Efficacy of repeat sputum examination in RNTCP

The guidelines of repeat sputum smear examination in initial smear negative patients (ISN), who also fail the antibiotic trial of three samples have been incorporated in the RNTCP diagnostic algorithm in India in 2005. This study was conducted to assess the utility of repeat sputum smear examination in symptomatic initial smear negative patients to detect new smear positives in the state of Delhi.

The monthly records of the laboratory abstracts for the six quarters for all the 24 districts of Delhi were analysed w.e.f. first of January 2006 to 30th June 2007.

A total of 243,244 TB suspects were examined for diagnosis during the six quarters w.e.f. January 2006. Of these, 37,666 were found positive on sputum smear microscopy giving a positivity rate of 15.4%. During the same period, a total of 2,195 (1% of ISN ) TB suspects underwent repeat sputum examination, of which 272 were found positive giving a mean positivity of 12.3%.

A significant number of apparently smear negative TB cases may in fact be smear positive due to various reasons and can be detected by a simple repeat sputum examination. Yield of sputum positive cases in sputum reexamination is almost the same as in initial sputum examination i.e. 10-15%. Therefore, the policy of repeat sputum examination in symptomatic initial sputum negative cases failing the antibiotic trial should be meticulously followed as advocated in the RNTCP diagnostic algorithm.