Reproducibility of interferon gamma (IFN-γ) release assays a systematic review

Saloua Tagmouti, Madeline Slater, Andrea Benedetti, Sra V. Kik, Niaz Banaei, Adithya Cattamanchi, John Metcalfe, David Dowdy, Richard Zyl Van Smit, Nini Dendukuri, Madhukar Pai, Claudia Denkinger

Research output: Contribution to journalArticlepeer-review

64 Scopus citations


Rationale: Interferon gamma (IFN-γ) release assays for latent tuberculosis infection result in a larger-than-expected number of conversions and reversions in occupational screening programs, and reproducibility of test results is a concern. Objectives: Knowledge of the relative contribution and extent of the individual sources of variability (immunological, preanalytical, or analytical) could help optimize testing protocols. Methods: We performed a systematic review of studies published by October 2013 on all potential sources of variability of commercial IFN-γ release assays (QuantiFERON-TB Gold In-Tube and T-SPOT.TB). The included studies assessed test variability under identical conditions and under different conditions (the latter both overall and stratified by individual sources of variability). Linear mixed effects models were used to estimate within-subject SD. Measurements and Main Results: We identified a total of 26 articles, including 7 studies analyzing variability under the same conditions, 10 studies analyzing variability with repeat testing over time under different conditions, and 19 studies reporting individual sources of variability. Most data were on QuantiFERON (only three studies on T-SPOT.TB). A considerable number of conversions and reversions were seen around the manufacturer-recommended cut-point. The estimated range of variability of IFN-γ response in QuantiFERON under identical conditions was ±0.47 IU/ml (coefficient of variation, 13%) and ±0.26 IU/ml (30%) for individuals with an initial IFN-γ response in the borderline range (0.25-0.80 IU/ml). The estimated range of variability in noncontrolled settings was substantially larger (±1.4 IU/ml; 60%). Blood volume inoculated into QuantiFERON tubes and preanalytic delay were identified as key sources of variability. Conclusions: This systematic review shows substantial variability with repeat IFN-γ release assays testing even under identical conditions, suggesting that reversions and conversions around the existing cut-point should be interpreted with caution.

Original languageEnglish (US)
Pages (from-to)1267-1276
Number of pages10
JournalAnnals of the American Thoracic Society
Issue number8
StatePublished - Oct 1 2014


  • Diagnostics
  • IFN-γ release assays
  • Reproducibility
  • Tuberculosis

ASJC Scopus subject areas

  • Pulmonary and Respiratory Medicine


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