Sed rate (erythrocyte sedimentation rate)

Sed rate, or erythrocyte sedimentation rate (ESR), is a blood test that can reveal inflammatory activity in your body. A sed rate test isn't a stand-alone diagnostic tool, but it may help your doctor diagnose or monitor the progress of an inflammatory disease.

When your blood is placed in a tall, thin tube, red blood cells (erythrocytes) gradually settle to the bottom. Inflammation can cause the cells to clump together. Because these clumps of cells are denser than individual cells, they settle to the bottom more quickly.

The sed rate test measures the distance red blood cells fall in a test tube in one hour. The farther the red blood cells have descended, the greater the inflammatory response of your immune system.

Why it's done How you prepare What you can expect Results

Sed rate tests were used more frequently in the past than they are today because more-specific measures of inflammatory activity are now available. Today, the test is most often used if your doctor suspects you have:

  • Giant cell arteritis
  • Polymyalgia rheumatica
  • Rheumatoid arthritis

A sed rate test can also help determine the severity of your inflammatory response and monitor the effect of treatment.

Because a sed rate test can't pinpoint the problem that's causing inflammation in your body, it's usually accompanied by other blood tests, such as the C-reactive protein (CRP) test.

© 1998-2015 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved. Terms of use