A family health history is one of the most important things a patient can provide to a doctor.

This information can shed light on genetic, environmental and behavioral factors that influence the risk of some serious illnesses.

And you’d expect patients to know if any of their relatives had suffered from diseases such as cancer.

But a study published recently in the Journal of the National Cancer Institute suggests that expectation is wrong.

In the study, researchers focused on the four cancers most common in U-S adults… lung, breast, prostate and colorectal.

They interviewed more than one-thousand people, who provided information on cancer diagnoses in more than twenty-thousand relatives.

Then, researchers checked official records for about twenty-six-hundred of those relatives. They used databases including state tumor registries and Medicare claims records.

It turned out the percentage of patient-reported cancer cases that were confirmed ranged from a low of twenty-seven percent for colorectal cancer to a high of sixty-one percent for breast cancer.

The patients reported many cases the researchers couldn’t confirm.

There were also false negatives, where official records showed a cancer diagnosis but the patient said there was none.

Overall, the accuracy of the information from patients was low to moderate.

So, primary-care physicians should take note: Asking patients for a family health history is worthwhile, but the inquiry shouldn’t end there.

Human memory is fallible, and people don’t always disclose their health problems to relatives.

Encouraging patients to complete a formal health history using tools such as the Surgeon General’s web-based Family Health History could improve accuracy. But to ensure the best possible care, physicians should verify word-of-mouth information with cold, hard facts from objective sources.