Sedimentation rate (sed rate) is a type of blood test commonly used to screen for inflammation. It is a screening test and is not used to diagnose a specific disease or condition. Rather, sed rate, also called the erythrocyte sedimentation rate (ESR), is used along with other tests to help physicians determine what might be causing inflammation in the body. 

Sed rate is conducted by obtaining a blood sample from a patient’s vein, usually in the arm. From the blood sample, the rate that the blood cells fall (sedimentation) is measured in a test tube. As the red blood cells fall, plasma is left at the top of the test tube. Results of a sed rate test are recorded in terms of how many millimeters of clear plasma are left at the top of the tube per hour (mm/hr). An increased sed rate may be due to a higher level of certain proteins which can be caused by inflammation.

A sed rate test is useful because the result is  usually abnormal (positive) long before other biochemical or physical signs appear. High levels may indicate conditions such as a heart attack, rheumatic fever, giant cell arteritis, severe anemia or cancer relapse. Low levels may indicate conditions such as heart failure or sickle cell anemia.

Sed rates are generally used as a screening tool when assessing for disease, or to monitor the progress of chronic diseases such as Hodgkin's disease and other cancers. Regular sed rate testing can also provide an early warning of relapse in some patients.