Sodium Hydroxide (4%) with Phenol Red is a reagent used in the digestion and decontamination of sputum samples prior to culture for mycobacteria. Most clinical specimens submitted for acid-fast bacilli isolation are contaminated with more quickly developing commensal microbial flora. Additionally, acid-fast bacilli may be retained in respiratory secretions and not released for culture until the material is liquefied. Respiratory specimens, such as sputum, contain mucin which may trap microorganisms. Decontamination and digestion of the mucous components kills contaminating normal flora and allows slower growing mycobacteria to grow. Timely neutralization prevents potential loss of mycobacteria caused by high pH levels of decontaminants, resulting in the preservation of more viable organisms. Phenol red is used to indicate changes in pH. BM1320 is recommended by the UK Standards for Microbiology Investigations as part of their decontamination/digestion protocol; it is generally used in conjunction with Sputum Neutralising Buffer without Phenol Red (BM1324).