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A borderline range for Quantiferon Gold In-Tube results
Jerker Jonsson1,2, Anna Westman3,4, Judith Bruchfeld2,5
1The Public Health Agency of Sweden, Solna, Sweden.
Plos One
|November 3, 2017
Summary
Retesting individuals with borderline Interferon gamma release assay (Quantiferon Gold In-Tube or QFT) results improves test accuracy. A significant portion of borderline results become negative upon retesting, indicating a low risk of active tuberculosis.
Area of Science:
- Infectious Diseases
- Immunology
- Clinical Diagnostics
Background:
- Interferon gamma release assays (IGRAs) like Quantiferon Gold In-Tube (QFT) are crucial for diagnosing Mycobacterium tuberculosis infection.
- Current QFT interpretation uses a dichotomous cut-off (0.35 IU/ml), potentially overlooking test variability.
Purpose of the Study:
- To evaluate the effectiveness of introducing a borderline range for QFT testing under routine clinical conditions.
- To assess the association between borderline QFT results and the incidence of active tuberculosis.
Main Methods:
- Analysis of routine QFT results from Sweden (2009-2014).
- Implementation of a borderline range (0.20-0.99 IU/ml) with recommended follow-up testing.
- Linkage with the national TB register to track incident active TB cases.
Main Results:
- A total of 9% of QFT tests fell within the borderline range (0.20-0.99 IU/ml).
- Retesting showed that 66.1% and 42.5% of individuals with initial borderline results (0.20-0.34 and 0.35-0.99 IU/ml, respectively) became negative (<0.20 IU/ml).
- No incident active TB cases were observed in individuals with initial borderline results.
Conclusions:
- Retesting individuals with QFT results in the 0.20-0.99 IU/ml range enhances test reliability and validity.
- Approximately half of subjects with borderline QFT results retest negative (<0.20 IU/ml) and exhibit a very low risk of developing active tuberculosis.
