An ESR test measures inflammation levels in the body. Doctors may use it and other tests to diagnose an inflammatory condition or monitor an existing condition, such as arthritis.

An erythrocyte sedimentation rate (ESR) test, also called a sedimentation rate test or sed rate test, measures how quickly red blood cells sink to the bottom of a test tube. A high rate of settlement indicates high levels of inflammation.

Rather than help diagnose a specific condition, an ESR test helps determine whether you’re experiencing inflammation and what further testing may be needed. It can also monitor inflammatory diseases.

Keep reading to learn more about the ESR test and what the results could mean.

An ESR test measures the rate at which your red blood cells (RBCs) fall to the bottom of a test tube over the course of an hour. The faster and further the cells sink toward the bottom of a test tube, the more likely inflammation is present.

Inflammation can affect RBCs in various ways:

  • Inflammation can cause RBCs to clump together, which affects the rate at which they sink inside a tube containing a blood sample.
  • An acute infection or chronic inflammation may increase the certain proteins in and around your RBCs, causing them to clump and settle quickly.

The ESR number is based on the rate at which your RBCs settle. The faster this happens, the higher your ESR and the more inflammation likely in your body.

An ESR test doesn’t help pinpoint the precise cause of inflammation. A doctor typically orders an ESR test and other tests to diagnose an inflammatory health condition.

If you already have an inflammatory condition, your doctor may order an ESR test as part of your routine lab work to monitor the effectiveness of your current treatment plan.

Diagnosing conditions that cause inflammation

Doctors may order an ESR test along with other tests to help diagnose conditions that cause inflammation, such as:

Monitoring inflammatory conditions

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

Your doctor might also order this test if you have:

The ESR test requires little preparation.

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

Some medications may affect ESR test results. These can include:

However, do not stop taking any prescription medication unless your doctor instructs you to do so. Stopping some prescription medications abruptly can cause serious side effects.

This test involves a simple blood draw. It typically takes 1 to 2 minutes.

The blood sample is then taken to a lab and placed in a long, thin tube for one hour.

Your doctor may order additional tests at the same time as your ESR test. These may include:

While wait times can vary, results from most labs done in a doctor’s office or a clinic take a few business days. Your healthcare professional may contact you to communicate the results or discuss them in an appointment, along with the next steps. You may also be able to see your results through an online portal.

There aren’t any risks directly associated with an ESR test. However, having your blood drawn may involve minimal risks, such as bleeding, bruising, or tenderness where the needle was inserted.

Talk with a doctor or lab technician about any concerns before you get your blood drawn.

There are two main methods for measuring your erythrocyte sedimentation rate. Some hospitals may also use automated methods that measure clumping rather than segmentation.

Westergren method

This is the most common ESR method. In this test, blood is drawn into a Westergren-Katz tube until the blood level reaches 200 millimeters (mm).

The tube is stored vertically and sits at room temperature for an hour. The distance between the top of the blood mixture and the top of the sedimentation of RBCs is measured.

Wintrobe-Landsberg method

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

A disadvantage of this method is that it’s less sensitive than the Westergren method.

ESR test results are measured in millimeters per hour (mm/hr). The higher the number, the higher the likelihood of inflammation.

ESR test results are as follows:

Normal ESR test resultsAbnormal ESR test results
Females under 50between 0 and 20 mm/hrgreater than 20
Males under 50between 0 and 15 mm/hrgreater than 15
Females over 50between 0 and 30 mm/hrgreater than 30
Males over 50between 0 and 20 mm/hrgreater than 20
Childrenbetween 0 and 10 mm/hrgreater than 10

An abnormal ESR result identifies potential inflammation in your body. Many factors can affect your results, such as:

  • older age
  • medication use
  • pregnancy
  • menstruation

A doctor usually orders follow-up tests if your ESR results are too high or low.

Various health issues can cause a high ESR test result. These may include:

An abnormally high ESR can result from cancerous tumors, especially if no inflammation is found.

ESR test results that are higher than 100 mm/hr could indicate a more “active” disease, such as cancer and vasculitis.

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 first one’s results. These tests can potentially help diagnose the cause of your inflammation.

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

If you already have a diagnosed underlying condition that causes high ESR levels, ESR tests can help monitor the effectiveness of the treatments.

An ESR test is a type of blood test that measures inflammation in the body. Doctors may order it along with other lab tests to rule out or diagnose various inflammatory conditions.

Depending on the results, a doctor may order more testing or refer you to a specialist, such as a rheumatologist.

Various acute and chronic conditions, from autoimmune and cardiovascular diseases to infections and certain cancers, may affect ESR levels.