Erythrocyte Sedimentation Rate (ESR)
The erythrocyte sedimentation rate (ESR) is a blood test that measures how quickly red blood cells settle in a test tube to detect inflammation in the body.
What is an erythrocyte sedimentation rate (ESR)?
Erythrocytes are red blood cells. The ESR test measures the time it takes for these cells to settle at the bottom of a test tube. Inflammation causes red blood cells to clump together, making them heavier and causing them to sink faster than normal. A faster ESR rate indicates a higher level of inflammation, though the test cannot identify the specific cause of that inflammation.
What is it used for?
The ESR test is used alongside other diagnostics to help identify and monitor conditions that cause inflammation, such as:
- Arthritis
- Vasculitis
- Infections
- Inflammatory bowel diseases (ulcerative colitis and Crohn's disease)
Why do I need an ESR?
Your provider may order an ESR if you have symptoms of inflammation, including:
- Headaches
- Unexplained fever or weight loss
- Joint stiffness
- Neck or shoulder pain
- Loss of appetite
- Anemia
What happens during an ESR?
A health care professional will take a blood sample from a vein in your arm using a small needle. The procedure typically takes less than five minutes. No special preparation is required, though you should inform your provider of any medications or supplements you are taking, as these can affect results.
What do the results mean?
High ESR results indicate that red blood cells sank faster than normal, which may be linked to conditions like giant cell arteritis, rheumatoid arthritis, systemic vasculitis, kidney disease, or certain cancers. Low ESR results indicate cells sank slower than normal, which may be associated with blood disorders (such as polycythemia or sickle cell disease), heart failure, or liver problems.
Because many factors—including age, sex, pregnancy, and obesity—can influence ESR levels, the test is rarely used in isolation. Providers often pair it with a C-reactive protein (CRP) test to gain a clearer picture of your health.