To identify tuberculosis infection in rheumatic patients on infliximab by use of PPD testing prior to immunobiologic therapy.
This study comprised 157 patients undergoing infliximab treatment and 734 other patients undergoing laboratory screening for tuberculosis infection originating from several services. The Mantoux technique was used for PPD testing, and an induration of at least 5 mm was considered reactive status.
In the infliximab group, 13% of the patients reacted to PPD, while, in the other group, 27% of the patients reacted to PPD (χ² = 13; P = 0.0003). These patients were divided into categories: adults with chronic diseases, PPD reactivity of 22%; and other controls, PPD reactivity of 31%. This shows the heterogeneous response of that population (χ² = 7; P < 0.009). In the infliximab group, subdivided according to pathologies [rheumatoid arthritis (RA), ankylosing spondylitis (AS), and psoriatic arthritis (PA)], different reactivity rates were observed, the lowest value occurring among RA patients: (RA x AS: OR = 0.13; CI: 0.03-0.47; χ ² = 12; P = 0.0004) and (RA x PA: OR = 0.16; CI: 0.02-1.04; χ² Yates corrected = 3.6; P = 0.05). The PPD reactivity in the RA subgroup (4%) was also lower as compared with that of the chronic patients group (22%) (OR = 0.16; CI: 0.05-0.49; χ² = 14; P = 0.0002), even when reclassified into four subgroups: rheumatology (OR = 0.19; CI: 0.04-0.72), kidney transplantation (OR = 0.16; CI: 0.05-0.51), infectology (OR = 0.21; CI: 0.05-0.75), and other conditions (OR = 0.13; CI: 0.04-0.44).
The low prevalence of PPD reaction in this Brazilian population, mainly in chronic patients, with the worst performance among RA patients, showed that the test has limited value for diagnosis of tuberculosis infection in candidates to infliximab therapy.