Interleukin-6: A Versatile Biomarker in the Clinical Chemistry Laboratory in the COVID-19 Era

Interleukin-6 (IL-6) is a proinflammatory cytokine released during the cytokine storm of sepsis and Coronavirus Disease-2019 (COVID-19). IL-6 has been extensively used as a biomarker in Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2) and in the emerging novel paediatric disease called Paediatric Inflammatory Multisystem Syndrome-temporarily associated with SARS-CoV-2 (PIMS-TS) or Multisystem Inflammatory Syndrome in Children (MIS-C). Additionally, IL-6 measurement is necessary to decide for several cytokine-blocking and cytokine-removal therapies and to determine treatment adequacy. Aim: Evaluation of the performance of IL-6 in COVID-19, PIMS-TS/MIS-C and in CytoSorb cytokine removal therapy in sepsis as a versatile biomarker in clinical chemistry laboratory. Materials and Methods: The study was an exploratory descriptive study carried out between March 2019 and February 2021 for a period of 24 months. IL-6 (pg/mL) was measured on Roche e411 immunoassay platform using Electrochemiluminiscence Assays (ECLIA) in 15 adult patients. Biological reference interval of the parameter was <7 pg/mL. Results: The results showed that IL-6 was increased significantly in non survivors compared to survivors with COVID-19 (p-value=0.0043). IL-6 levels (normal <7 pg/mL) were highly elevated in children with PIMS-TS {median 75.9 pg/mL (IQR: 47.3-223.4)} reflecting the intense inflammatory state of the novel paediatric condition. All PIMS-TS cases (n=13) survived. IL-6 levels were increased post CytoSorb therapy in sepsis patients who did not survive and declined in survivors. IL-6 serially measured during treatment helped to monitor therapeutic adequacy in prolonged sepsis case. Conclusion: The various applications of automated IL-6 testing in the clinical chemistry laboratory reflects the versatility of the trending biomarker.