New quantitative electrochemiluminescence method (ECLIA) for interleukin-6 (IL-6) measurement

Background: A new interleukin-6 (IL-6) electrochemiluminescent immunoassay (ECLIA, Roche Diagnostics) was evaluated and compared to a previous semiquantitative immunoassay (Milenia Biotec). Reference ranges for cord blood plasma were also calculated. Methods: The new IL-6 ECLIA test was performed using a Cobas E601 analyzer (Roche Diagnostics). The comparison method (Milenia Biotec) was a semiquantitative lateral flow immunoassay, coupled to a digital image capture system (PicoScan). Healthy at term newborns were recruited to establish reference ranges for IL-6 in cord blood plasma. Results: Total imprecision ranged from 3.7% to 8.0% depending on the IL-6 concentrations. The calculated limit of detection for IL-6 measured by ECLIA was 2.63 pg/mL, almost twice as high as that claimed by the manufacturer (1.5 pg/mL). The linearity of the method was verified to 5000 pg/mL. The IL-6 reference limit, obtained from 148 cord blood samples, was 30 pg/mL (90% confidence interval: 19–48 pg/mL). Conclusions: The new quantitative ECLIA method showed good reproducibility, linearity and functional sensitivity. Additional clinically based studies are needed to elucidate the usefulness of the IL-6 reference limit, calculated here for the first time by ECLIA in cord blood plasma, to aid in the diagnosis of vertical transmission of sepsis. Clin Chem Lab Med 2010;48:835–8.