Optimisation of acid fast smears for the direct detection of mycobacteria in clinical samples.
OBJECTIVE
Despite its long history, the acid fast smear remains unstandardised. Technical variations in both the preparation of clinical material and subsequent staining mean that smear sensitivity relative to culture may vary from 50% to over 80%. This study assessed the sensitivity of acid fast microscopy at each of five stages of sample preparation and by both commonly used staining methods.


METHODS
Sputum samples thought for varying reasons to be highly likely to be culture positive were used to prepare a series of smears in which the effects of digestion (liquefaction), concentration (centrifugation), and decontamination (sodium hydroxide) could be assessed, together with a comparison of staining by the auramine/phenol and Ziehl-Neelsen techniques.


RESULTS
The most effective method for the demonstration of acid fast organisms in sputum was found to be an auramine phenol stain applied to a liquefied, concentrated sample and examined before the decontamination process.


CONCLUSIONS
The auramine phenol stain applied to a liquefied, concentrated sample and examined before the decontamination process is the most effective method for the demonstration of acid fast organisms in sputum.
Murray
S J
SJ
Regional Centre for Mycobacteriology, Public Health Laboratory, Institute of Pathology, Newcastle General Hospital, Westgate Road, Newcastle upon Tyne NE4 6BE, UK.
Barrett
A
A
Magee
J G
JG
Freeman
R
R
D001431:Bacteriological Techniques; D001576:Benzophenoneidum; D016009:Chi-Square Distribution; D004396:Coloring Agents; D006801:Humans; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification*; D013183:Sputum / Q000382:microbiology*; D013194:Staining and Labeling
D004396:Coloring Agents; D001576:Benzophenoneidum