Tuberculin skin testing with purified protein derivative (PPD) is part of tuberculosis (TB) screening in patients receiving infliximab. We assessed whether infliximab, a strong inhibitor of inflammation, suppressed dermal induration, the outcome of this test. We also reassessed the booster phenomenon and the interobserver variability in tuberculin testing.
Forty-seven patients with various diagnoses, who had had a PPD test before infliximab use, were retested after infliximab treatment. The test was also assessed cross-sectionally among 31 patients with rheumatoid arthritis (RA) after 8.6 [+/- 4.1 standard deviation (SD)] months of infliximab use and in 82 patients with RA who had never used this agent. Booster phenomenon and the interobserver variability of reading the test were reassessed among 163 infliximab-naive patients with RA and Behcet's disease (BD) and 47 healthy controls.
Among the 47 patients who received infliximab, and for whom sequential data were available, the mean skin induration was 5.9 +/- 8.0 SD mm before and 6.1 +/- 7.5 mm after 4.8 +/- 3.7 months of treatment (p = 0.890). In the cross-sectional study the mean PPD induration was 7.8 +/- 8.4 mm among infliximab-naive patients with RA, while it was 6.6 +/- 2.1 mm in those receiving infliximab (p = 0.271). Booster phenomenon was observed in 14/49 (29%) of patients with RA, 7/31 (23%) of those with BD, and 1/10 of healthy controls. Interobserver variability of PPD reading was good (kappa = 0.92).
Infliximab use does not suppress the skin reaction to tuberculin. We confirm the booster phenomenon and that the PPD skin test has an acceptable interobserver reliability for an in vivo test.