Evaluation of an automated immunoassay method for cytokine measurement using the Immulite (R) immunoassay system

Cytokines are key mediators in cell regulation and communication. The conce ntration of these proteins can rapidly and importantly increase during seve re clinical situations. However, current techniques are not adapted to stat measurement, thus making their clinical use limited. In this context, the commercialization of five new kits for cytokine measur ement interleukin ((IL)-1, IL-6, IL-8, tumor necrosis factor (TNF)-alpha an d IL-2R) on an automated immunoanalyzer, the Immulite(R), seems to be a new approach for the determination of these markers. We report here the evalua tion of the performance of these tests. The technique is based on a solid p hase (bead) two site chemiluminescent enzyme immunometric assay. The analys is is performed within 60 to 90 minutes and the calibration is stable for 1 5 days. The values of the between-run imprecision study were similar to those from the within-run study with coefficients of variation (CV) ranging from 2% (l ow values of IL-8) to 11.5 % for intermediate concentrations of IL-6 (500 p g/ml). CVs were usually around 5 %. The accuracy was determined by a linearity study using standards (except fo r IL-2R) provided by the National Institute for biological Standards and Co ntrol (NIBSC). Slopes obtained during this study were close to 1 (r(2) = 0. 99), except for IL-6, for which the slope was 1.55. TNF-alpha values were c lose to those expected. IL-1 results were about 20 % higher. IL-6 values we re over estimated above 100 pg/ml and under estimated below this value. IL- 8 study seemed to be impaired by the poor stability of this molecule in the NIBSC preparation. Correlation study with standard laboratory techniques g ave variable results : for IL-1 (n = 43) the slope was 0.77 (study carried out using cell culture media), for IL-6 (n = 54) the slope was 0.78, for IL -8 (n = 37) the slope was 1.64, for TNF-alpha (n = 40) the slope was 0.33 a nd the slope for IL-2R (n = 51) was 5.1. For the last cytokine, the unit in Immulite assay was different from the one used in our comparison technique . Cross-calibration results were consistent with these data and show that t he bias is probably linked to a calibration problem. The study demonstrated excellent practicality of the system, and good stabi lity of the calibration curve (15 days). However, the sample volume require d (350 mu l for the IL-6 and the TNF-alpha) could constitute a limitation f or pediatric measurements.