INTERFERON GAMMA RELEASE ASSAY AMONG TUBERCULOSIS CULTURE POSITIVE AND NEGATIVE CASES TO DETERMINE CUT OFF VALUE

Abstract

Objective: To determine cut off value of Interferon Gamma Release Assay (IGRA) among Tuberculosis (TB) suspected patients and to compare median Interferon Gamma Release Assay value for Tuberculosis culture positive and culture negative patients.

Study Design: Cross sectional study.

Place and Duration of Study: Department of Microbiology, Armed Forces Institute of Pathology, National University of Medical Sciences, from Oct 2015 to Apr 2016.

Methodology: The study was conducted on patients with suspected tuberculosis. Quantiferon Tuberculosis Gold that has an important role in the immune response to Tuberculosis was performed by Enzyme Linked Immunosorbent Assay method and specimens were cultured on Mycobacterium Growth Indicator Tube 960 System (MGIT 960 system). Quantiferon Tuberculosis Gold values obtained by Enzyme Linked Immunosorbent Assay method were used to determine the sensitivity and specificity of this test.

Results: A total of 240 suspected isolates of tuberculosis during the study period were subjected to culture using MGIT 960 system, as per recommended protocol for the method. These samples were also subjected to Quantiferon TB Gold (QTBG) to measure Interferon Gamma Release Assay release. Sensitivity and specificity of IGRA was determined keeping tuberculosis culture as gold standard for this study.

Conclusion: Sensitivity and specificity values showed a significant p-value <0.001 with active tuberculosis. In TB endemic areas like Pakistan, new cutoff value must be kept in mind while interpreting results of IGRA.