Use of the T-SPOT.TB Assay to Detect Latent Tuberculosis Infection Among Rheumatic Disease Patients on Immunosuppressive Therapy

Objective. We evaluated the T-SPOT. TB assay to identify latent tuberculosis infection (LTBI) in patients with rheumatic disease receiving immunosuppressive medication including tumor necrosis factor (TNF) antagonists. Methods. A total of 200 patients seen in the Arthritis Center at Brigham and Women’s Hospital were enrolled for study. Most patients were US-born women with rheumatoid arthritis. A medical history was obtained using a questionnaire, whole blood was drawn for the T-SPOT. TB assay, and tuberculin skin testing (TST) was performed. Results. Both tests were performed on 179 subjects, who had no history of a positive TST. All subjects had a strong response to the T-SPOT. TB test positive control, and there were no indeterminate results. Among these 179 subjects, 2 had a positive TST and 10 had a positive T-SPOT. TB test. No subject was positive for both tests. Patients with a positive T-SPOT. TB test did not have typical risk factors for LTBI based on clinical evaluation. Conclusion. The lack of concordance between the TST and the T-SPOT. TB assay may indicate that the immunoassay is more sensitive, particularly in a patient population taking immunosuppressive medications. It is equally likely that the low prevalence of LTBI in this low-risk population led to an increase in the false-positive rate despite the high sensitivity and specificity of the T-SPOT. TB assay. In the context of our patient population, the T-SPOT. TB assay is likely to be most useful in evaluation of patients with a positive TST, since these patients have a higher pretest probability of having LTBI.