Equivalence of acid alone or acid-alcohol as decolourizing agent in Ziehl-Neelsen method.
BACKGROUND
Microscopists opine that acid-alcohol decolourized slides may enhance acid-fast bacilli (AFB) smear positivity, and published documents on equivalence of acid and acid-alcohol in ZN staining method are not easily accessible.


METHODS
National Institute for Research in Tuberculosis, Chennai, India.


OBJECTIVE
To document the equivalence of 25% sulphuric acid (ZN-acid method) and 3% hydrochloric acid-alcohol (ZN-alcohol method) as decolourizing agents in ZN method for detection of acid-fast bacilli.


METHODS
Two smears from each of 253 sputum samples from pulmonary tuberculosis patients, prepared and allocated, one to ZN-acid method and another to ZN-alcohol method were read blind. All the specimens were cultured for Mycobacterium tuberculosis by modified Petroff's method. Culture of M. tuberculosis was gold standard.


RESULTS
The concordance between the methods was 85% (kappa 0.68), and the sensitivity (79%) and specificity (89%) were same for both the methods.


CONCLUSIONS
In conclusion, the common belief that acid-alcohol decolourized slides give enhanced smear positivity stands void.
Department of Bacteriology (Retd), National Institute for Research in Tuberculosis (ICMR), Chetput, Chennai - 600 031, Tamil Nadu.
M Gomathi
MG
Sekar
Fathima
F
Rehman
Vanaja
V
Kumar
N
N
Selvakumar
D001431:Bacteriological Techniques / Q000379:methods*; D057886:Bleaching Agents; D004396:Coloring Agents; D000431:Ethanol; D006801:Humans; D009169:Mycobacterium tuberculosis; D012680:Sensitivity and Specificity; D013183:Sputum / Q000382:microbiology*; D013194:Staining and Labeling / Q000379:methods*; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000382:microbiology
D057886:Bleaching Agents; D004396:Coloring Agents; D000431:Ethanol