Diagnostic Value of Serological Tests (IgA, IgG, IgM) Against A-60 Antigen in Tuberculosis

Background: Tuberculosis (TB) is a common infectious disease worldwide especially in developing countries. Diagnosis of TB is difficult and often needs paraclinical studies. Measuring immunoglobulin's against A-60 antigen of TB microorganism has been reported as a useful technique. The aim of the present study was to evaluate the diagnostic value of serologic test (IgA, IgM, IgG) against A-60 antigen in tuberculosis.

Patients and methods: For this case-control study, 176 TB patients (124 patients with smear-positive pulmonary TB and 52 patients with extra pulmonary TB) and 283 healthy controls were enrolled. Then, all subjects were tested for IgM, IgA and IgG against A-60 antigen using ELISA technique.

Results: Sensitivities of IgM, IgG and IgA test were 15%, 25% and 40%, respectively while the following specificities were also reported 100%, 75% and 90%, respectively. Positive predictive values (PPV) were 100%, 57% and 72%, however, negative predictive values (NPV) were 65%, 72% and 70%, respectively. Combination of immunoglobulins' results increased sensitivity, for which the most sensitivity was observed in combination of IgG and IgA results.

Conclusion: Our results revealed the usefulness of serologic testing in TB diagnosis. Although its sensitivity is not high enough, combination of immunoglobulin results may improve the sensitivity.