Evaluation of the diagnostic value of measuring IgG, IgM and IgA antibodies to the recombinant 16-kilodalton antigen of mycobacterium tuberculosis in childhood tuberculosis

Abstract

Objective: To evaluate the usefulness of the recombinant 16-kDa antigen (re-Ag16) of Mycobacterium tuberculosis in the serodiagnosis of tuberculosis (TB) in children.

Materials: Seventy-four children with active TB, 49 apparently healthy contact children and 149 children suffering from non-mycobacterial diseases were evaluated. Detection of anti 16-kDa antigen IgG, IgM and IgA was performed by enzyme-immunoassay.

Results: An increased mean antibody response to re-Ag16 was observed in contact children compared with non-mycobacterial disease patients (IgG assay: 89.1 enzymatic units [eu] vs. 40.8 eu; IgM assay: 64.7 eu vs. 38.1 eu; IgA assay: 138.2 eu vs. 78.2 eu for contact children and non-mycobacterial disease patients, respectively), indicating that anti-16-kDa antibodies could be elevated in response to infections even without clinically apparent TB. Setting the specificity as the 95th percentile of the contact group's ELISA units, the sensitivity of the IgG, IgA and IgM assays were 34%, 19% and 3% respectively; combining results of the IgG and IgA assays led to 43% positivity in children with active TB.

Conclusion: The detection of anti 16-kDa IgG and IgA may be useful as a complementary technique for the diagnosis of childhood TB. Recognition of this antigen seems to be heterogeneous; combining responses against other antigens may be a good strategy to improve the performance of this assay.