Sedimentation rate is a blood test used to detect inflammation. The test, also called erythrocyte sedimentation rate (ESR) or sed rate, measures the rate at which red blood cells (erythrocytes) separate from blood serum in a patient’s blood sample.

The sedimentation rate test does not diagnose disorders. Rather, it serves as a screening tool that may indicate several conditions, including inflammatory diseases (e.g., rheumatoid arthritis, lupus), heart attack, infections, certain cancers and sickle cell anemia.

Sed rate tests are interpreted based on what they reveal about blood cells. Inflammation changes the amount of proteins in the blood, causing blood cells to clump together and form sediment faster than they normally would.

Blood is drawn from a patient and placed in a test tube for laboratory analysis. After one hour, the distance traveled by red blood cells toward the bottom of the tube is measured in millimeters, revealing how long it takes the cells to settle.  

The more red blood cells that accumulate at the bottom of the test tube in sediment layer, the higher the level of proteins present. The liver and the immune system produce these proteins when the body has certain conditions. In addition to helping in diagnosis, sed rate tests can be used to monitor the course of the disease and the effectiveness of medical treatment.