Medical errors contribute to more than 250,000 deaths in the United States each year, according to a 2016 Johns Hopkins study. Other studies put the figure as high as 440,000.

But these mistakes are hard to track because death certificates rarely capture them, CNBC reports. The news outlet interviewed patient safety advocate John James, PhD, whose son collapsed and died while running at age 19 in 2002.

A few weeks earlier, James’ son had seen a cardiologist, who diagnosed him with a heart arrhythmia and sent him home with instructions not to drive for 24 hours.

"His death certificate said he died of a heart arrhythmia," he said, but my son really died as a result of "uninformed, careless, and unethical care by cardiologists.

“If you have a patient with heart arrhythmias of a certain level and low potassium, you need to replace the potassium, and they did not. And they didn't tell him he shouldn't go back to running."

The quarter-million deaths attributable to medical errors in the Johns Hopkins study would make these mistakes the third-leading cause of death in the U.S., behind heart disease and cancer. But it often goes unrecognized and isn’t listed among the Center for Disease Control and Prevention’s Top 10.

Martin Makary, MD, who led the study, said he considers death due to medical error as being caused by inadequately skilled staff, error in judgment or care, a system defect or a preventable adverse effect.

Read the full CNBC story below: