The erythrocyte seimentation rate (ESR), also called a sedimentation rate, sed rate, or Biernacki Reaction, is the rate at which red blood cells precipitate in a period of 1 hour. It's a common haematology test which is a non-specific measure of inflammation. To perform the test, anticoagulated blood is placed in an upright tube, known as a Westergren tube and the rate at which the red blood cells fall is measured and reported in mm/h.