A borderline range for Quantiferon Gold In-Tube results

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Objective: Interferon gamma release assays like Quantiferon Gold In-Tube (QFT) are used to identify individuals infected with Mycobacterium tuberculosis. A dichotomous cut-off (0.35 IU/ml) defines a positive QFT without considering test variability. Our objective was to evaluate the introduction of a borderline range under routine conditions. Methods: Results of routine QFT samples from Sweden (2009–2014) were collected. A borderline range (0.20–0.99 IU/ml) was introduced in 2010 recommending a follow-up sample. The association between borderline results and incident active TB within 3 to 24 months was investigated through linkage with the national TB-register. Results: Using the recommended QFT cut-off, 75.1% tests were negative, 21.4% positive and 3.5% indeterminate. In total, 9% (3656/40773) were within the borderline range. In follow-up samples, individuals with initial results between 0.20–0.34 IU/ml and 0.35–0.99 IU/ml displayed negative results below the borderline range (<0.20 IU/ml) in 66.1% (230/348) and 42.5% (285/671) respectively, and none developed incident TB. Among 6712 individuals with a positive initial test >0.99 IU/ml, 65 (0.97%) developed incident TB within 3–24 months. Conclusions: We recommend retesting of subjects with QFT results in the range 0.20–0.99 IU/ml to enhance reliability and validity of the test. Half of the subjects in the borderline range will be negative at a level <0.20 IU/ml when retested and have a very low risk of developing incident active TB.


  • Jerker Jonsson
  • Anna Westman
  • Judith Bruchfeld
  • Erik Sturegård
  • Hans Gaines
  • Thomas Schön
Enheter & grupper
Externa organisationer
  • Public Health Agency of Sweden
  • Karolinska Institute
  • Danderyd Hospital
  • Karolinska University Hospital
  • Kalmar County Hospital
  • Linköping University

Ämnesklassifikation (UKÄ) – OBLIGATORISK

  • Infektionsmedicin
TidskriftPLoS ONE
Utgåva nummer11
StatusPublished - 2017 nov 1
Peer review utfördJa