This article waslast modified on 11 February 2018.

In December 2010 the World Health Organization (WHO) published an Expert Factsheet endorsing the rapid automated DNA test for TB in sputum (phlegm) that we wrote about here last September. However, there had been no studies in children.

On 18 July 2011 the journal Lancet Infectious Diseases published online a report of the accuracy of the DNA test (Xpert MTB/RIF) for the diagnosis of TB of the lung in children who had been admitted to hospital in Cape Town, South Africa with suspected TB between early 2009 and late 2010. The investigation was funded by the National Institutes for Health, the National Health Laboratory Service Research Trust, the Medical Research Council of South Africa and the Wellcome Trust.

The children were all less than 15 years old, half of them less than 20 months old. They had had either a cough for more than 14 days, household contact with TB, failure to gain weight, a positive TB skin test or a suspicious chest X-ray. Sputum (phlegm) for testing was ‘induced’ by the breathing of a very fine spray of salt solution for 15 minutes followed by physiotherapy and coughing, or suction if necessary.

The DNA test results were compared with the microscope examination of sputum smears and with sputum cultures as the “gold standard”. Of the 385 children who had all three tests on two sputum specimens, 58 had a positive culture. Smear testing detected 22 (38%) of these while the DNA test detected 44 (76%). Smears gave negative results in all 327 children with negative cultures while the DNA test gave 323 (99%) negative results.

The researchers concluded that, while the DNA test detection rate in children (76%) was significantly lower than that previously found in adults (98%), the test was twice as sensitive as the smear test that is widely used for screening in countries with a high prevalence of TB. They considered that the rapid DNA test on two induced sputum specimens is warranted as the first-line diagnostic test in children with suspected pulmonary tuberculosis to facilitate early treatment.

Postscript

WHO has expressed concern in a Policy Statement (11 July 2011) about commercial TB antibody tests currently sold to diagnose this important disease. Over 18 different antibody tests are available worldwide although they are not approved by any regulatory body. International experts have shown they can perform poorly and "often lead to misdiagnosis, mistreatment and potential harm to public health". WHO strongly recommends that antibody tests should not be used for the diagnosis of TB.