Sedimentation rate is a type of 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 sed rate test does not diagnose disorders, but serves as a screening tool that may indicate several diseases and conditions, including those which affect the skin. Such conditions include hives, systemic lupus erythematosus, psoriatic arthritis and Raynaud’s phenomenon (discoloration of the fingers and toes caused by cold or stress that is frequently seen in scleroderma patients).

Sed rate tests are interpreted based on what they reveal about the body’s 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. During the test, blood is drawn from a patient’s vein 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 a disease and the effectiveness of medical treatment.