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Free Content Using likelihood ratios to estimate diagnostic accuracy of a novel multiplex nested PCR in extra-pulmonary tuberculosis

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SETTING: A tertiary care centre in Mumbai with a referral bias towards treatment failures.

OBJECTIVE: To standardise and evaluate a novel single tube multiplex nested polymerase chain reaction (PCR) targeting insertion sequence (IS) 6110, mpb64, rrs and rpoB genes for rapid diagnosis of extra-pulmonary tuberculosis (EPTB).

METHODS: The PCR assay was evaluated among 489 consecutive consenting patients, and results were compared against a composite reference standard comprising smear microscopy, culture, clinical symptoms, radiological scan and histology.

RESULTS: PCR assay reported a pooled sensitivity of 94.5% (242/256, 95%CI 91–97): 91.9% (125/136, 95%CI 86–96) for smear-negative composite reference standard (CRS) positive cases and 97.5% (117/120, 95%CI 93–99) for smear-positive CRS-positive cases. The PCR positivity rate increased from 91.7% (235/256, 95%CI 88–95) when presence of IS6110 was considered alone for reporting a test as positive to 94.5% (242/256, 95%CI 91–97) when used in combination with other three gene targets, with a specificity of 96.4% (212/220, 95%CI 93–98). A positive likelihood ratio of 26 (95%CI 13–51) and a negative likelihood ratio of 0.06 (95%CI 0.03–0.09) makes the test useful for ruling out and ruling in the disease.

CONCLUSION: Culture should not be replaced by PCR as a gold standard; however, PCR can be used as a rapid, accurate tool in the diagnosis of EPTB.
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Keywords: composite reference standard; extra-pulmonary tuberculosis; likelihood ratios; multiplex nested PCR; post-test probability

Document Type: Research Article

Affiliations: P. D. Hinduja National Hospital and Medical Research Centre, Mahim, Mumbai, India

Publication date: 2012-02-01

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  • The International Journal of Tuberculosis and Lung Disease publishes articles on all aspects of lung health, including public health-related issues such as training programmes, cost-benefit analysis, legislation, epidemiology, intervention studies and health systems research. The IJTLD is dedicated to the continuing education of physicians and health personnel and the dissemination of information on tuberculosis and lung health world-wide.

    Certain IJTLD articles are selected for translation into French, Spanish, Chinese or Russian. They are available on the Union website

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