An erythrocyte sedimentation rate (ESR) test is sometimes called a sedimentation rate test or sed rate test. This blood test doesn’t diagnose one specific condition. Instead, it helps your doctor determine whether you’re experiencing inflammation.

The doctor will look at ESR results along with other information or test results to help figure out a diagnosis. The tests ordered will depend on your symptoms.

The ESR test can also be used to monitor inflammatory diseases.

When you’re experiencing inflammation, your red blood cells (RBCs) cling together, forming clumps. This clumping affects the rate at which RBCs sink in a tube of blood.

The test lets your doctor see how much clumping is occurring. The faster the cells sink to the bottom of a test tube, the more likely it is that inflammation is present.

The test can identify and measure inflammation in your body. However, it doesn’t help pinpoint the cause of inflammation. That’s why the ESR test is rarely performed alone. Instead, your doctor will combine it with other tests to determine the cause of your symptoms.

The ESR test can be used to help your doctor diagnose conditions that cause inflammation, such as:

The ESR test can help your doctor monitor inflammatory conditions, such as:

Your doctor might also order this test if you have:

You might need an ESR test if you experience symptoms of inflammatory conditions such as arthritis or inflammatory bowel disease (IBD). These symptoms can include:

The ESR test requires little preparation.

However, you should tell your doctor if you’re taking any medication. They may ask you to temporarily stop taking it before the test.

Many different medications and drugs affect ESR test results.

Medications and drugs that can cause abnormally high test results include:

Medications and drugs that can cause abnormally low test results include:

This test involves a simple blood draw. It should take only a minute or two.

  1. First, the skin directly over your vein is cleaned.
  2. Then, a needle is inserted to collect your blood.
  3. After collecting your blood, the needle is removed and the puncture site covered to stop any bleeding.

The blood sample is placed in a thin tube in which it sits for one hour. During and after this hour, your doctor will assess how far the RBCs sink into the tube, how quickly they sink, and how many sink.

Inflammation can cause abnormal proteins to appear in your blood. These proteins cause your RBCs to clump together. This makes them fall more quickly.

Your doctor may order a C-reactive protein (CRP) test at the same time as your ESR test. CRP measures inflammation as well, but it can also help predict your risk for coronary artery disease (CAD) and other heart disease.

Having your blood drawn involves minimal risks. Possible complications include:

You’ll probably feel mild to moderate pain when the needle pricks your skin. You might also feel throbbing at the puncture site after the test.

If you’re uncomfortable at the sight of blood, you may also experience discomfort seeing blood drawn from your body.

Your doctor will use one of two methods to measure your erythrocyte sedimentation rate.

Westergren method

In this method, your doctor will draw your blood into a Westergren-Katz tube until the blood level reaches 200 millimeters (mm).

The tube will be stored vertically and sit at room temperature for an hour.

Your doctor will measure the distance between the top of the blood mixture and the top of the sedimentation of RBCs.

Wintrobe method

The Wintrobe method is similar to the Westergren method, except the tube used is 100 mm long and thinner.

An advantage of this method is that it’s less sensitive than the Westergren method, so less blood is used.

ESR test results are measured in millimeters per hour (mm/hr).

The following are considered normal ESR test results:

  • Women under age 50 should have an ESR under 20 mm/hr.
  • Men under age 50 should have an ESR under 15 mm/hr.
  • Women over age 50 should have an ESR under 30 mm/hr.
  • Men over age 50 should have an ESR under 20 mm/hr.
  • Children should have an ESR between 0 and 10 mm/hr.

The higher the number, the higher the level of inflammation.

An abnormal ESR result doesn’t diagnose any particular disease. It just identifies any inflammation in your body and indicates a need to look further.

An abnormally low value would be near 0. (Because these tests fluctuate, it’s hard to state an exact value.)

This test isn’t always reliable or meaningful. Many factors can alter your results, such as:

Some causes of abnormal ESR test results are more serious than others, but many aren’t a huge concern. It’s important not to worry too much if your ESR test results are abnormal.

Instead, work with your doctor to find out what’s causing your symptoms. They’ll usually order follow-up tests if your ESR results are too high or low.

There are multiple causes of a high ESR test result. Some common conditions associated with high rates include:

An abnormally high ESR can indicate the presence of cancerous tumors, especially if no inflammation is found.

Autoimmune diseases

ESR test results that are higher than normal are also associated with autoimmune diseases, including:

Infections

Some types of infection that cause ESR test results to become higher than normal are:

A low ESR test result may be due to:

Depending on your results, your doctor may want to order additional tests, including a second ESR test to verify the results of the first one. These further tests can help your doctor identify the specific cause of your inflammation.

If you have a condition that falls into one of the categories below, further tests can also help measure the effectiveness of treatments and keep track of your ESR throughout your course of treatment.

An underlying condition

If your doctor suspects that an underlying condition is causing your high ESR, they may refer you to a specialist who can properly diagnose and treat the condition.

Inflammation

If your doctor detects inflammation, they may recommend one or more of the following treatments:

Infection

If an infection is causing your inflammation, your doctor will likely prescribe antibiotics to fight the infection.