erythrocyte sedimentation rate (ESR), the rate at which red blood cells settle out in a vertical column of anticoagulated whole blood, expressed in millimeters per hour. Blood is collected in an anticoagulant and allowed to form a sediment in a calibrated glass column. At the end of 1 hour the laboratory technician measures the distance the erythrocytes have fallen in the tube. Elevated sedimentation rates are not specific for any disorder but most commonly indicate the presence of inflammation. Inflammation causes an alteration of the blood proteins, which makes the red blood cells aggregate, becoming heavier than normal. The speed with which they fall to the bottom of the tube corresponds to the degree of inflammation. Serial evaluations of erythrocyte sedimentation rate are useful in monitoring the course of inflammatory activity in rheumatic diseases and, when performed with a white blood cell count, can indicate infection. Certain noninflammatory conditions, such as pregnancy, are also characterized by high sedimentation rates. The Westergren ESR is determined with a 200-mm Westergren tube. Values are higher for women in both methods and vary according to the method used. Normal findings by the Westergren method are up to 20 mm/hr for females and up to 15 mm/hr for males. Other diseases that alter blood proteins can also cause abnormal ESRs. Also called sedimentation rate. See also inflammation.
