Short-term Reproducibility of a Commercial Interferon-gamma Release Assay. - Related Articles
Short-term Reproducibility of a Commercial Interferon-gamma Release Assay.
Clin Vaccine Immunol. 2009 Jun 17;
Authors: Detjen AK, Loebenberg L, Grewal HM, Stanley K, Gutschmidt A, Kruger C, Du PN, Kidd M, Beyers N, Walzl G, Hesseling AC
Background. Interferon-gamma (IFN-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 on the reproducibility and within-person variability of these assays. Objectives. Various aspects of short-term reproducibility of a commercial IGRA, the QuantiFERON-TB(R) Gold In-Tube (QFT-IT) were assessed. Design. QFT-IT 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 one, and one set on day 3. Aspects such as inter-operator, intra-operator, day-to-day variability, test-retest variability as well as different storage methods of plasma were investigated. Results. Seventeen of 27 (63%) of participants had at least one positive QFT-IT; 6 had discordant results. The agreement of all aspects studied was high with kappa values between 0.82 to 1.00 for dichotomous, and inter class correlations (ICC) of 0.809 to 0.965 observed for continuous IFN-gamma measures. The variability of the magnitude of response was highest comparing measures obtained from individuals on different days (ICC 0.809). The magnitude of IFN-gamma response in individual participants ranged from 0.03 to 11 IU/ml, resulting in discordant results in 5 participants. Conclusions. QFT-IT is a robust and highly reproducible assay. Considerable intra-individual variability occurs in the magnitude of IFN-gamma responses, which may influence the interpretation of serial measures.
PMID: 19535542 [PubMed - as supplied by publisher] [Tuberculosis Pulmonary]