title: How many sputum specimens are necessary to diagnose pulmonary tuberculosis?
abstract: The definitive diagnosis of pulmonary tuberculosis (PTB) relies on identifying or culturing Mycobacterium tuberculosis from respiratory specimens. National guidelines have recommended obtaining 3 sputum specimens from patients with suspected tuberculosis, but there has been little data on the number of specimens actually needed to support a diagnosis. We retrospectively reviewed all patients diagnosed with PTB at a public inner-city hospital and assessed the sensitivity of the acid-fast bacilli (AFB) smear and the number of smears needed to establish the diagnosis. Between January 1, 1997 and October 1, 2000, 425 patients were diagnosed with culture-proven PTB. Acid-fast bacilli (AFB) smears and cultures were performed on 951 respiratory specimens from 425 patients. The overall sensitivity of a positive AFB smear increased from 67% with 1 sputum collected to 71% and 72%, respectively, with the second and third specimens. The sensitivity of smears from 239 HIV-negative patients was 75%, 79%, and 80% with 1, 2, and 3 smears, respectively, collected compared with 57%, 61%, and 62%, respectively, for 142 HIV-positive patients. In summary, 2 respiratory specimens proved adequate in establishing a diagnosis of tuberculosis, and the third specimen added little additional diagnostic value.
authors.affiliation: Division of Infectious Diseases, Emory University School of Medicine, Atlanta, GA 30303, USA. mkleona@emory.edu
authors.forename: Michael K
authors.initials: MK
authors.lastname: Leonard
authors.forename: Dawn
authors.initials: D
authors.lastname: Osterholt
authors.forename: Ekaterina V
authors.initials: EV
authors.lastname: Kourbatova
authors.forename: Carlos
authors.initials: C
authors.lastname: Del Rio
authors.forename: Wayne
authors.initials: W
authors.lastname: Wang
authors.forename: Henry M
authors.initials: HM
authors.lastname: Blumberg
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013183:Sputum / Q000382:microbiology*; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis*