Concentration of sputum by cytocentrifugation for preparation of smears for detection of acid-fast bacilli does not increase sensitivity of the fluorochrome stain

Abstract

To evaluate the usefulness of cytocentrifugation for detection of acid-fast bacilli (AFB) in sputum specimens, we compared this method to a traditional concentration method for the preparation of smears. A total of 844 sputum specimens (from 579 patients) of adequate volume that were submitted for detection of mycobacteria were evaluated. A portion of each specimen was used for cytocentrifugation; the remainder was processed by our decontamination-concentration protocol (2% sodium hydroxide-N-acetyl-L-cysteine; centrifugation at 3,600 x g for 15 min) for preparation of smears and culture. All smears were stained with auramine O. Ninety-four cultures from 46 patients gave positive results, and AFB were seen in one or both smears from 53 specimens; 3 of the latter specimens (positive by both smear methods) were culture negative. Of the 50 AFB smear-positive and culture-positive specimens, 46 were smear positive by traditional concentration, and 47 were positive by the cytocentrifugation smear (P, not significant). Cultures of all specimens that were smear positive by only one method grew nontuberculous mycobacteria. The routine use of cytocentrifugation for concentrating sputum specimens increases the cost of smear preparation but does not increase detection of AFB by auramine O staining; however, it would be useful in handling emergent requests for AFB smears.