The sedimentation rate test measures inflammation in the body. It is also called the sed rate or the erythrocyte sedimentation rate (ESR) test. It is a blood test. It determines how quickly red blood cells sink in a tube of blood. The sedimentation rate test is used to diagnose, or to assess the progress of, inflammatory diseases, such arthritis and polymyalgia rheumatica, and autoimmune disorders, such as lupus.