Performance of QuantiFERON-TB-Gold in Tube Assay (QFG-IT) Versus Tuberculin Skin Test (TST) in Diagnosing Active and Latent TB Infection in a Low-Middle Income Country (LMIC)

Abstract

PURPOSE: To compare the performance of QFG-IT and TST tests in identifying active tuberculosis (TB) and latent tuberculosis infection (LTBI) in high TB burden settings in a LMIC. METHODS: We compared the 2 tests in a cohort of 210 participants classified into three groups; Group I investigated for LTBI and included 74 health care workers (HCWs), Group II; 83 patients investigated for active TB disease, Group III; 53 healthy control subjects. RESULTS: QFG-IT was positive in 31.1%, 48.2% 11.3% of the three groups, respectively. 10.0% from the enrolled cohort had indeterminate QFG-IT results. In patients investigated for active TB, QFG-IT was positive in 84.2% of pulmonary, and in 56.4% of extra-pulmonary TB proved cases. Sensitivity, specificity, positive and negative predictive values of QFG-IT were 65.62%, 80%, 95%, and 28.6%, meanwhile they were 90.57%, 50%, 90.57% and 33.33% for TST, respectively. Positive QFG-IT tests were associated with older age, female gender, BCG vaccination and longer duration of work in health care setting. Overall agreement between the 2 tests was moderate (75.66%, 0.526). CONCLUSIONS: We showed moderate agreement between TST and QFG-IT test in diagnosing LTBI and active TB infection in high burden setting. Despite higher specificity of QFG-IT test, TST remains a cost effective test in LMICs with limited budget for use of IGRA tests in national control programs. CLINICAL IMPLICATIONS: QFG-IT in conjunction with TST improves the diagnostic yield, justifying its use in difficult to diagnose situations in active TB. Also, it can help identifying at-risk groups and reduce the indication of preventive chemotherapy in high burden settings.