Normal chest radiography in pulmonary tuberculosis: implications for obtaining respiratory specimen cultures.

Setting: Urban tuberculosis (TB) clinic, Nashville, Tennessee, USA.
Objective: Chest radiographs (CXRs) help in the diagnosis of pulmonary TB, but may be normal. Mycobacterium tuberculosis in culture is diagnostic of TB, but cultures are not routinely obtained in resource-poor settings. We examined rates and risk factors for pulmonary TB associated with normal CXR.
Design: An observational cohort study was performed among all respiratory culture-positive TB cases referred to the Nashville Health Department from October 1992 to July 2003. Clinical factors, demographics and underlying medical conditions were assessed.
Results: Of 601 study patients, 53 (9%) had normal CXRs: 31/138 (22%) were human immunodeficiency virus (HIV) infected and 22/463 (5%) were non-HIV-infected/unknown (P<0.001). Among HIV-infected patients, normal CXR was more likely in persons with renal failure (13% vs. 3%, P=0.048). Among non-HIV-infected/unknown patients, normal CXR was more likely in those who were asymptomatic at presentation (32% vs. 13%, P=0.022). In multivariable logistic regression analysis, HIV infection was associated with an increased risk of normal CXR (odds ratio [OR] 6.61, P<0.0001); factors associated with reduced risk were dyspnea (OR 0.24, P=0.026), positive sputum smear (OR 0.45, P=0.028) and cough (OR 0.48, P=0.038).
Conclusions: The rate of normal CXR among persons with culture-confirmed pulmonary TB was high. Respiratory specimen cultures should be obtained in TB suspects with a normal CXR, particularly HIV-infected persons.