TB testing: today as good as 2-day

Oct 26 2012

Same-day sputum smear microscopy is as effective as standard smear microscopy for the detection of pulmonary tuberculosis, according to a review commissioned by the World Health Organization (WHO).

The findings support the WHO's 2010 statement that countries should consider same-day diagnosis over the previously standard 2-day testing.

Lucian Davis (University of California, San Francisco, USA) and colleagues say that their findings, "suggest that one of the key limitations of sputum smear microscopy as a tuberculosis case-finding technique, the requirement for repeated clinic visits, could be eliminated with no loss in diagnostic accuracy."

The authors included eight studies that enrolled 7771 patients with suspected tuberculosis in high prevalence countries, including Uganda, Ethiopia, Nepal, Nigeria, and Yemen.

They found that in studies that used Ziehl-Neelsen light microscopy, same-day testing for two smears had a sensitivity of 63% compared with 64% for standard testing for two smears, and a specificity of 98%, which was identical to standard testing.

The results were similar when the authors looked at studies using light-emitting diode fluorescence microscopy.

They also confirmed previous findings that performing three smears instead of two has little impact on sensitivity or specificity.

In an accompanying editorial, Daniela Kirwan (Imperial College London, UK) and Robert Gilman (John Hopkins University, Baltimore, Maryland, USA) say that Davis and colleagues' findings are controversial because specimens taken in the morning, precluded by the same-day approach, have been shown to have a greater bacillary load and higher sensitivity than spot samples.

They say that the review's finding that same-day testing is equally effective paves the way "for a major shift in the way tuberculosis programmes sequence sputum-smear examinations, and thus reduce rates of patient default and minimise delays in the start of treatment."

However, both they and the authors caution that measures to prevent the transmission of tuberculosis in clinics during the increased waiting time need to be implemented.

Writing in Lancet Infectious Diseases, Davis and colleagues say that a fast turnaround of testing, diagnosis and treatment will "realize the potential benefits of same-day strategies in sparing poor patients the costs of making several visits to health facilities, in increasing tuberculosis case detection, and in decreasing tuberculosis transmission in the community."

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