Background: The diagnosis of extra-pulmonary tuberculosis (EPTB) by conventional methods such as culture and microscopy has low sensitivity and requires an invasive procedure. A simple rapid serological test would be of great value.
Methods: Six antigens (ESAT-6, Ag85A, TB10.4, Rv3881c, lipoarabinomannan (LAM) and Ara6-BSA) were tested in an ELISA to detect antigen specific IgG and IgM antibodies in sera from 54 culture and histology-confirmed tuberculous lymphadenitis (TBLN) patients, among whom four were HIV seropositive, sera from 25 smear positive pulmonary tuberculosis (PTB) patients, 15 culture and histology-negative lymphadenitis (non-TBLN) patients (n=15) and 22 healthy controls (HCs).
Results: The sensitivities of the antigens for the detection of IgG in sera of TBLN patients ranged from 4 to 30 %. Specificities ranged from 91 to 100 % with sera from HCs. Sensitivities of the antigens for detection of IgM ranged from 0 to 15 % and specificities ranged from 91 to 100 %. LAM was the most potent antigen followed by ESAT-6 and Rv3881c for detection of IgG. However, the sensitivity for antigen specific IgG antibody detection was improved when LAM was combined with ESAT-6 and Rv3881c.The sensitivity was 54 % and the specificity 91 %.
Conclusions: The study suggests that the combined use of LAM, ESAT-6 and Rv3881c for the detection of IgG in sera of TBLN patients could be a supplement to microscopy of fine- needle aspirate (FNA) to diagnose EPTB.