Tuberculin skin test is not informative in patients with rheumatoid arthritis

A tuberculin skin test (derived from purified protein) is the only widely used diagnostic method for latent tuberculosis worldwide. A positive test result is due to the occurrence of an immune response by T lymphocytes in infected individuals. Immune system dysfunction, especially in patients with rheumatoid arthritis, can lead to an inadequate response to the administration of tuberculin.

The aim of the comparative study by D. Ponce de Leon et al. (Peru), was an evaluation of the efficacy of a tuberculin skin test in the diagnosis of latent tuberculosis infection in patients with rheumatoid arthritis. The study was carried out in an endemic region of tuberculosis, the incidence of latent forms of tuberculosis in which reached 68% among the population over 25 years. 112 rheumatoid arthritis patients and 96 relatively healthy immunocompetent volunteers underwent a tuberculin skin test (Mantoux test) with an evaluation of the results after 72 hours. The reaction was considered negative with papule sizes less than 5 mm. The patients in the two groups did not differ significantly by age, sex, history of BCG vaccination, or indications of contact with tuberculosis patients.

According to the results, the average size of the papules in patients with rheumatoid arthritis was significantly lower than that of the control group (4.5 mm vs 11.5 mm, p less than 0.01). In 79 patients with rheumatoid arthritis (70.6%) compared to 25 (26%) in the control group, a negative reaction to the sample was observed (p less than 0.01). No effect of the duration and / or activity of the course of rheumatoid arthritis on the results was revealed.

As the researchers conclude, a tuberculin skin test cannot be considered an adequate method for the diagnosis of latent tuberculosis in patients with rheumatoid arthritis.