Comparison of plasma interferon-gamma and antigen 60 immunoglobulin G in diagnosing pulmonary Mycobacterium tuberculosis infection.

BACKGROUND An elevated interferon-gamma (IFN-gamma) level has been reported in the plasma of patients with pulmonary tuberculosis. Serologic diagnosis of tuberculosis using Antigen 60 immunoglobulin G (A60 IgG) is a well-known diagnostic approach. This study evaluated plasma IFN-y compared to A60 IgG in diagnosing Mycobacterium tuberculosis. METHODS This study recruited 65 patients with tuberculosis and 59 controls. The plasma levels of A60 IgG and IFN-gamma were measured using enzyme-linked immunosorbent assay kits. RESULTS The cutoff values of IFN-gamma and A60 IgG tests were set at 0.137 pg/ml and 261.2 units. The sensitivity and specificity of the IFN-gamma test were 27.7% and 91.5%. The positive and negative predictive values of the IFN-gamma test were 53.4% and 78.3%. Moreover, the sensitivity and specificity of the A60 IgG test were 53.8% and 67.8%. The positive and negative predictive values of the A60 IgG test were 37.0% and 80.7%. Finally, the sensitivity and specificity of the combined A60 IgG and IFN-gamma tests were 64.6% and 62.7%. The positive and negative predictive values of the combined A60 IgG and IFN-gamma tests were 37.8% and 83.4%. CONCLUSIONS The combined tests did not achieve significant improvement in disease prediction. The A60 IgG test and IFN-gamma test had similar diagnostic value in pulmonary Mycobacterium tuberculosis infection.