Short-Term Reproducibility of a Commercial Interferon Gamma Release Assay

Abstract

Interferon gamma release assays (IGRAs) have been shown to be sensitive and highly specific for the detection of immune memory against Mycobacterium tuberculosis. Little is known about the reproducibility and within-person variability of these assays. Various aspects of short-term reproducibility of a commercial IGRA, the QuantiFERON-TB Gold In-Tube (QFT-IT) assay, were assessed. The QFT-IT assay was performed twice within 3 days in 27 health care workers in Cape Town, South Africa. Two sets of tests were performed by different operators on day 1, and one set was performed on day 3. Aspects such as interoperator, intraoperator, day-to-day variability, and test-retest variability as well as different the storage methods of plasma were investigated. Seventeen of 27 (63%)

Within-Subject Variability of Mycobacterium tuberculosis-Specific Gamma Interferon Responses in German Health Care Workers

“…Data on the reproducibility and within-subject variability of IFN-␥ responses from well-designed studies is rare. Notably, most of the available data relates to high-incidence countries (6,32,34), and so far only a few preliminary results on IGRA repeatability and reproducibility among HCWs in the United States have been published (2). In line with results from previous studies, we found changes of Ϯ60 to 70% from the mean IFN-␥ responses for both IGRAs to be responsible for 95% of the within-subject variability.…”

“…Thus, it is not surprising that consensus on the definition and prognosis of IGRA conversions, reversions, and borderline zones still is lacking (22). To date, only a few studies systematically determined different components of technical and biological IGRA variability (6,34). A single study assessed within-subject variability in a head-tohead comparison between both commercial IGRAs (32), but no peer-reviewed study reporting data on the within-subject variability of IFN-␥ responses from a low-incidence setting has been published yet.…”

“…Two recently published systematic reviews on the within-subject variability and performance in the serial testing of HCWs identified only 4 and 10 studies, respectively, which met the predefined eligibility criteria (33,37). Studies on reproducibility and within-subject variability were predominantly from high-incidence settings (India and South Africa) and included only small numbers of subjects (67 in total) (6,32,34). In contrast, serial testing studies were mostly from countries with a low to intermediate TB incidence (5,13,20,(24)(25)(26)36).…”

Reproducibility of Interferon Gamma (IFN-γ) Release Assays. A Systematic Review

“…The overall quality of the selected studies as assessed by the modified quality appraisal tool for studies of diagnostic reliability (QAREL) tool (16 (Table 6) (34). Having two different operators also increased the variability (normal expected range, 1.39 IU/ml; 95% CI, 1.12-1.72) based on 42 comparisons in two studies (24,35). In addition, including a storage step for plasma (at 280 8 C or 4 8 C) contributed to an increase in variability: normal expected range, 60.66 IU/ml (95% CI, 0.61-0.72) if a sample was frozen at 280 8 C (done on 21 subjects) and 60.83 IU/ml (95% CI, 0.55-0.73) if a sample was kept at 4 8 C (done on 267 subjects) compared with fresh plasma processing ( Table 6).…”

“…A total of seven studies were included (6,(22)(23)(24)(25)(26)(27). Individual test data were available for five studies with a total of 739 subjects, with each subject providing two test results obtained in identical settings.…”