Hundreds of people may have been misdiagnosed with the sexually transmitted disease syphilis, according to health officials.
A study of five labs across the United States show approximately 18 percent of positive results from a test method used since the 1980s were in fact negative.
All pregnant women are given the test, as are people who are deemed at high-risk for sexually transmitted diseases.
People who test positive for syphilis are usually given penicillin, which can have side effects for some people.
It's not clear how widely used the problematic test is versus another method. The CDC recommends a second test when there's a positive result. Only about 14,000 Americans have the most contagious forms of syphilis.
The Associated Press contributed to this article.