From the Guidelines
The false positive rate for a QuantiFERON-TB Gold test is generally low, approximately 2-3%, as indicated by the most recent and highest quality study 1. This means that about 2-3% of people without TB infection may receive a positive test result. False positives can occur due to several factors including:
- Laboratory error
- Cross-reactivity with non-tuberculous mycobacteria
- Recent vaccination with live vaccines
- Immune system activation from other conditions Healthcare providers should interpret positive results in the context of the patient's TB risk factors, clinical symptoms, and other diagnostic tests. For patients with low TB risk factors who test positive, repeating the test or performing an alternative test like the tuberculin skin test may be warranted to confirm the result. Understanding this false positive rate is important when using QuantiFERON testing for TB screening, especially in low-prevalence populations where positive predictive value decreases, as noted in the guidelines for using interferon gamma release assays to detect Mycobacterium tuberculosis infection 1. It is essential to consider the patient's overall clinical picture and risk factors when interpreting QuantiFERON test results to minimize the impact of false positives on morbidity, mortality, and quality of life.
From the Research
False Positive Rate for QuantiFERON-TB Gold Test
- The false positive rate for the QuantiFERON-TB Gold test is not explicitly stated in the provided studies.
- However, study 2 mentions that the test allows to eliminate the false positive of the skin test, with a rate of 1.6.
- Study 3 reports a specificity of 85.7% for the QuantiFERON-TB Gold test, which implies a false positive rate of 14.3%.
- Study 4 found that the frequency of positive results tended to be higher in MTB(-) sarcoidosis patients (24.3% vs. 13.5% for the control group), but this difference was not statistically significant.
Factors Influencing False Positive Results
- Study 5 investigated factors that influence false-negative results of the QFT-GIT test, but did not specifically address false positive results.
- Study 4 found that sarcoidosis activity does not negatively influence the result of the QFT-GIT test.
- Study 3 found that the specificity of the QuantiFERON-TB Gold test was not affected by prior BCG vaccination or corticosteroid therapy.
Clinical Implications
- Study 2 suggests that the QuantiFERON-TB Gold test can help avoid unnecessary treatments and unwanted effects of antituberculosis medicines by eliminating false positive results.
- Study 3 recommends the use of IGRA tests, including the QuantiFERON-TB Gold test, as an alternative to the TST for detecting latent tuberculosis infection in patients with rheumatic disease prior to anti-TNF therapy.