The relative sensitivity of special stains and culture in open lung biopsies

The author compared the efficacy of Gram's, methenamine silver, and acid-fast stains on tissue sections to conventional culture methods in vitro for detecting infection in 110 open lung biopsies (99 inflammatory, 11 neoplastic). Twenty-one cases of clinically significant infection were found (19%). Gram's stain and culture had sensitivities of 100% and 80%, respectively. However, 21 of the cultures grew clinically irrelevant organisms and 2 Gram's stains originally were misinterpreted. In contrast, methenamine silver and acid--fast stains were significantly more sensitive (80% and 100%) than their corresponding cultures (20% and 50%) and no methenamine silver or acid-fast stains were misinterpreted. In addition, methenamine silver stain had a higher positive predictive value than culture (100% vs. 60%). In conclusion, both methenamine silver and acid-fast stains are more sensitive than culture for detecting significant pathogens from open lung biopsies. Gram's stain is as sensitive as bacterial culture but is often misinterpreted. Moreover, interpretation of bacterial cultures is complicated by the frequent growth of clinically insignificant organisms.