Heart data from elite basketball players show that a surprising amount have abnormalities — but these results are likely false positives that don't take into account how the heart changes during training, say researchers who analyzed data from hundreds of National Basketball Association players.

Training for a sport at an elite level changes the heart, so a chart of the heart’s electrical activity, called an electrocardiogram (or ECG) for an athlete will be different than one for a non-athlete. As a result, it can be difficult to discern whether someone’s ECG looks different because of training or because there’s an underlying disorder that might be dangerous. For a study published today in the Journal of the American Medical Association, scientists analyzed heart data from 519 NBA athletes. The results showed that using the most recent set of athlete-specific criteria, 81 had abnormal results even though the players were healthy.

The NBA requires each athlete to have their heart tested each year before the season begins. The evaluation includes an ECG, and a more sophisticated procedure called an echocardiogram. Echocardiograms use sound waves to create a visual image of the heart so doctors can see the size and shape and how blood flows through it.

Today’s study used test results for athletes who had played during the 2013 to 2015 seasons. Of these, 80 percent were black and most of the remaining players were white, and the average age was 25. The scientists analyzed the data using three specific sports-related criteria that are supposed to separate out what’s normal for athletes versus what’s not. Though 81 athletes have abnormalities using 2017 criteria, the numbers were higher using criteria from previous years: 108 using 2014 guidelines, and 131 using 2012 guidelines.

“When we compare the ECG data with matched echocardiographic data, we see that their hearts are actually normal and these abnormal ECGs are false-positive ECGs,” study author David Engel, a Columbia University cardiologist, told TCTMD. (They found no cases of structural heart disease.)

This means there are fewer and fewer cases of false positives from ECG under the new guidelines, but it’s still not perfect, and there still needs to be research into other types of diagnostic criteria, especially in light of heart-related NBA deaths.

The authors also write that the ECG data suggest NBA players have more heart abnormalities compared to other athletes, and this may be because the average age is older. There are limitations to the study, too. We don’t have a full set of physiological data that might be helpful, such as blood pressure; we don’t know what the underlying exact cause of the changes might be; and we shouldn’t generalize this to other sports. The results suggest that ECG criteria may need to be individualized for sport and that tore research should be done to find out better diagnostic methods.

Correction 12/7/17, 2017 9:23 a.m. EST: An earlier version of this post did not clarify that the heart abnormalities were likely false positives.