Tuberculosis Assays Compared for Children at Risk

A blood test and a skin test have been compared for the diagnosis of tuberculosis in children who have different epidemiologic risk factors.

The performance of a commercial interferon-γ-release assay (IGR), and the tuberculin skin test (TST) was tested on a group of children who had been referred to tuberculosis clinics.

A prospective study of 210 children aged one month to 18 years, who were referred to three pediatric tuberculosis clinics from 2005 to 2006, was carried out at Baylor College of Medicine, (Houston, TX, USA). From the children examined, 27 were deemed low risk with no risk factors for tuberculosis; 78 children were deemed intermediate risk, with risk factors but no identifiable source; 74 children were deemed high risk that had contact with a known source case; and 31 children had active disease. All children were tested with both the TST (the Mantoux test) and the T-SPOT.TB IGR assay. Interferon-γ–release assays (IGRAs) detect interferon-γ generated by T cells in response to region of difference (RD1) antigens found in Mycobacterium tuberculosis.

The results of the study showed that 31 children (15%) were diagnosed with tuberculosis disease, 110 children (51%) had latent tuberculosis infection (LTBI) according to results of their TST, and 74 children (34%) were uninfected. For the 13 children with culture-confirmed tuberculosis disease, the sensitivity of the TST was 77%, and that of the T-SPOT.TB assay (Oxford Immunotec, Inc.; Marlborough, MA, USA), was 92%, while concordance was only 69%. In the high-risk children, concordance was 94% for children who had never been immunized and 88% for children immunized with the bacille Calmette-Guérin (BCG) vaccine. The investigators also report that, in multivariate analysis, contact with a source case was associated with a T-SPOT.TB result, but age and BCG immunization were not.

The authors concluded that the T-SPOT.TB assay was comparable to the TST for the identification of children with microbiologically confirmed tuberculosis disease and children at high risk with LTBI. T-SPOT.TB was more specific than the TST for children who were immunized with BCG and who were at intermediate risk for LTBI, a population for which optimizing specificity can decrease the need for unnecessary interventions. The study was published on line December 6, 2010 in Pediatrics.

Related Links:
Baylor College of Medicine
Oxford Immunotec