title: Hydrochloric vs. sulphuric acid in water for Ziehl-Neelsen staining of acid-fast bacilli.
abstract: METHODS
  Damien Foundation Bangladesh tuberculosis (TB) control projects.
  
  
  OBJECTIVE
  To compare 25% sulphuric acid in water (H(2)SO(4)) with hydrochloric acid in water (HCl) to differentiate acid-fast bacilli in sputum smears stained with 1% carbolfuchsin.
  
  
  METHODS
  For 1 year, all 158 microscopy laboratories used either H(2)SO(4) or 3%/6%/10% HCl for their routine work, alternating monthly between H(2)SO(4) and HCl. Each month a sample of five smears per laboratory was rechecked blind. After recording qualitative staining aspects, all sample smears were restained before rechecking, using H(2)SO(4) for destaining.
  
  
  RESULTS
  A total of 368,059 H(2)SO(4) and 335,436 HCl smears were routinely read, yielding 7.2% positive or scanty results in both groups. Of these, 9492 were rechecked. There was no difference in false-negatives detected (0.66%, 95%CI 0.44-0.95 for H(2)SO(4) vs. 0.68%, 95%CI 0.46-0.98 for HCl), but apparently there were more false-positives with H(2)SO(4) (2.12%, 95%CI 0.92-4.14 vs. 0.28%, 95%CI 0.00-1.54, P = 0.05). Qualitatively, only 3% HCl yielded significantly inferior differentiation results.
  
  
  CONCLUSIONS
  HCl 6-10% in water can be recommended for Ziehl-Neelsen destaining above H(2)SO(4). Diluting is easier and safer, and it may cause less confusion with false-positives during rechecking, including a restaining step.
authors.affiliation: Damien Foundation Bangladesh, Dhaka, Bangladesh.
authors.forename: K J M
authors.initials: KJ
authors.lastname: Aung
authors.forename: P
authors.initials: P
authors.lastname: Nandi
authors.forename: A
authors.initials: A
authors.lastname: Hamid Salim
authors.forename: A
authors.initials: A
authors.lastname: Hossain
authors.forename: A
authors.initials: A
authors.lastname: Van Deun
mesh_terms: D001459:Bangladesh; D004396:Coloring Agents; D005188:False Negative Reactions; D005189:False Positive Reactions; D006801:Humans; D006851:Hydrochloric Acid / Q000737:chemistry*; D012394:Rosaniline Dyes; D013183:Sputum / Q000382:microbiology; D013194:Staining and Labeling / Q000379:methods*; D013464:Sulfuric Acids / Q000737:chemistry*; D014376:Tuberculosis / Q000175:diagnosis* / Q000382:microbiology
chemical_list: D004396:Coloring Agents; D012394:Rosaniline Dyes; D013464:Sulfuric Acids; C006898:carbol-fuchsin solution; C033158:sulfuric acid; D006851:Hydrochloric Acid