Interleukin 6

Function

Interleukin 6 (IL-6) is a versatile pro-inflammatory cytokine produced by various cells, including T-cells, macrophages, and endothelial cells. It plays a pivotal role in the body's acute phase response, acting as a messenger that signals the liver to produce C-reactive protein (CRP) and fibrinogen. IL-6 is involved in the transition from acute inflammation to chronic inflammation and is a key driver of B-cell differentiation into antibody-producing plasma cells. While essential for fighting infections and healing injuries, chronic overproduction of IL-6 can lead to tissue destruction and systemic disease.

Why it is Ordered

IL-6 testing is frequently used to assess the severity of systemic inflammation. In recent years, it became a critical biomarker for identifying 'cytokine storm' in severe COVID-19 patients, helping clinicians decide when to use IL-6 inhibitors like tocilizumab. It is also used in rheumatology to monitor disease activity in rheumatoid arthritis and systemic juvenile idiopathic arthritis. Other indications include the evaluation of patients with suspected Castleman disease, sepsis, or localized infections that have become systemic.

Associated Conditions

• Rheumatoid Arthritis (RA): High IL-6 levels contribute to joint destruction and systemic symptoms like fatigue.
• Sepsis: IL-6 is an early marker of the systemic inflammatory response syndrome (SIRS).
• Cytokine Release Syndrome (CRS): Often seen after CAR-T cell therapy or severe viral infections.
• Castleman Disease: A rare lymphoproliferative disorder driven by excessive IL-6.
• Chronic Stress and Obesity: Both conditions are associated with low-grade, chronic elevations of IL-6.