Sedimentation rate, also called erythrocyte sedimentation rate (ESR) or sed rate, is a type of blood test used to identify the presence of inflammation somewhere in the body. The test measures the rate at which red blood cells (erythrocytes) separate from blood plasma, the liquid component of blood in which blood cells are suspended.

Sed rate blood tests are not used to diagnose a specific disease or condition, but rather serve as a screening tool for many different conditions and diseases, including:

• Cancers, including blood cancers 
  

• Infections
  
  
• Autoimmune disorders such as rheumatoid arthritis and lupus

Patients need to take very few preparatory steps prior to a sed rate blood test, but are advised to follow any instructions provided by their physician. Sed rate blood tests are quick, simple and relatively inexpensive. They pose few risks, and most people who undergo them experience only slight to moderate pain or discomfort.

During a sed rate test, blood is drawn from a patient’s vein and placed in a test tube. 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.