Humoral immune response against 38-kDa and 16-kDa mycobacterial antigens in bone and joint tuberculosis

The diagnosis of bone and joint tuberculosis (BTB) is difficult, and diagnostic delays often occur. A reliable serological test detecting anti-mycobacterial antibodies would thus be of some use in this form of the disease.

To evaluate the diagnostic accuracy of an assay detecting IgG against 38-kDa and 16-kDa recombinant mycobacterial antigens in BTB.

In a prospective study, serum samples from 124 subjects were examined: 30 BTB cases, 40 non-specific bone and joint infection patients (NSBI), 30 lung cancer patients (LC), and 24 healthy volunteers (HC). An ELISA-based test (Pathozyme TB complex plus) was used.

The cut-off level was established at 150 U/ml according to receiver operating characteristic (ROC) curves. The quantified level of sensitivity of the test detecting BTB was 56%, at a specificity of 99%. The positive and negative predictive values were respectively 94% and 88%. Mean IgG level in the BTB group was 470 +/- 761 U/ml (mean +/- SD), and was significantly higher than the antibody level in the control groups (NSBI 58 +/- 42 U/ml, LC 43 +/- 38 U/ml, HC 40 +/- 29 U/ml).

The test presents an acceptable level of sensitivity and very good specificity in the diagnosis of BTB, and can be used in combination with other methods to increase diagnostic accuracy in this disease.