Ligia Petrescu

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 gamma 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-gamma 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-gamma 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-gamma 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-gamma production stimulated by Mycobacterium tuberculosis antigens rely on patients 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.