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Misdiagnosis leads to most medical claims, US study finds

Logo for John Hopkins Medical School for your Expert Witness storyResearchers studying 25 years of medical malpractice claims in the US found that diagnostic errors accounted for the largest number of claims. Diagnostic errors also caused the most severe patient harm and attracted the highest compensation payments –amounted to $38.8bn between 1986 and 2010. The research was carried out by a team from the Johns Hopkins University School of Medicine in Baltimore, Maryland, and was published online by the journal BMJ Quality and Safety.

The leader of the research, Prof David E Newman-Toker MD PhD, said: "This is more evidence that diagnostic errors could easily be the biggest patient safety and medical malpractice problem in the United States. There's a lot more harm associated with diagnostic errors than we imagined."

While the new study looked only at a subset of claims – those that resulted in a compensation payout for malpractice – the researchers estimated the number of patients suffering significant, permanent injury or death as a result of misdiagnosis ranges from 80,000 to 160,000 in the US annually.

Diagnostic error, say the researchers, can be defined as a diagnosis that is missed, wrong or delayed, as detected by some subsequent definitive test or finding. The ensuing harm results from the delay or failure to treat a condition present when the working diagnosis was wrong or unknown or from treatment provided for a condition not actually present.

"Overall, diagnostic errors have been underappreciated and under-recognized because they're difficult to measure and keep track of, owing to the frequent gap between the time the error occurs and when it's detected," said Prof Newman-Toker. "These are frequent problems that have played second fiddle to medical and surgical errors, which are evident more immediately."

He said experts have often downplayed the scope of diagnostic errors: not because they were unaware of the problem, but "...because they were afraid to open up a can of worms they couldn't close."

He added: "Progress has been made confronting other types of patient harm, but there's probably not going to be a magic-bullet solution for diagnostic errors because they are more complex and diverse than other patient safety issues. We're going to need a lot more people focusing their efforts on this issue if we're going to successfully tackle it."

He also noted that, among malpractice claims, the number of lethal diagnostic errors was roughly the same as the number that resulted in permanent, severe harm to patients. That suggests that the public health impact of these types of mistakes is probably much greater than previously believed because prior estimates are based on autopsy data, so they only count deaths and not disability.

The human toll of mistaken diagnoses is likely much greater than his team's review showed, he said, because the data they used covers only cases with the most severe consequences of diagnostic error. There are many others that occur daily that result in costly patient inconvenience and suffering. One estimate suggests that, when patients see a doctor for a new problem, the average diagnostic error rate may be as high as 15%.

As with other kinds of medical errors, diagnostic mistakes won't succumb to a one-size-fits-all solution, Prof Newman-Toker added. For example, patients with severe dizziness are misdiagnosed with benign inner-ear conditions instead of stroke for a different set of reasons than an infection is missed due to misreading laboratory tests. Checklists may prevent misdiagnosis of some conditions, but not others.