and the fingers of her left hand amputated, and she also needed a kidney transplant.
“The catastrophic chain of events which led to Magdalena’s near death and horrendous injuries were completely avoidable if the hospital had followed its own sepsis protocol,” her lawyer said. The hospital has since apologised.
Cases like that of Magdalena Malec put a human face on the very real problem of diagnostic error. More publicity tends to surround cases of wrong-site surgery or drug errors, but the research shows that misdiagnosis is a far more common – and more intractable – issue.
One recent attempt at putting a figure to the problem found that patients were misdiagnosed around 10-15% of the time. And an Australian systematic review of diagnostic error in older patients found rates of over 10% for COPD, dementia, Parkinson’s, heart failure, stroke and MI.
But it’s not easy to nail down figures, as many hospitals and practices don’t keep count and there can be strong motivations for doctors not to report a wrong diagnosis. On top of that, misdiagnosed patients may also follow up with another doctor who makes the correct diagnosis, with the first doctor never realising their mistake.
There are various methods researchers use to try and quantify diagnostic error. The gold standard is said to be autopsy studies, which consistently identify diagnostic discrepancies in 10-20% of cases. Of course, not all deaths are subject to autopsy, and those that are may already be cases where the diagnosis is unclear.
Another, if subjective, method is patient surveys, which show that around a third of patients have been the subject of a misdiagnosis or have had a family member of close friend who has been misdiagnosed. ‘Secret shopper’ studies have also been carried out, where real or simulated patients with classic symptoms of a condition present to a doctor or hospital. In these studies, doctors misdiagnose the patient in around 13% of cases.
Second reviews offer yet another opportunity to quantify diagnostic error. These have shown that 10-30% of breast cancers are missed on mammography, and 1-2% of cancers overall are misread on biopsy samples.
Misdiagnosis and delayed diagnosis are also far and away the greatest cause of malpractice suits, which point to how common they are. Of course, not every misdiagnosis is actionable: under Australian law, diagnostic error is only considered negligent if it falls short of Australian medical standards and is the result of the doctor failing to take “reasonable care” in diagnosing the condition.
Misdiagnosis is “the hidden part of the iceberg of medical errors that dwarfs other kinds of mistakes,” says Dr David Newman-Toker of the Johns Hopkins School of Medicine, who has extensively studied the problem.
In a survey, the top reasons doctors gave for cancer misdiagnosis were “fragmented or missing information across medical information systems”, along with “inadequate diagnostic resources”. But Dr Newman-Toker says they more typically result from flawed ways of thinking, sometimes coupled with negligence.
He says drug errors and wrong-site surgery are not only less common but more amenable to solutions such as color-coded labelling or preoperative checklists. But there is no such easy or obvious fix for diagnostic error, he says.