Background and aim: To study the pattern of tuberculin sensitivity and its interpretation to diagnose sarcoidosis in the presence of a high prevalence of Mantoux positivity in the general population in India.
Methods: Tuberculin sensitivity was examined in two groups of subjects: Group I included 50 newly diagnosed patients with pulmonary sarcoidosis and two control subjects with pulmonary ailments other than sarcoidosis or tuberculosis for each case; Group II included 62 new patients with sarcoidosis and 130 healthy volunteers as control subjects. Mantoux test was performed using 1 TU tuberculin. The test was repeated with 5 TU tuberculin for those cases and controls who were anergic to 1 TU among the group II subjects. Sensitivity and specificity for a "negative Mantoux test" in sarcoidosis were calculated at different cutoff points. The influence of prior BCG vaccination status on the performance of Mantoux test was also studied.
Measurements and results: Forty-six (92%) of the 50 patients with sarcoidosis in Group I and 55 of the 62 (88.7%) in Group II did not show any reaction to Mantoux test, compared to 32 (32%) and 21 (16.2%) controls, respectively in groups I and II (P < 0.001). Thirty-nine (70.9%) of the 55 patients and 6 (28.6%) of the 21 controls from the group II subjects who were tested again with 5 TU did not show any reaction. A negative Mantoux test had a high sensitivity value at all the cut off points for the diagnosis of sarcoidosis. BCG vaccination administered during childhood had no correlation with a negative Mantoux reaction.
Conclusions: Tuberculin anergy in sarcoidosis is not influenced by the rate of Mantoux positivity in the general population. A positive Mantoux test (irrespective of the size of reaction) in a suspected case of sarcoidosis should arouse strong suspicion of an alternate or an additional diagnosis of tuberculosis.