If your doctor suspects high levels of inflammation in the body, they may recommend a blood test called an erythrocyte sedimentation rate (ESR) test. It looks at how quickly red blood cells may sink to the bottom of a test tube, with a high rate of settlement indicating high inflammation.

Also called a sedimentation rate test or sed rate test, an ESR test doesn’t diagnose one specific condition. Instead, it helps your doctor determine whether you’re experiencing inflammation and what further testing may be needed. The ESR test can also be used to monitor inflammatory diseases you already have.

Learn more about the ESR test, what the results could mean, and what information you may wish to discuss with your doctor before getting your blood drawn.

An ESR test measures the rate at which your red blood cells (RBCs) fall to the bottom of a test tube. The blood sample for this test is measured over the course of an hour.

When you’re experiencing inflammation, it can affect your RBCs in a number of ways. First, your RBCs cling together, forming clumps. This clumping affects the rate at which RBCs sink inside a tube where a blood sample is placed.

Also, if you have an acute infection or chronic inflammation, there may be more proteins in your RBCs. This can cause them to settle quicker. The faster and further the cells sink toward the bottom of a test tube, the more likely it is that inflammation is present.

In all, your ESR number is based on the rate that your RBCs settle. The faster this happens, the higher your ESR — and the more inflammation is likely in your body.

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

Also, if you already have an inflammatory condition, your doctor may order an ESR test as part of your routine lab work to make sure your current treatment plan is working.

Diagnosing conditions that cause inflammation

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

Monitoring inflammatory conditions

The ESR test can help a healthcare professional monitor autoimmune 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 medications. They may ask you to temporarily stop taking it before the test.

Certain medications may affect ESR test results. For example, steroids, nonsteroidal anti-inflammatory drugs (NSAIDs), and statins may cause possible false lower ESRs. However, you should not stop taking any prescription medications unless your doctor instructs otherwise.

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 is covered to stop any bleeding.

The blood sample is taken to a lab, where your blood will be placed in a long, thin tube in which it sits for one hour. During and after this hour, the laboratory professional processing this test 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.

Other tests that may be performed at the same time

Your doctor may order a C-reactive protein (CRP) test at the same time as your ESR test. CRP tests measure inflammation as well, but they can also help predict your risk of coronary artery disease (CAD) and other cardiovascular diseases.

Additionally, your doctor may order a complete blood count (CBC) test to look for other signs of inflammation or infection.

How long before results?

While wait times can vary, results from most labs done in a doctor’s office or a clinic take a few business days. Your doctor or nurse will call you with your results, along with any next steps.

There aren’t any risks directly associated with an ESR Test. However, having your blood drawn may involve 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. Talk with your doctor or lab technician about these concerns before you get your blood drawn.

There are two methods for measuring your erythrocyte sedimentation rate.

Westergren method

This is the most common ESR method. In this type of test, your 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 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. Overall, females naturally have higher ESR levels.

Normal ESR test results are as follows:

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

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

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

An abnormally low value would be near 0. It’s hard to state an exact value because these tests fluctuate, and what is ultimately considered too low may vary from one person to the next.

This test isn’t always reliable or meaningful. Many factors can affect 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 a higher rate 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 tests can potentially help your doctor figure out the specific cause of your inflammation.

If you have an underlying condition that’s causing high ESR levels, ESR tests can also be used to monitor your ESR levels during treatment to measure how well the treatments are working.

An underlying condition

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 the condition.

Inflammation

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

Infection

If a bacterial infection is causing your inflammation, your doctor will likely prescribe an antibiotic to fight this infection.

An ESR test is a type of blood test that your doctor may order to help measure inflammation in your body. It’s often done with other types of lab tests to rule out or diagnose a variety of inflammatory conditions.

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

A wide variety of acute and chronic conditions may affect your ESR levels, from autoimmune and cardiovascular diseases, to infections and certain cancers.

Talk with your doctor if you’re experiencing any symptoms you’re concerned about. They may recommend an ESR test based on your health history, symptoms, and physical exam.