Summary

Background:

Determining the accuracy of interferon gamma-releasing assays (IGRAs) is difficult due to the lack of a gold standard test for diagnosing latent tuberculosis (LTB). 

Objectives:

To analyze the guidelines used for interpreting IGRAs in determining prophylactic treatment management for latent tuberculosis (LTB) in Israel.

Methods:

We analyzed the retrospective data of 367 subjects who were referred to our laboratory during the period 2007–2011 for QuantiFERON Test-Gold In Tube (QFT-GIT) tests because of suspected LTB. Demographics and clinical data were retrieved from a questionnaire at enrollment, and 166/367 (45%) were further interviewed by phone in order to complete follow-up information on prophylactic TB treatment. 

Results:

The majority of subjects (116/166, 69.9%, P < 0.0001) were spared prophylactic treatment subsequent to QFT-GIT testing. Subjects with negative QFT-GIT and positive tuberculin skin test (TST) results who were BCG-vaccinated had the lowest treatment rates (6/68, 8.8%, P < 0.0001). Most BCG-vaccinated subjects with positive TST and negative QFT-GIT test results received treatment with anti-tumor necrosis factor-alpha (TNFα) (17/19, 89.5%, P = 0.004). We found more negative QFT-GIT test results in subjects who were receiving anti-TNFα or steroid and other immunosuppressive treatment prior to testing (11/11, 100%, P = 0.029; 22/26, 84.6%, P = 0.06; 15/17, 88%, P = 0.06, respectively). 

Conclusions:

Deciding on LTB prophylactic treatment in Israel is highly influenced by QFT-GIT test results. QFT-GIT findings contribute to clinical decisions, but their interpretation must also consider the patient’s medical history and clinical characteristics.