Erythrocyte Sedimentation Rate (ESR)

What is an erythrocyte sedimentation rate (ESR)?

Erythrocytes are red blood cells. The sedimentation rate is the time it takes for your red blood cells to settle at the bottom of a test tube. An erythrocyte sedimentation rate (ESR) is a blood test that can show if you have inflammation in your body. Inflammation is your immune system's response to injury, infection, and many other conditions, including immune system disorders, certain cancers, and blood disorders.

To do an ESR test, a sample of your blood is sent to a lab. A health care professional places the sample in a tall, thin test tube and measures how quickly your red blood cells settle or sink to the bottom of the tube. Typically, red blood cells sink slowly. But inflammation makes red blood cells stick together in clumps. These clumps of cells are heavier than single cells, so they sink faster.

If an ESR test shows that your red blood cells sink faster than expected, it may mean you have a medical condition causing inflammation. How quickly the red blood cells in your sample fall to the bottom of the test tube is a sign of how much inflammation you have. Faster ESR rates mean higher levels of inflammation. But an ESR test alone cannot diagnose which condition is causing the inflammation.

Other names: ESR, SED rate sedimentation rate; Westergren sedimentation rate

What is it used for?

An ESR test can be used with other tests to help diagnose and monitor conditions that cause inflammation. Many conditions cause inflammation, including arthritis, vasculitis, infections, and inflammatory bowel diseases (ulcerative colitis and Crohn's disease). An ESR may also be used to monitor an existing condition.

Why do I need an ESR?

Your health care provider may order an ESR if you have symptoms of a condition that causes inflammation. Your symptoms will depend on the condition you may have, but they may include:

• Headaches
• Unexplained fever
• Unexplained 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. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for an ESR?

You don't need any special preparations for this test. But if your provider ordered other tests on your blood sample, you may need to fast (not eat or drink) for several hours before the test. Your provider will let you know if there are any special instructions to follow.

Are there any risks to the test?

There is very little risk to having an ESR. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Your provider will use your ESR test results, medical history, symptoms, and other test results to make a diagnosis. An ESR test alone cannot diagnose conditions that cause inflammation.

A high ESR test result means your red blood cells sank faster than normal. This may be from a condition that causes inflammation, such as:

• Giant cell arteritis, inflammation (swelling) of your arteries, usually in your scalp, neck, and arms
• Arthritis
• Systemic vasculitis, inflammation of your blood vessel walls, which can affect any of your organs
• Polymyalgia rheumatica
• Inflammatory bowel disease
• Kidney disease
• Infections
• Rheumatoid arthritis and other autoimmune diseases
• Heart disease
• Certain cancers

A low ESR test result means your red blood cells sank slower than normal. This may be caused by conditions such as:

• A blood disorder, such as:
  • Polycythemia, an increase in your red blood cells, which causes your blood to thicken
  • Sickle cell disease (SCD)
  • Leukocytosis, a very high white blood cell count (WBC)
• Heart failure
• Certain kidney and liver problems

If your ESR results are not normal, it doesn't always mean you have a medical condition that needs treatment. Normal ESR levels will vary, depending on your age and sex. Also, pregnancy, your menstrual cycle, aging, obesity, drinking alcohol regularly, and exercise can affect ESR results.  Certain medicines and supplements may also affect your results, so be sure to tell your provider about any medicines or supplements you are taking.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about an ESR?

Because an ESR can't diagnose a specific disease, your provider may order other tests at the same time. Also, it's possible to have a condition that causes inflammation and still have a normal ESR result. A C-reactive protein (CRP) test is commonly done with an ESR to provide more information.