The Erythrocyte Sedimentation Rate (ESR) test, also known as the sedimentation rate or “sed rate,” is a laboratory test used to assess the presence and severity of inflammation in the body. The test measures the rate at which red blood cells (erythrocytes) settle to the bottom of a vertical tube of blood over a specific period, usually one hour. Inflammatory proteins, such as fibrinogen and immunoglobulins, cause red blood cells to clump together, making them heavier and increasing their sedimentation rate. Therefore, an elevated ESR is indicative of increased inflammation, although it does not specify the cause or location of the inflammation. The ESR test is nonspecific and can be influenced by various factors, including age, sex, anemia, pregnancy, certain medications, and other medical conditions. Despite its lack of specificity, the ESR test is valuable in clinical practice as a screening tool for detecting inflammatory conditions, such as infections, autoimmune diseases, rheumatic disorders, malignancies, and tissue injuries.