A sedimentation rate blood test, also known as an erythrocyte sedimentation rate (ESR) or Westergren test, measures the rate at which red blood cells settle in a tube of blood. The ESR is a non-specific measure of inflammation and can be used to help diagnose conditions such as infection, autoimmune disorders, cancer, and pregnancy. The test is usually performed on a venous blood sample, drawn from a vein in the arm. The ESR is increased in conditions such as rheumatoid arthritis, lupus, and temporal arteritis. It can also be elevated in response to some medications such as aspirin.