Objective: To study the effects of modifications in the Ziehl-Neelsen staining procedure on predictive accuracy for acid fast bacilli in comparison to the conventional technique. Simplicity of procedure and reagent economy were the factors taken into consideration.
Design: Comparative evaluation between thick and thin air-dried smears stained conventionally and thick ethanol-fixed smears stained by the modified technique was done.
Results: Positive predictive accuracy of all the three smears, that is, thick air-dried, thin air-dried and thick ethanol-fixed, was 100%. Negative predictive accuracy for thick air-dried, thin air-dried and thick ethanol-fixed smears was 36.36%, 32.33% and 34.78%, respectively. Overall predictive accuracy was 66.67% for thick air-dried, 61.90% for thin air-dried and 64.29% for thick ethanol-fixed. These differences were found to be statistically insignificant.
Conclusion: The modified method offers an accuracy comparable to the conventional technique, is simpler and with improved reagent economy. It is of special importance to diagnostic facilities in rural set-ups.