Evaluation of mycobacteriology laboratories: the acid-fast smear.

In a proficiency testing program, slides bearing acid-fast bacilli were sent to laboratories in New York State. The most reliable results were obtained in laboratories using the Ziehl-Neelsen method. Cold staining procedures were less reliable. The auramine-rhodamine fluorescent stain, which produced many false positives, should be confirmed by the Ziehl-Neelsen procedure. The testing program described can be used to determine whether laboratories perform the acid-fast stain effectively.