Comparison of Acid-Fast Stain and Auramine Rhodamine Fluorescent Smear on Bronchoalveolar Lavage Specimens Submitted for Cytologic Examination

Abstract

Abstract Objectives Testing of bronchoalveolar lavage specimens with acid-fast bacilli (AFB) stain is not routinely performed in many institutions. In 2017, we began performing AFB stain on all BAL specimens submitted for cytologic examination. Herein, we evaluate the diagnostic value of this test in comparison to the auramine rhodamine fluorescent stain performed in parallel by the microbiology laboratory for specimens also submitted for AFB culture. Methods We retrospectively reviewed all BAL specimens that were reported as culture positive for Mycobacteria spp. (n = 109) by our microbiology laboratory between 7/20/2017 and 12/30/2018. Of these, 84 (77.0%) specimens were concurrently submitted for cytologic examination and reviewed by a board-certified cytopathologist. Results Of the 84 culture-positive BAL specimens submitted for cytologic exam, only 2 cases were positive for acid-fast bacilli on cytologic examination with AFB stain, yielding a sensitivity of 2.38%. In comparison, 11 of those specimens were identified on auramine rhodamine fluorescent stain, yielding a sensitivity of 13.1%. Both cases identified by the AFB stain on cytology were also identified by auramine rhodamine stain in microbiology. These data indicate that AFB stain conducted in cytology is 81.2% less sensitive for detection of AFB when compared to auramine rhodamine stain. All cases identified on smear and AFB stain (n = 11) belonged to the Mycobacterium avium-intracellulare complex. Conclusion Our study results suggest that in a low-prevalence population, the use of AFB stain on BAL specimens sent for cytologic examination lacks sensitivity and is unnecessary if the same specimen is also sent for microbiologic culture and auramine rhodamine stain. The use of AFB stain on BAL specimens that were not sent for AFB culture is suboptimal but may identify AFB in specimens obtained from patients for whom mycobacterial infection is not in the differential and may be clinically insignificant.