Nested PCR in lung tissue for diagnosis of pulmonary tuberculosis.

Diagnosis of pulmonary tuberculosis (TB) is difficult in cases with an unusual presentation and often requires a lung biopsy. The goal of this study was to determine the clinical usefulness of nested PCR on lung tissue for the diagnosis of pulmonary TB. Clinical and laboratory data were reviewed from patients who underwent diagnostic lung biopsies, followed by nested TB PCR on formalin-fixed paraffin-embedded lung tissue specimens. The diagnostic yield and clinical impact of nested PCR were investigated. Of the 223 patients studied, 142 were diagnosed with TB. Microbiologically confirmed TB was identified in 71 patients. Compared to culture results, the sensitivity, specificity, positive predictive value and negative predictive value of nested PCR were 85%, 99%, 98% and 88%, respectively. Nested PCR was more sensitive than acid-fast bacilli smear of respiratory specimens and histopathological findings. The PCR results provided an early diagnosis and initiation of treatment for TB. However, negative PCR results did not lead to discontinuation of unnecessary TB treatment in patients on medication. In conclusion, nested PCR on lung tissue specimens is a useful diagnostic test for pulmonary TB in patients with an unusual presentation.