Evaluation of Serological Tests Using A60 Antigen for Diagnosis of Tuberculosis

Identification of acid-fast bacilli (AFB) in sputum or tissue samples is among definite diagnostic methods of tuberculosis. However, this method of diagnosis is restricted by certain limitations.  Serologic diagnosis of tuberculosis (TB) has been used for a long time. The aim of this study was to determine the sensitivity and, specificity of Antigen 60 (A60) IgG, IgA, IgM test results in TB diagnosis. Mycobacterial A60-based ELISA was used to measure specific IgA, IgM and IgG antibodies in the sera of 127 adult TB patients (consisted of 74 pulmonary and 53 extra-pulmonary cases), and 95 controls (46 healthy volunteers and 49 patients with various acute or chronic diseases other than tuberculosis). Data from A60 IgG-based ELISA, chest radiography, AFB culture and pathologic evaluation for AFB were obtained .The cutoff value of A60 IgG, IgA and IgM were chosen according to a receiver operating characteristic (ROC) analysis. The sensitivity, specificity and positive likelihood ratio were determined. The mean levels of IgG, IgA and IgM were significantly higher in patients with pulmonary tuberculosis when compared with control groups. Sensitivity of IgG test was 54.3 %, while the specificity was 84.2%. The IgA test showed a sensitivity of 70.1% with a specificity of 80 %. Combination of the IgG and IgA tests showed a total sensitivity of 45.7 % and a specificity of 94.7% and the positive likelihood ratio of 8.62.  Chosen cutoff values of IgG, IgA, and IgM sets were 285,265 and 0.9 ELISA units respectively. Our study results showed a good specificity (94.7%) and a reasonable positive likelihood ratio (8.62) of the test when combined IgA and IgG with new cutoff points were considered on diagnosis of tuberculosis in adult patients. Combined use of both IgG and IgA tests results allows an increased accuracy in diagnostic of tuberculosis