Comparison between ELISA and automated ECLIA for Interleukin-6 determination during COVID-19 pandemic

ABSTRACT

Background: The severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2) is a highly contagious illness associated with a hyperactivated and dysregulated host immune humoral response. In detail, there is a cytokine storm which may take to the release of interleukin IL-6 as a critical mediator for respiratory failure, shock and multiorgan dysfunction. Such dysregulation may act as a target for therapeutics and, in this view, a blockade of IL-6 function by an anti-IL-6 receptor antibody (tocilizumab) has been described to be effective for the treatment of the inflammatory process COVID-19-related. Timing of administration of therapy was reported in literature to have a critical role in benefit for patients;thus, the aim of the present study is to compare two different methods for the IL-6 assessment the Human IL-6 ELISA Kit (Invitrogen) and the Elecsys IL-6 (Roche). Method(s) IL-6 levels of 128 COVID-19 patients, who were consequently admitted to the Emergency and Medicine Department of AOU Careggi (Hospital in Florence -Italy ) between April and May 2020, were assessed by using the two above mentioned methods and were analysed through Passing-Bablok regression fit and Bland-Altman plot. Result(s) The analyses showed that the two methods correlate, but do not agree in terms of numeric results. In particular, further investigation were performed on the Bland-Altman results, showing that the maximum number of samples for which the differences between the two methods is close to "0" (p > 0.05) (which means a good overlap between the two methods) is 49 (p=0.07), and among them, 40 samples showed a complete agreement of results (p=0.95). These results can be attributed to the different methods' linearities 3.1-200 pg/mL for ELISA and 1.5#5000 pg/mL for ECLIA, which could be extended to 50 000 pg/mL. Conclusion(s) Although a small percentage of data overlapping in a certain range, still a high correlation among the two methods can be found;given the overall analytical performance of the ECLIA, it can be considered more adequate for different reasons i) it is available on a fully automated platform h24, ii) it uses of a small sample volume, iii) it is low cost and no-time consuming and iiii) the different timing for measuring IL-6 is much attractive.