Comparison of Interferon-Gamma Release and Tuberculin Skin Test for Detection of Latent Tuberculosis Infections in Iranian Elderly Patients

Tuberculin skin test is a common method for diagnosis of latent tuberculosis but it has a high rate of false positivity and false negativity. In Quantiferon test, the interferon gamma secreted by lymphocytes in response to Mycobacterium tuberculosis antigens is measured. This study aimed to determine the rate of agreement between quantiferon with skin tuberculin induration in the diagnosis of latent tuberculosis in elderly.
This study was carried out in 2015 on 10 elderly patients with confirmed active tuberculosis, 30 elderly patients with latent tuberculosis and 50 elderly individuals without any respiratory symptoms at Iran University of Medical Sciences, Tehran, Iran. The secretion of gamma interferon of specific T cells in peripheral blood was measured using Quantiferon test. In addition the tuberculin skin test was performed using standard methods and the skin induration was measured. By drawing the ROC curve, sensitivity, specificity, and under the curve area (AUC) was calculated interferon gamma release and tuberculin test. Results of patients and healthy people were compared with the Kruskal-Wallis test.
The sensitivity and specificity of gamma interferon release test for active tuberculosis in elderly patients was, 100% and 98% respectively (area under the curve 0.99) while the sensitivity and specificity of the tuberculin test was respectively 80% and 94% (area under the curve 0.89). Regarding to elderly patients with latent tuberculosis the sensitivity and specificity of interferon-gamma release test was 73% and 98%, respectively; and the sensitivity and specificity of tuberculin test in these patients was 36% and 94%, respectively.
Quantiferon is more sensitive and specific test for diagnosis of latent tuberculosis and application of this method is more reliable for diagnosis of latent tuberculosis infection in the elderly.