Accuracy and utility of commercially available amplification and serologictests for the diagnosis of minimal pulmonary tuberculosis

Diagnosis of patients with minimal active tuberculosis (TB) is difficult, a s there is no single test with high sensitivity and specificity. The yield and clinical utility of a combination of diagnostic tests were prospectivel y studied among 500 consecutive patients referred for sputum induction for diagnosis of possible active TB. Patients underwent sputum induction, chest X-ray, tuberculin testing, and had blood drawn for serologic testing (Dete ct-TB test; Biochem ImmunoSystems). Sputum was examined with fluorescent mi croscopy and PCR (Amplicor MTB-Roche) and cultured for mycobacteria using l iquid (BACTEC) and solid media. For the diagnosis of the 60 cases of active TB, sensitivity and specificity, respectively, of the following diagnostic tests were mycobacterial culture, 73% and 100%; PCR, 42% and 100%; chest X -ray, 67-77% and 66-76%; tuberculin testing, 94% and 20%; and serology, 33% and 87%. After consideration of PCR and radiographic and clinical characte ristics, a positive serologic test was independantly associated with diagno sis of active disease (adjusted odds of disease if positive, 2.6; 95% confi dence limits, 1.1,6.1). No currently available test has sensitivity and spe cificity high enough for the accurate diagnosis of minimal pulmonary TB. Ut ilization of a combination of tests, together with consideration of key cli nical characteristics, could improve diagnostic accuracy.