The Acid-Fast Bacilli (AFB) Detection test using Ziehl-Neelsen (ZN) stain is a laboratory method used to identify acid-fast bacteria, primarily Mycobacterium tuberculosis, in clinical samples such as sputum, pus, or tissue specimens. The test relies on the ability of acid-fast organisms to retain carbol fuchsin dye even after treatment with acid-alcohol, which distinguishes them from non–acid-fast bacteria.