The utility of immunohistochemistry for detecting mycobacterial infections in bronchoalveolar lavage & bronchial washings

BACKGROUND & OBJECTIVES: Tuberculosis, most commonly caused by Mycobacterium tuberculosis (MTB), is an infectious bacterial disease, with a major impact on global health. In this study, immunohistochemistry (IHC), acid-fast bacilli (AFB) culture and Ziehl-Neelsen (ZN) staining, techniques were compared on bronchoalveolar lavage (BAL) and bronchial washings (BW) with respect to sensitivity and specificity for detecting mycobacteria, taking culture as the gold standard. METHODS: Consecutive BAL and BW specimens were included in the study, over a period of one year for which AFB cultures were available. Samples with diagnosis other than inflammatory pathology such as malignancies or inadequate samples were excluded. A total of 203 BAL and BW specimens from patients with age ranging from 14 to 86 yr were analyzed for the presence of mycobacteria. The utility and efficacy of ZN stain and IHC in detecting mycobacteria was tested using AFB culture as a gold standard. RESULTS: Out of 203 cases, 10.3 per cent (n=21) were positive on AFB culture. Of these, 5.9 per cent (n=12) smears were positive for ZN stain, whereas IHC positivity was seen in 8.4 per cent (n=17) of the cases. ZN staining had a sensitivity of 57.1 per cent and a specificity of 100 per cent whereas, IHC had a sensitivity of 81 per cent and a specificity of 81.9 per cent. INTERPRETATION & CONCLUSIONS: Comparison with AFB culture (gold standard), IHC was found to be superior to ZN stain in terms of sensitivity, whereas ZN stain was found to be superior to IHC in terms of specificity. These findings therefore suggest that IHC may be a useful adjunct to ZN stain in the detection of mycobacteria in specimens from the respiratory tract.