Relative Value and Cost-Effectiveness of Culture and Special Stains in Fine Needle Aspirates of the Lung

Abstract

To define the role of microbiologic stains and culture in lung fine needle aspiration (FNA) specimens. All lung FNA specimens over a nine-year period, with results of both culture and microbiologic stains (Gram's, methenamine silver and acid fast) were reviewed and correlated with clinical information. Sixty-five cases were identified; 13 cases represented clinically significant infections (20%). Gram's stain identified 3 infections and had 1 false positive result, while culture identified 7 infections and had 9 false positive results. However, all false positive cultures represented easily identifiable contaminants, and eight of nine cases had no associated acute inflammation or necrosis. Aspergillus species were detected in four cases by Papanicolaou and silver stain, while culture was positive in only one case. Coccidioides immitis was detected by both Papanicolaou stain and culture in one case. A single case of Mycobacterium tuberculosis was identified by both culture and acid-fast stain. While culture appeared more cost-effective than Gram's stain for identifying bacteria, both Papanicolaou and methenamine silver stain were more cost-effective for identifying fungi. In lung FNA specimens, culture and special stains should be restricted to specimens with acute inflammation or necrosis. Gram's stain and fungal culture are insensitive and not cost-effective, and fungi are often identifiable with routine stains.