Diagnostic utility of estimation of mycobacterial antigen A60 specific immunoglobulins in serum and CSF in adult neurotuberculosis.

An ELISA assay based on mycobacterial antigen A60 (Anda, Biologicals France) was used to detect specific immunoglobulins (IgM, IgA and IgG) in 48 cases of adult neurotuberculosis (24 TBM; 24 Tuberculoma) and in 48 controls (24 diseased controls; 24 healthy controls). Serum was analysed in all the subjects whereas CSF was assayed only in TBM cases and diseased controls. The cut off values used for IgM, IgG and IgA in this study were 1.500 ODI (optical density index) at 1:100 dil, 250 units/ml and 150units/ml respectively in serum; and 1.500 ODI at 1:10 dil, 10 units/ml and 10 units/ml respectively in CSF. The mean titres of all three antibodies were found to be significantly higher in cases as compared to controls. In cases of TBM, in serum, the percentage positivity for IgM, IgG, IgA and combination of IgG or IgA were 41.67, 87.50 87.50 and 95.83 respectively. The corresponding figures in CSF were 62.50, 75.0, 66.67 and 79.16 for IgM, IgG, IgA and 'IgA or IgM' respectively. In tuberculoma cases, in serum, the figures were 37.50, 75.0, 75.0 and 83.33 respectively. Overall, a high sensitivity and specificity were obtained in cases of TBM (Serum: ST = 95.83%: SP = 87.50%; CSF ST = 79.16%. SP = 100%) and Tuberculoma cases (serum: ST = 83.33% SP = 87.50%) employing the combined antibody estimations.