Purified protein derivative test and its booster phenomenon in patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is a common disease in the community, with various complications. An appropriate solution is immunosuppressive drugs, which may lead to weakening of the cellular immune system and body unresponsiveness to tuberculosis (TB). As TB sensitivity is determined by the amount of induration created in the Purified Protein Derivative (PPD) test, this study aims to evaluate the immune response to the PPD test and its booster in RA patients.

This cross-sectional study was performed on rheumatoid arthritis patients referred to Alzahra Hospital, Isfahan, treated with ‹20 mg glucocorticoid daily or 7.5 mg Methotrexate (MTX) weekly. The sampling method was simple and accessible. The PPD test was performed in patients using the Mantoux method after 72 hours, and seven days later, the results were interpreted in 72 hours after the PPD booster injection. Induration ≥5 mm was considered to be positive. The data was analyzed using the SPSS software.

Nineteen patients had positive results in the initial and reminder tests and 81 patients had negative results in both tests. Six patients (6.9%) with negative results in the initial test changed to positive in the reminder test. There was no positive result in the initial test and negative result in the reminder one. The frequency distribution of the reminder test, based on the initial test was significant (P < 0.001). Also, the McNemar test showed that the changes in the reminder test based on the initial test had a significant difference (P = 0.031).

It seems that in the endemic and developing areas, the PPD booster is applicable for diagnosing latent tuberculosis in patients with rheumatoid arthritis.