Answers

What an ESR (sed rate) blood test measures

A sed rate usually arrives as one number in mm/hr among your other lab results. Where it lands depends partly on the lab, your age and your sex, so it reads best next to the tests drawn with it.

Arun Verma, co-founder of Triangle · 2026-10-19

This is not clinical evidence and not medical advice. It does not replace your care team. Discuss anything here with your clinician before you act on it.

What is an ESR blood test?

An ESR, short for erythrocyte sedimentation rate, is a blood test that can show whether there is inflammation in your body. It measures how quickly your red blood cells settle to the bottom of a tall, thin tube. Inflammation makes red blood cells stick together in clumps, and the heavier clumps sink faster. Your report may call it a sed rate, a sedimentation rate or a Westergren sedimentation rate. The result is the height of clear plasma above the settled cells after one hour, so it is reported in millimeters per hour (mm/hr). The blood comes from a vein in your arm, and MedlinePlus says the ESR itself needs no special preparation.

What does an ESR tell you, and what can't it tell you?

It points to inflammation in general, not to a particular disease. Faster rates mean more inflammation, but an ESR alone cannot say which condition is causing it. MedlinePlus's encyclopedia says the test indirectly measures the level of certain proteins in the blood, and that the measurement correlates with the amount of inflammation in the body. StatPearls, a medical reference on the NIH's NCBI Bookshelf, describes the ESR as a physical measure of red blood cells clumping, shaped by proteins in the blood, rather than a direct test of a single inflammatory marker. The same chapter says the ESR lacks both sensitivity and specificity as a general screening tool.

Why would a rheumatologist order an ESR with other tests?

Because one number can't name a cause, an ESR is usually one test among several. It can be used with other tests to help diagnose and monitor conditions that cause inflammation, such as arthritis, vasculitis, infections and inflammatory bowel diseases, including Crohn's disease. It may also be used to keep an eye on a condition you already have. MedlinePlus's encyclopedia lists autoimmune disorders and certain forms of arthritis among the things it is useful for detecting and monitoring. In rheumatology it sits beside other evidence. The American College of Rheumatology (ACR) says diagnosing rheumatoid arthritis requires a physical exam, multiple blood tests and scans. Its giant cell arteritis fact sheet says the sed rate measures inflammation, but that finding alone is not proof of the disease. A C-reactive protein (CRP) test is often done at the same time to add information.

What is a normal ESR result?

It depends on your age, your sex and the lab, and the range printed on your own report comes first. StatPearls says the reference range should be set by the laboratory doing the test, and that ESR values are generally higher in women than in men and tend to rise with age. For the Westergren method, MedlinePlus's encyclopedia lists normal adult results as less than 15 mm/hr for men under 50, less than 20 for men over 50, less than 20 for women under 50 and less than 30 for women over 50. It adds that normal ranges may vary slightly among labs. StatPearls prints the same cutoffs as "or lower" rather than "less than", and says an abnormal ESR alone does not establish a diagnosis.

What else can raise or lower an ESR?

Quite a lot besides inflammation, which is one reason a single result isn't read alone. MedlinePlus says normal levels vary with age and sex, that factors such as aging, drinking alcohol regularly and exercise can affect results, and that certain medicines and supplements may too. Anemia can raise the rate as well. StatPearls lists anemia among additional factors that contribute to a higher ESR. MedlinePlus's encyclopedia says an increased rate may occur in people with anemia. Infections are among the causes of a high result, alongside inflammatory conditions such as giant cell arteritis, systemic vasculitis, polymyalgia rheumatica, and rheumatoid arthritis and other autoimmune diseases. How the sample is handled matters as well. StatPearls says a warm room, a tilted tube and vibration can push the value up. It also says delays in processing lower the ESR, and it puts the limit at 2 hours from collection.

Can you have inflammation and a normal ESR?

Yes. MedlinePlus says it's possible to have a condition that causes inflammation and still have a normal ESR result. In rheumatoid arthritis and lupus, StatPearls says the ESR is often used to support the diagnosis but does not always match clinical measures of disease activity. Some people with active rheumatoid arthritis, and inflammation seen in the joint lining under a microscope, still have a normal ESR. ACR's polymyalgia rheumatica fact sheet makes a similar point: not everyone with the condition has high inflammation markers, such as the sed rate, in their blood.

How do I compare ESR results from different offices or labs?

With care, because the number depends on the method and the lab as well as on you. StatPearls says the ESR can be measured by the Westergren, Wintrobe, micro-ESR or automated methods. Many automated analyzers calculate a rate from early red-cell clumping instead of measuring the settling directly. The chapter cites one study in which automated results differed from standard values by as much as 142%. It also says more recent studies find automated measurements closely track the Westergren method. With results from more than one practice, a fair question for whoever ordered each test is which method the lab used and which reference range it prints. StatPearls adds that a result outside the reference range is not necessarily a cause for concern, and that mild rises can come from factors such as laboratory variability or increasing age.

What could I ask about my ESR result?

You could ask what the ESR is being used for in your case, which other tests from the same draw it was read with, and how it compares with your earlier results from the same lab. Another fair question is whether anything around the draw, such as a delay before the sample was processed or a new medicine, might have affected it. MedlinePlus's encyclopedia points the meaning of your specific result back to your provider. No source says what a given ESR means for a given person; that is a question for the team that knows your history.

Sources

• MedlinePlus: Erythrocyte Sedimentation Rate (ESR) (last updated December 2, 2024): MedlinePlus says an erythrocyte sedimentation rate (ESR) is a blood test that can show if you have inflammation in your body, and that the test measures how quickly your red blood cells settle or sink to the bottom of a tall, thin test tube.
• MedlinePlus: Erythrocyte Sedimentation Rate (ESR) (last updated December 2, 2024): MedlinePlus says inflammation makes red blood cells stick together in clumps, and these clumps are heavier than single cells, so they sink faster.
• MedlinePlus: Erythrocyte Sedimentation Rate (ESR) (last updated December 2, 2024): MedlinePlus lists other names for the test: ESR, SED rate, sedimentation rate and Westergren sedimentation rate.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Specimen Requirements and Procedure): StatPearls says the result is based on the height of the plasma column, measured in millimeters after 1 hour, and is reported in millimeters per hour (mm/hr).
• MedlinePlus: Erythrocyte Sedimentation Rate (ESR) (last updated December 2, 2024): MedlinePlus says a health care professional takes a blood sample from a vein in your arm, using a small needle.
• MedlinePlus: Erythrocyte Sedimentation Rate (ESR) (last updated December 2, 2024): MedlinePlus says you don't need any special preparations for the ESR test, though you may need to fast if your provider ordered other tests on the same blood sample.
• MedlinePlus: Erythrocyte Sedimentation Rate (ESR) (last updated December 2, 2024): MedlinePlus says faster ESR rates mean higher levels of inflammation, but an ESR test alone cannot diagnose which condition is causing the inflammation.
• MedlinePlus Medical Encyclopedia: ESR (review date 7/1/2025): MedlinePlus's encyclopedia says the ESR indirectly measures the level of certain proteins in the blood, and that this measurement correlates with the amount of inflammation in the body.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Pathophysiology): StatPearls describes the ESR as a physical measure of red blood cell aggregation influenced by plasma protein interactions rather than a direct assay of a single inflammatory marker.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Clinical Significance): StatPearls says the ESR lacks both sensitivity and specificity as a general screening tool.
• MedlinePlus: Erythrocyte Sedimentation Rate (ESR) (last updated December 2, 2024): MedlinePlus says an ESR test can be used with other tests to help diagnose and monitor conditions that cause inflammation, including arthritis, vasculitis, infections and inflammatory bowel diseases (ulcerative colitis and Crohn's disease), and may also be used to monitor an existing condition.
• MedlinePlus Medical Encyclopedia: ESR (review date 7/1/2025): MedlinePlus's encyclopedia says the test is not used to diagnose a specific disorder but is useful for detecting and monitoring autoimmune disorders, bone infections, certain forms of arthritis and inflammatory diseases.
• American College of Rheumatology patient fact sheet: Rheumatoid Arthritis (updated February 2025): ACR says diagnosing rheumatoid arthritis requires a physical exam, multiple blood tests and scans like X-ray, MRI or ultrasound.
• American College of Rheumatology patient fact sheet: Giant Cell Arteritis (updated February 2025): ACR says there is no simple blood test to confirm the diagnosis of giant cell arteritis (GCA), and that the sed rate is a blood test that measures inflammation but that finding alone is not proof for GCA.
• MedlinePlus: Erythrocyte Sedimentation Rate (ESR) (last updated December 2, 2024): MedlinePlus says a C-reactive protein (CRP) test is commonly done with an ESR to provide more information.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Results, Reporting, and Critical Findings): StatPearls says the reference range for ESR should be established by the laboratory performing the test, and that ESR values are generally higher in female than in male individuals and tend to increase with age.
• MedlinePlus Medical Encyclopedia: ESR (review date 7/1/2025): MedlinePlus's encyclopedia lists normal adult results (Westergren method) as less than 15 mm/hr for men under 50, less than 20 mm/hr for men over 50, less than 20 mm/hr for women under 50 and less than 30 mm/hr for women over 50.
• MedlinePlus Medical Encyclopedia: ESR (review date 7/1/2025): MedlinePlus's encyclopedia says normal value ranges may vary slightly among different labs.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Results, Reporting, and Critical Findings): StatPearls gives Westergren reference values as 15 mm/hr or lower for men younger than 50, 20 mm/hr or lower for women younger than 50, 20 mm/hr or lower for men older than 50 and 30 mm/hr or lower for women older than 50.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Results, Reporting, and Critical Findings): StatPearls says reference ranges must be interpreted alongside clinical presentation and additional laboratory data, and that an abnormal ESR alone does not establish a diagnosis.
• MedlinePlus: Erythrocyte Sedimentation Rate (ESR) (last updated December 2, 2024): MedlinePlus says normal ESR levels vary depending on age and sex, that factors such as aging, drinking alcohol regularly and exercise can affect ESR results, and that certain medicines and supplements may also affect results.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Clinical Significance): StatPearls says additional contributing factors to an elevated ESR include anemia, RBC abnormalities, tilted ESR tubes, elevated specimen temperature, and dilution errors.
• MedlinePlus Medical Encyclopedia: ESR (review date 7/1/2025): MedlinePlus's encyclopedia says an increased ESR rate may occur in people with anemia.
• MedlinePlus: Erythrocyte Sedimentation Rate (ESR) (last updated December 2, 2024): MedlinePlus says a high ESR result may be from a condition that causes inflammation, such as giant cell arteritis, arthritis, systemic vasculitis, polymyalgia rheumatica, inflammatory bowel disease, infections, and rheumatoid arthritis and other autoimmune diseases.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Interfering Factors): StatPearls says elevated room temperature increases the ESR, and that tube tilt and vibration elevate the ESR value.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Interfering Factors): StatPearls says delays in processing the blood sample reduce the ESR, and that testing should be initiated within 2 hours of sample collection.
• MedlinePlus: Erythrocyte Sedimentation Rate (ESR) (last updated December 2, 2024): MedlinePlus says it's possible to have a condition that causes inflammation and still have a normal ESR result.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Clinical Significance): StatPearls says that in rheumatoid arthritis and systemic lupus erythematosus, ESR levels are frequently used to support the diagnosis, but ESR does not always correlate with clinical measures of disease activity.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Clinical Significance): StatPearls says some patients with active rheumatoid arthritis and histologic evidence of synovial inflammation may present with a normal ESR.
• American College of Rheumatology patient fact sheet: Polymyalgia Rheumatica (updated February 2025): ACR says a rheumatologist can do blood tests to look for unusually high markers of inflammation, like the erythrocyte sedimentation ("sed") rate and C-reactive protein, and that not everyone with polymyalgia rheumatica (PMR) has high levels of these in their blood.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Diagnostic Tests): StatPearls says ESR can be measured using the Westergren, Wintrobe, micro-ESR or automated method.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Diagnostic Tests): StatPearls says many automated analyzers do not measure sedimentation directly but instead calculate a derived rate based on early-stage red blood cell aggregation.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Diagnostic Tests): StatPearls says a study found that fewer laboratories now use the unmodified Westergren technique and that automated results may differ from standard values by as much as 142%.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Diagnostic Tests): StatPearls says recent studies demonstrate that automated ESR measurements closely correlate with those obtained using the Westergren method.
• StatPearls (NIH NCBI Bookshelf): Erythrocyte Sedimentation Rate, Tishkowski K, Zubair M, last update July 7, 2025 (Enhancing Healthcare Team Outcomes): StatPearls says a result outside the reference range is not necessarily a cause for concern, and that mild elevations may occur due to factors such as laboratory variability or increasing age.
• MedlinePlus Medical Encyclopedia: ESR (review date 7/1/2025): MedlinePlus's encyclopedia says to talk to your health care provider about the meaning of your specific test results.

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