Interleukin-6 (IL-6) is a pleiotropic cytokine that plays a crucial role in both pro-inflammatory and anti-inflammatory responses, acting as a key mediator of the immune system. This test measures IL-6 levels in the blood to assess inflammatory status and disease severity. IL-6 is involved in acute phase responses, fever induction, immune cell differentiation, and tissue repair. Elevated IL-6 levels indicate increased inflammation and are associated with various conditions including severe infections, autoimmune diseases, and cytokine release syndrome. The test is particularly valuable for evaluating patients with severe COVID-19, as IL-6 levels above 35 pg/mL may predict the need for mechanical ventilation. IL-6 measurements help guide treatment decisions, monitor inflammatory response, and assess prognosis in patients with severe inflammatory conditions.