Serological IgG, IgM and IgA diagnosis and prognosis of mycobacterial diseases in routine practice

The routine diagnosis of tuberculosis and other mycobacterial diseases based on organism identification was completed during a period of one year in 730 patients, with serological IgG, IgM and IgA determination of antibodies against antigen 60 from M. bovis , strain BCG. The analysis was performed on 10 groups of patients consisting of 1) inflammatory diseases of the respiratory tract, 2) pericarditis, myocarditis, lymphadenitis and CNS diseases, 3) chronic non-inflammatory diseases of kidneys, liver and pancreas, 4) non-inflammatory diseases of the heart, sarcoidosis and pneumoconiosis, 5) tumor, 6) healthy people with TB contact, 7) inactive TB, 8) culture-positive pulmonary and extra-pulmonary TB, 9) culture-negative TB and extra-pulmonary TB, and 10) potentially pathogenic mycobacteria. The specificity of the test (100% negative cases in Group 6, composed of healthy people) is estimated at about 90%, in accordance with determinations made in other laboratories. In non-tuberculous patients, the specificity varied according to the analysed groups. Group 1 was largely unspecific for IgM (76% positives) but the specificity was acceptable for IgG (6.2% positives ) and IgA (7.4% positives). Group 2 was similar to Group 1. Group 3 was associated with positive IgA titers. Group 4 was only exceptiony seropositive and Group 5 was positive mainly for IgA (11. 4%) associated with lower respiratory tract ailments. This unspecific seropositivity was attributed to inapparent infections by PPM whose colonisation was favored by the particular disease of the patients. The sensitivity of serological measurements applied to the diagnosis of TB patients and PPM patients was similar, regardless if the disease was pulmonary or non-pulmonary, regardless if cultures were positive or not and, in our hands, was low (positivity for IgA about 30 %, for IgM about 10% and for IgG about 30%). This poor sensitivity observed with people presenting for treatment is attributed to an immune depression occuring mainly in elderly patients. The remarkable sensitivity of the serological instrument applied to culture-negative pulmonary and non-pulmonary TB cases as well as PPM cases makes the test a good adjuvant in cases of suspicion of TB. The assessment of the serological status of people under chemotherapy is worth the analysis, a high IgG level being associated with immunocompetence while the absence of IgG antibodies and/or the presence of IgA antibodies denotes an immunologically misdirected response potentially opening the way to chronic infections.