Tuberculin Skin Test, Interferon-gamma Assay, and T Cells Subpopulations in Hemodialysis Patients

Objective To examine and compare the responses of hemodialysis (HD) patients to Mycobacterium tuberculosis antigens by using the tuberculin skin test (TST) and an interferon γ assay (IFN-TB), and to investigate the relationship between T cells subpopulations and tests results. Observational, prospective, diagnostic study conducted in a HD center in a country with high prevalence of tuberculosis. Patients 195 patients on maintenance HD who consented to participate in this study; 187 (6 were excluded for refusing TST and 2 for indeterminate responses to IFN-TB) were HIV negative, vaccinated with the Bacille Calmette-Guerin vaccine, and without any signs of active tuberculosis, were selected. Methods Similar to the Mantoux method, 10 IU tuberculin was used for the TST. An IFN-γ assay specific for Mycobacterium tuberculosis antigens and phytohemagglutinin was carried out. Flow cytometry analysis of peripheral lymphocytes was also performed. Results TST and IFN-TB results were found to be positive (44% and 53%, respectively) or negative (32% and 47%, respectively) in similar proportions. Results were in agreement in 71% of positive and 58% of negative tests. IFN-γ levels were found to be higher in patients with a positive TST. All cell counts and CD4/CD8 were found to be higher in TST-positive patients, whereas only total lymphocytes count and CD4/CD8 were reported to be high in IFN-TB-positive patients. A model of multivariable linear regression including cell counts explained 16% of the mitogen-induced IFN-γ production ( F = 5,11; P = .0003). The majority of subjects with positive tests were younger, in most cases male, belonged to the Roma ethnic group, had a shorter HD vintage, and a better nutritional status. Conclusions TST and IFN-γ production stimulated by Mycobacterium tuberculosis antigens rely on patient's immune status, which could be influenced by either individual (age, gender), dialysis-related (HD vintage), or nutritional factors. In addition, the diagnostic utility for tuberculosis is similar and moderate in HD patients.