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Canadian Journal of Infectious Diseases and Medical Microbiology
Volume 23, Issue 4, Pages 183-186
http://dx.doi.org/10.1155/2012/838465
Original Article

Application and Interpretation of an Interferon-Gamma Release Assay: Results of an Audit in a Canadian Centre

Sopharat Vat,1 Marc Ghannoum,2 Pierre Laflamme,3 Mario Dugas,4 Manon Labrecque,4 and Valéry Lavergne3

1Université de Montréal, Hôpital de Verdun, Canada
2Département de médecine interne, Hôpital de Verdun, Canada
3Département de microbiologie médicale et infectiologie, Hôpital du Sacré-Coeur de Montréal, Montréal, Québec, Canada
4Département de pneumologie, Hôpital du Sacré-Coeur de Montréal, Montréal, Québec, Canada

Copyright © 2012 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

BACKGROUND: Interferon-gamma release assays (IGRAs) are newly approved for diagnosing latent tuberculosis infection (LTBI). An internal audit was conducted to review the use of a newly implemented IGRA at the Hôpital du Sacré-Coeur de Montréal (Montréal, Québec) to evaluate its concordance with Canadian recommendations and its implication on diagnosis.

METHODS: From April 2007 to January 2009, all Quantiferon TB Gold In-Tube (QFT, Cellestis inc, USA) tests performed in at the Hôpital du Sacré-Coeur de Montréal were retrieved. Strategies used to investigate LTBI and clinical interpretation of test results were compared with the local algorithm, which is derived from the current national guidelines.

RESULTS: A total of 200 patients tested with QFT were included in the analysis. LTBI investigation and QFT testing were considered to be appropriate in 87.5% and 66.5% of patients, respectively. Overall, 67 QFT tests were performed inappropriately; 25 were performed when a LTBI investigation was not indicated and 42 were performed whe LTBI interpretation was possible with the result of the tuberculin skin test alone. Among the 175 patients investigated appropriately for LTBI, 49 QFT tests (28%) were interpreted incorrectly; 32 patients (at high risk of developing active tuberculosis) had a positive tuberculin skin test and a negative QFT result wrongly interpreted as being negative for LTBI and 13 patients should have undergone further LTBI investigations.

CONCLUSION: Globally, the present study revealed that there are discrepancies on how the IGRA was employed and interpreted in a Montreal hospital and that strict compliance to the guidelines could significantly reduce errors in interpretation.