A comparative study of sensitivity of sputum microscopy by direct method versus sodium hypochlorite concentration method at RNTCP Centre

Kalpana Date


In revised national tuberculosis control program (RNTCP), microscopic examination of sputum for AFB plays an important role in the initial diagnosis of tuberculosis. Decontamination and liquefaction with by 5% sodium hypochlorite increases sensitivity and safety for handling specimen. In this prospective hospital based cross sectional analytical study, patients of all ages and either sex coming to RNTCP centre were included according to RNTCP criteria. From each patient, two samples of sputum were collected one spot and one morning. One set of smears was prepared by RNTCP guidelines and remaining samples were concentrated by using 5% NaOCl, followed by centrifugation and staining with ZN stain. Both set of smears were observed by two observers to remove observer’s bias. A total of 882 patients were included in the study with 577 (65%) males and 305 (35%) females. A total of 172(19.5%) patients were positive by RNTCP method whereas 201(22.79%) patients were positive by concentration method diagnosing 29 additional patients. This constitutes a rise of 3.29%. This constitute 16.86% rise in case detection over RNTCP method. There is a rise in smear positive cases after concentration with 5% sodium hypochlorite solution. The bleach method has advantage over routine  RNTCP method as it is simple, does not require any additional expertise, is safe, reagents are also affordable and easily available and could diagnose additional cases.


Keywords: Tuberculosis, Sodium hypochlorite, Sputum microscopy

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