How often do medical misdiagnoses occur? Here's the data

An outspoken advocate for patients with multiple sclerosis just revealed she didn't have the chronic condition after all.

Actress Christina Applegate says doctors misdiagnosed her years ago. How often do errors like that happen, and how can they be prevented? 

There have been several studies into this problem with sobering findings.

One of the more recent ones came from the medical journal BMJ Quality and Safety.

It found 1 in every 14 hospital patients who are there for a general medicine reason receive a harmful diagnostic error.

Some people, however, might go to urgent care or a specialist to diagnose their sickness or condition. BMJ did a study on these cases as well, and released its findings back in 2014.

It found 12 million adults who seek outpatient care get a medical misdiagnosis each year. At the time, that was about 1 in 20 adults

It's also estimated that nearly 800,000 Americans per year die or become permanently disabled as a result of a misdiagnosis.

The physical impact is clear, but there's also an emotional toll. In her podcast, Applegate describes feeling lost after being told she doesn't have multiple sclerosis.

"This may come as great news but to me, it comes as very, like I'm back at square one," she said.

There are several reasons why a medical misdiagnosis happens. It could be a doctor misinterpreting test results, or problems when ordering diagnostic tests.

On the other side, patients might not provide an accurate medical history or description of their symptoms.

So, how can this be prevented?

For patients, doctors say to explain your medical history in a clear, chronological way, including family history. They encourage people to detail every symptom, even if they seem minor or unrelated.

And follow up on your test results rather than assuming no news is good news.

The conditions with the highest likelihood of a misdiagnosis include cancers and vascular events like a heart attack and infections.