To test the validity of an augmented tuberculosis skin test (a-TST) combined with Quantiferon TB-gold
Standard TST using 1 tuberculin unit (TU) of purified protein derivative (PPD, RT23 strain) was carried out. If the positivity was less as compared to the general population, then a-TST using 10 TU PPD was employed. Simultaneously, QFTG test was also performed.
Using standard TST, 6/44 (13.6%), patients were positive compared to the reported figures of ~ 40% of the general population; 38 of the remaining TST-negative patients were then given an a-TST with 10 TU PPD; eight of them dropped out. Of the remaining 30 patients, eight (26.6%) were positive. Another 70 patients tested directly with a-TST; 22 (31.4%) were found positive. Thus, of a total of 100 patients tested with a-TST, 30 (30%) were positive. In 54 a-TST negative patients, QFTG was done; seven (13%) were positive. Thus, in combined a-TST with QFTG, 43% of the RA patients were found positive, suggestive of the presence of LTBI.
Combined a-TST with QFTG testing gave 43% positivity among RA patients, which is close to the reported ~ 40% Mantoux positivity in the general population. Therefore, this method for the screening of LTBI in Indian patients with RA being considered for tumor necrosis factor alpha treatment could be satisfactory for offsetting TB flare. It may apply to other high-burden TB countries around the world.