Detection of IgG and IgA against the mycobacterial antigen A60 in patients with extrapulmonary tuberculosis
- Marco Alifanoa,
- Roberto De Pascalisb,
- Matteo Sofiaa,
- Stanislao Faraonea,
- Mariassunta Del Pezzob,
- Italo Covellib
- aInstitute of Respiratory Disease, bInstitute of Clinical Microbiology, Department of Cellular and Molecular Biology and Pathology, cUniversity of Naples “Federico II”, Naples, Italy
- Dr M Alifano, Via Roma 60, I-81024 Maddaloni, Italy.
- Received 23 July 1997
- Revision requested 5 September 1997
- Revised 4 December 1997
- Accepted 21 January 1998
BACKGROUND Diagnosis of extrapulmonary tuberculosis is often difficult to establish using standard methods. Serological techniques based on detection of antibodies against mycobacterial antigen A60 have shown good sensitivity and specificity in pulmonary tuberculosis. The present study was undertaken to define the diagnostic accuracy of testing for IgG and IgA against A60 in extrapulmonary tuberculosis.
METHODS One hundred and ninety eight subjects were studied: 42 patients with extrapulmonary tuberculosis confirmed by microbiology and/or histology, 24 subjects with healed pulmonary or extrapulmonary tuberculosis, 44 patients with a defined non-tuberculous disease, and 88 healthy volunteers (44 PPD negative and 44 PPD positive). Detection of IgG and IgA against A60 antigen was carried out by enzyme-linked immunosorbent assay. Cut off values were determined by receiver operating characteristic curves.
RESULTS Sensitivity of the IgG test was 73.8% in extrapulmonary tuberculosis, while the specificity was 96.1%. The IgA test showed a sensitivity of 69.0% with a specificity of 93.6%. Combination of the IgG and IgA tests showed a sensitivity of 80.9% and a specificity of 92.3%. Patients with extrapulmonary tuberculosis showed significantly higher titres of both IgG and IgA against A60 than other groups.
CONCLUSIONS Anti-A60 IgG or IgA tests are characterised by good sensitivity and specificity. The combined use of both tests allows an increase in diagnostic accuracy of extrapulmonary tuberculosis.