X-ray screening guidelines for tuberculosis need a makeover

December 1, 2009
H.A. Abella

Universal x-ray screening of tuberculosis has limited value, carries potentially adverse effects for patients, and creates an unnecessary cost burden, according to a study presented Monday at the 2009 RSNA meeting.

Universal x-ray screening of tuberculosis has limited value, carries potentially adverse effects for patients, and creates an unnecessary cost burden, according to a study presented Monday at the 2009 RSNA meeting.

Since most cases arise from reactivation of a dormant foci of infection, the treatment of latent tuberculosis represents a major component of the national strategy for wiping out the disease from the U.S. Thus, screening with the purified protein derivative (PPD) exam, also known as the Mantoux test, remains popular across the country.

For their parts, the American Thoracic Society and the Centers for Disease Control recommend that all PPD-positive individuals undergo routine chest radiography to exclude clinically active TB or to detect evidence of disease that would further increase risk of reactivation. However, findings from several small studies performed recently in the U.S. and abroad have found little radiographic evidence of active TB in this population, said lead investigator Dr. Ronald Eisenberg, an associate professor of radiology at Harvard.

Beginning in 2003, Eisenberg and coauthor Dr. Nira Pollock reviewed screening chest x-rays from PPD-positive individuals before their employment as healthcare workers. Using standard criteria, the investigators looked for signs of active or latent prior tuberculosis in the otherwise healthy subjects who were identified over the course of five years.

Even though abnormalities came up in the chest radiographs of 159, or about 6.1%, of 2586 PPD-positive individuals, researchers found no signs of active tuberculosis.

"The results of chest radiography did not clarify whom we should prioritize for prophylactic anti-TB treatment," Eisenberg said. "Of course, radiographic findings must be interpreted in context with the individual's exposure and medical history, so making the overall assessment of realistic reactivation risk is a significant challenge."

Nearly 60% of cases showed evidence of calcified granulomas, inflamed lymph nodes, or both. The rest came up with signs of pleural thickening (15.7%), fibrous scarring (10%), and noncalcified nodules (19.5%).

Such extremely low yield led researchers to conclude that the published guidelines for the interpretation of x-ray screening findings are inconsistent and out of date.

"Given the cumulative adverse effect and cost of chest radiography in current tuberculosis screening programs, these guidelines should be urgently revisited," Eisenberg said.