Lessons from a proficiency testing event for acid-fast microscopy

Objectives: To evaluate the routine performance and the technical parameter s of different acid-fast staining methods: Kinyoun, Ziehl-Neelsen (ZN), aur amine, and auramine-rhodamine. Design and participants: The performance of 167 laboratories was analyzed u sing prestained :Ind unstained slides. Setting: Laboratories holding New York State permits. Results: The results revealed that Kinyoun's cold carbol fuchsin method is inferior to both tile ZN and fluorochrome (auramine and/or auramine-rhodami ne) methods. Even though 91% of the participants used commercial staining k its, the study identified unexpected errors concerning the concentration of carbol fuchsin, time for staining and counterstaining, and the concentrati on of acid alcohol for decolorization, which may significantly influence th e sensitivity. Besides these findings, the present study showed that the ex amination of < 300 view fields may also decrease the sensitivity of acid-fa st microscopy, In addition, we found that the sensitivity and specificity o f the ZN and fluorochrome methods are comparable if the procedural standard s :Ire followed, Conclusions: The strict and ongoing quality control of the "simple to perfo rm" acid-fast microscopy and the immediate review of commercially available staining kits are necessary Because of the rapidity of the fluorochrome me thod, laboratories with large specimen numbers should use this technique. I n all other cases, the ZN method should he used. Moreover, all clinicians s hould be aware of the method of acid-fast microscopy used and the proficien cy of the laboratory in performing the assay.