Evaluation of the diagnostic value of measuring IgG, IgM and IgA antibodies to the recombinant 16-kilodalton antigen of Mycobacterium tuberculosis inchildhood tuberculosis

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 cont act children and 149 children suffering from non-mycobacterial diseases wer e evaluated. Detection of anti 16-kDa antigen IgG, IgM and IgA was performe d by enzyme-immunoassay. RESULTS: An increased mean antibody response to re-Ag16 was observed in con tact 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 dise ase patients, respectively), indicating that anti-16-kDa antibodies could b e elevated in response to infections even without clinically apparent TB. S etting 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% positi vity in children with active TB. CONCLUSION: The detection of anti 16-kDa IgG and IgA may be useful as a com plementary technique for the diagnosis of childhood TB. Recognition of this antigen seems to be heterogeneous; combining responses against other antig ens may be a good strategy to improve the performance of this assay.