Interferon Gamma Release Assay and Tuberculin Skin Test in the Diagnosis of Latent Tuberculosis among Health Care Workers – A Comparative Study

Health Care Workers (HCWs) are vulnerable to tuberculosis exposure. Non availability of a reliable test has resulted in underestimation of latent tuberculosis infection (LTBI) among HCWs. The aim is to detect the rate of LTBI among nursing and medical students, Compare Interferon Gamma Release Assay (IGRA) and Tuberculin Skin Test (TST), Detect conversions and reversions. Total of 100 (83 nursing and 17 medical) students were included in the study. QuantiFERON®-TB Gold In-Tube test (QFT) and TST were carried out for the participants and results at various thresholds were noted. The prevalence of LTBI was found to be 16 - 26% among the students using TST and 7 – 8% using QFT. TST The conversion was 2.5% for TST and 2.5 % for QFT when thresholds were kept low. The conversion was 7.5% for TST and 2.5 % for QFT, with stringent threshold. With low thresholds, 25% students had reversions and with stringent threshold values 20% had reversion. No single test is reliable for detecting LTBI. Routine TST and IGRA of HCWs with patient contact should be part of the screening program with a major effort to institute treatment for LTBI.