Evaluation of a two-reagent cold staining method for detection of acid-fast bacilli.

SETTING

Tuberculosis Research Centre, Chennai, India.

OBJECTIVE

To evaluate a two-reagent cold staining method for detection of acid-fast bacilli in sputum smears. SPUTUM SAMPLES: Two hundred and forty-four samples from pulmonary tuberculosis patients attending Tuberculosis Research Centre were used.

METHODS AND DESIGN

Two smears were prepared from each of the samples, of which one was allotted to the two-reagent cold staining method and the other to the Ziehl-Neelsen (Z-N) method. The smears were read blind by a single technician. To ensure correct grading, a senior technician checked all positives and 20% of the negative smears. All the samples were processed by modified Petroff's method for culture of Mycobacterium tuberculosis.

RESULTS

The concordance (smear grade one above and one below) between the methods was 90% (kappa value, 0.7). The performance of the cold method and the Z-N method was similar when their smear results were compared with culture results (cold method vs. culture, kappa = 0.61; ZN method vs. culture, kappa = 0.67)

CONCLUSION

The two-reagent cold staining method was found to be as sensitive and specific as the Z-N method. However, large-scale multicentric studies in different climatic conditions need to be conducted to assess its efficacy in the diagnosis of pulmonary tuberculosis.