Differential absolute plasma IL-6 concentrations between two immunoassay platforms in intensive care unit patients with COVID-19.

Abstract

Objectives: Explorewhether plasma IL-6 levels are similar across biomarker platforms and association with COVID-19 clinical outcomes. Methods: Plasma IL-6 concentrations were measured on 191 COVID-19 patients using the Roche Elecsys IL-6 assay and the Meso Scale Discoveryassay. Results: Correlation of IL-6 levels between platforms was high (r=0.87;95% CI: 0.82-0.89); however, agreement was low (bias: 147.2pg/ml; 95% limits of agreement: -489.5-783.9pg/ml). The optimal IL-6 threshold to predict invasive mechanical ventilation and in-hospital mortality were 3- and 3.4-fold higher in Roche compared with Meso Scale Discovery, respectively. Conclusion: The absolute IL-6 threshold to predict outcomes was consistently higher using the Roche platform, and IL-6 thresholds to inform prognosis vary based on the biomarker platform.