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Evaluation of a two-reagent cold staining method for detection of acid-fast bacilli
N Selvakumar1, M Gomathi, F Rehman
1Tuberculosis Research Centre (ICMR), Chetput, Chennai, India. modeldots@vsnl.com
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.