Testing

What an ESR Blood Test Shows and What Results Mean

Medically reviewed by Medical Advisory Board Last reviewed 2026-10-06

An erythrocyte sedimentation rate measures inflammation by tracking how fast red blood cells settle

An ESR blood test measures erythrocyte sedimentation rate to detect inflammation in your body. It checks how quickly red blood cells settle in a test tube, though it cannot diagnose a specific disease on its own. Review your lab report against facility reference ranges and discuss follow-up testing with your doctor.

An erythrocyte sedimentation rate (ESR) blood test measures how fast red blood cells settle in a test tube to show whether you have inflammation in your body. At The Metabolic Journal, we summarize what MedlinePlus reports about how this test evaluates inflammation across different clinical conditions.

Also known as a sed rate test or sedimentation rate, this test tracks the settling speed of erythrocytes, which is the medical term for red blood cells. You may see it listed on a lab order next to other tests, for example if you came here from the hypothyroidism guide or a thyroid panel. Because an ESR test alone cannot identify the specific illness causing inflammation, healthcare providers use it together with your symptoms, medical history, and other test results.

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What an ESR Blood Test Measures

An ESR blood test measures how quickly red blood cells settle at the bottom of a tall, thin test tube to determine if inflammation is present in your body. Erythrocytes are red blood cells, and the sedimentation rate reflects the time it takes for these cells to sink. The test also goes by the names sed rate, sedimentation rate, and Westergren sedimentation rate.

Under typical conditions, red blood cells sink slowly. Inflammation causes red blood cells to stick together in clumps, which are heavier than single cells and sink much faster. A faster sedimentation rate indicates higher levels of inflammation in your blood.

An ESR blood test alone cannot diagnose which specific condition is causing the inflammation. Instead, healthcare providers use it alongside other diagnostic tools to help diagnose and monitor conditions that cause inflammation. These include arthritis, vasculitis, infections, and inflammatory bowel diseases such as ulcerative colitis and Crohn's disease.

Symptoms That Prompt an ESR Blood Test

A healthcare provider may order an ESR blood test if you develop symptoms associated with an inflammatory condition. Because inflammation can affect multiple body systems, the physical signs prompting a sed rate test vary widely.

According to MedlinePlus, common symptoms that lead clinicians to order an ESR include:

Headaches
Unexplained fever
Unexplained weight loss
Joint stiffness
Neck or shoulder pain
Loss of appetite
Anemia

Because these symptoms can stem from many different ailments, providers use the sedimentation rate to confirm the presence of inflammation rather than identify a single cause.

How the Sed Rate Test Is Performed and How to Prepare

An ESR blood test is a routine procedure that takes less than five minutes to complete. A healthcare professional draws a sample of blood from a vein in your arm. The sample is sent to a laboratory, where a technician places the blood in a tall, thin test tube and measures how quickly the red blood cells settle to the bottom.

The blood draw carries very little risk. You may experience slight pain or minor bruising where the needle entered your skin, but these symptoms typically go away quickly.

No special preparation is required for a standalone ESR blood test. If your healthcare provider ordered other blood tests on the same sample, you may need to fast for several hours before the draw. Your provider will give you specific instructions if fasting is necessary.

What a High ESR Blood Test Result Means

A high ESR blood test result means your red blood cells settled faster than normal, which may point to a condition that causes inflammation.

A high sedimentation rate can result from several conditions that cause inflammation:

Giant cell arteritis
Polymyalgia rheumatica
Systemic vasculitis
Arthritis, including rheumatoid arthritis and other autoimmune diseases
Inflammatory bowel disease, such as Crohn's disease and ulcerative colitis
Infections
Kidney disease
Heart disease
Certain cancers

Because an elevated rate cannot point to a single diagnosis, your doctor will evaluate these possibilities against your physical symptoms and other laboratory tests.

What a Low ESR Blood Test Result Means

A low ESR blood test result means your red blood cells settled more slowly than normal toward the bottom of the tube.

Conditions that may cause a low sedimentation rate include:

Blood disorders, such as polycythemia and sickle cell disease
Leukocytosis, which involves a very high white blood cell count
Heart failure
Certain kidney problems
Certain liver problems

Your provider will use your medical history, symptoms, and other test results to interpret a low result.

Factors That Influence Results and the Role of ESR vs CRP

An abnormal ESR blood test result does not always mean you have a medical condition requiring treatment. Normal ESR levels vary naturally by age and sex, so use the reference range printed on your lab report.

Several everyday factors, physiological states, and habits can alter your sedimentation rate:

Aging
Pregnancy
Your menstrual cycle
Obesity
Drinking alcohol regularly
Exercise
Certain prescription medicines and dietary supplements

Tell your healthcare provider about every medicine and supplement you take so they can interpret your results accurately.

It is also possible to have an inflammatory condition and still have a normal ESR result. A C-reactive protein (CRP) test is commonly done together with an ESR to provide more information. Review your complete laboratory panel with your doctor to determine your next diagnostic steps.

Where to Find Blood Panel Test Kits

Many labs and direct-to-consumer services let you order a blood panel test without a doctor's visit. If you'd rather compare kits yourself, here's where to start looking:

At-home blood panel test kits on Amazon — compare brands, prices, and Prime shipping.

Frequently Asked Questions

What is a sed rate test?

A sed rate test, also called an erythrocyte sedimentation rate (ESR) test, is a blood test that measures how quickly red blood cells settle at the bottom of a test tube. Faster settling signals inflammation in your body, because inflammation makes red blood cells clump together and sink faster. The test alone cannot diagnose a specific disease, so clinicians use it with other evaluations.

What does a high ESR mean?

A high ESR means your red blood cells settled faster than normal, which indicates that inflammation is present in your body. This elevated rate can stem from infections, kidney disease, heart disease, certain cancers, or autoimmune conditions like rheumatoid arthritis, polymyalgia rheumatica, and inflammatory bowel disease. Because an ESR alone cannot diagnose the cause, your provider may use other tests to find it.

What does a low ESR mean?

A low ESR means your red blood cells settled more slowly than normal. This slower rate can be caused by conditions such as heart failure, leukocytosis (a very high white blood cell count), certain liver or kidney problems, or blood disorders like sickle cell disease and polycythemia. Your provider will interpret it alongside your symptoms and other tests.

Do I need to fast for an ESR test?

You do not need to fast for an ESR blood test if it is ordered on its own. However, if your doctor orders additional lab tests using the same blood sample, you may need to fast for several hours before the draw. Always check with your healthcare provider for specific instructions before your appointment.

Can ESR be normal if I have inflammation?

Yes, it is possible to have an inflammatory condition and still receive a normal ESR blood test result. A C-reactive protein (CRP) test is commonly done together with an ESR to provide more information.

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Medical Disclaimer: This content is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before making changes to your health regimen.

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