Equivalence of acid alone or acid-alcohol as decolourizing agent in ziehl - neelsen method.


Sekar, M.G .; Rehman, F .; Kumar, V .; Selvakumar. N .


Indian Journal of Tuberculosis; 2012; 59; 219-223.


Summary: 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.


Setting : 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 (ZNalcohol 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.


Conclusion : In conclusion, the common belief that acid-alcohol decolourized slides give enhanced smear positivity stands void.


Keywords : AFB; Decolourizing agent; Mycobacterium tuberculosis; Ziehl-Neelsen





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