Assessment of PPD Conversion Rate in Patients Receiving Tumor Necrosis Factor-alpha Inhibitor Drugs

Tumor necrosis factor-alpha (TNF-α) inhibitors are widely used in rheumatologic diseases but may increase the risk of primary tuberculosis (TB) infection or reactivation. Purified protein derivative (PPD) conversion is an important indicator of latent TB in immunosuppressed patients. This study aimed to determine the rate of PPD conversion and associated factors in patients receiving anti-TNF therapy.

This prospective study included adults with rheumatologic diseases who initiated anti-TNF therapy between March 2021 and September 2023. Patients with prior TB, previous anti-TNF exposure, or a positive baseline PPD were excluded. A PPD test was performed before treatment and repeated one year later. An induration ≥5 mm at follow-up was considered conversion.

Sixty patients completed the study (mean age 44.29 ± 14.70 years; 56.7% male). Six patients (10.0%) demonstrated PPD conversion after one year of anti-TNF therapy. Most conversions occurred in individuals with psoriatic arthritis (66.6%). No cases of active TB were detected clinically or radiologically. Statistical analysis showed no significant association between PPD conversion and age, sex, disease duration, anti-TNF type, methotrexate or corticosteroid use, diabetes mellitus, or hypertension. Psoriatic arthritis was the only factor significantly associated with conversion (P = 0.03).

Ten percent of patients receiving anti-TNF therapy developed PPD conversion, indicating new latent TB infection. Psoriatic arthritis was significantly associated with conversion, while medication type and other clinical factors were not. These findings support routine annual TB screening in anti-TNF recipients, particularly in regions with moderate or high TB prevalence.