The Ziehl–Neelsen stain is a differential staining method that identifies acid-fast bacilli (AFB).

Acid-fast organisms resist decolorization by acid-alcohol due to the high lipid content (mycolic acid) in their cell walls.

Clinical uses include:

Detecting tuberculosis (TB) and other mycobacterial infections.

Identifying Nocardia species (partially acid-fast).

Supporting diagnosis of pulmonary and extrapulmonary TB.

The test is performed on sputum, tissue, or other clinical samples.

Analyte: Acid-fast bacilli (AFB) such as Mycobacterium tuberculosis.

Normal Result: No AFB detected (negative).

Positive Result: Red/pink bacilli visible against a blue background → indicates presence of AFB.

Clinical Use:

Confirms suspected TB infection.

Helps differentiate mycobacterial infections from other bacterial diseases.

Guides further culture and molecular testing for definitive diagnosis.