Is interferon-gamma TB-testing in accordance with guidelines

Abstract number: P1947

Meyer C.N., Browatzki A.

Objectives: The purpose of this study was to outline the practical use and clinical value of Quantiferon-TB-Gold (QFT-G) testing in the immuno-diagnosis of M. tuberculosis infection. The main indication for the test is diagnosing latent M. tuberculosis infection.

Methods: A retrospective study of all patients tested for M. tuberculosis infection by the QFT-G test (Celletis International, Australia) from the 1st of January 2005 to the 31st of December 2006 in a Danish regional hospital.

Results: The QFT-G test was performed in 91 patients. With the intention of diagnosing active TB (n = 69), the sensitivity was 80% (8/10, CI=0.55–1.00), specificity was 85% (50/59), PPV was 47% (8/17), and NPV was 96% (50/52). Thus, the positive likelihood ratio (LR) was 5.3 (95% CI 2.7–10.4), and the negative LR was 0.24 (95% CI 0.07–0.8).

The doctors prescribing the QFT-G test were specialists of internal or respiratory medicine (58%, 43/74), infectious diseases (11%, 8/74), haematology (1%, 1/74), dermatology (3%, 2/74), or were junior doctors (13%, 10/74). In 13% (10/74), the prescribing doctor could not be identified.

With a suboptimal diagnostic setup, the diagnosis of lung cancer was delayed three months in one patient with a positive QFT-G. For LTBI, the QFT-G test's approximated sensitivity was 33% (1/3), specificity was 93% (13/14), PPV was 50% (1/2), and the NPV was 87% (13/15), when QFT-G test and Tuberculin Skin Tests were used with the intention of diagnosing LTBI (n = 17) where no gold-standard exists.

Conclusion: The QFT-G test had a relatively low sensitivity and a low accuracy in diagnosing active TB, but it was widely used for that purpose. This was contrasting most international guidelines. As most of the prescribing doctors were specialists, it can be assumed that a great deal of uncertainty surrounds the indications for using this relatively new test.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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