WEDNESDAY, July 7 (HealthDay News) -- The lung function tests used to diagnose conditions like asthma may need to be adjusted to account for differences in patients' genetic ancestry, a new study suggests.

Now, physicians adjust the test results to account for factors like age, sex, race and weight, but not for mixed ancestry.

The study, published online July 7 in the New England Journal of Medicine, indicates more adjustments may be necessary because many people have mixed ancestry, which influences the test results.

"People throughout the world have a richer genetic heritage than can be captured by our current definitions of race," said study senior author Dr. Esteban G. Burchard in a journal news release.

"When we force patients into an individual box, such as 'African-American' or 'Caucasian,' we're missing a lot of genetic information," added Burchard, director of the University of California, San Francisco's Center for Genes, Environment and Health.

In the study, which looked at data from more than 3,000 patients, the researchers found that genetic ancestry significantly affects performance on the lung function tests.

The breathing tests can detect signs of illness like asthma and chronic obstructive pulmonary disease. Test results can also help doctors make decisions about disability claims and eligibility for lung transplants.

"Taking genetic ancestry into account could result in more appropriate treatment for patients," said study lead author Dr. Rajesh Kumar, an associate professor at Northwestern University Feinberg School of Medicine, in the release.

In an interview, Mayo Clinic pulmonologist Dr. Paul D. Scanlon said the study findings offer "a step forward in our understanding."

Blacks generally score lower on the tests than whites, added Scanlon, who wrote a commentary accompanying the new study. If test results aren't adjusted to account for this fact, patients may be wrongly diagnosed with lung disease because their test results appear too low.

Right now, the tests are a "very crude tool" because the benchmarks aren't designed to account for someone of mixed race like President Obama, he said.

More information

For more on lung function tests, see the U.S. National Library of Medicine.