An ESR blood test is a simple test that looks for signs of inflammation in the body. ESR stands for erythrocyte sedimentation rate. You may see it on a blood test report as “ESR”, “sed rate” or “erythrocyte sedimentation rate”.
ESR is often used when doctors are looking for inflammation, infection, autoimmune disease or certain long-term inflammatory conditions. It may be checked if you have symptoms such as unexplained tiredness, fever, weight loss, joint pain, muscle pain, headaches, stiffness, abdominal symptoms or ongoing illness that has not yet been explained.
However, ESR is a non-specific test. That means it can show that inflammation may be present, but it cannot tell you exactly where the inflammation is or what is causing it. A raised ESR does not diagnose a specific disease. A normal ESR does not always rule out a problem. The result has to be interpreted with your symptoms, examination findings and other blood tests such as CRP, full blood count, liver function, kidney function, thyroid tests and autoimmune markers.
This guide explains what ESR measures, what high and low results may mean, how ESR differs from CRP, why results can be raised for many reasons, and when you should speak to a GP or clinician.
Important: This article is for general information only and should not replace medical advice. If you have severe symptoms, unexplained weight loss, persistent fever, chest pain, severe headache, vision changes, black stools, blood in your stool, severe abdominal pain, shortness of breath or feel very unwell, seek medical advice promptly.
What is ESR?
ESR measures how quickly red blood cells settle at the bottom of a tall, thin tube over a set period, usually one hour. The result is reported in millimetres per hour, written as mm/hr.
When inflammation is present, certain proteins in the blood can increase. These proteins can make red blood cells clump together and fall more quickly. The faster the red blood cells settle, the higher the ESR result.
That sounds straightforward, but ESR is influenced by many things. Inflammation is one cause, but age, sex, pregnancy, anaemia, kidney disease, some infections, autoimmune conditions and some cancers can also affect the result. This is why ESR should not be interpreted as a standalone diagnosis.
NHS Inform describes ESR as a test that measures how long it takes red blood cells to fall to the bottom of a test tube, with faster settling making higher levels of inflammation more likely. You can read more in the NHS Inform guide to common blood tests.
Why might you have an ESR blood test?
A GP, hospital doctor or specialist may request ESR when they want to check for inflammation or monitor a known inflammatory condition.
You may have ESR tested if you have:
- unexplained fever
- ongoing tiredness or weakness
- unexplained weight loss
- joint pain, swelling or stiffness
- muscle aches or morning stiffness
- headaches, scalp tenderness or jaw pain in older adults
- symptoms that may suggest autoimmune disease
- ongoing abdominal symptoms
- suspected infection
- anaemia or abnormal full blood count results
- symptoms that have not been explained by initial tests
- a known inflammatory condition that needs monitoring
ESR is often requested alongside CRP. Both are inflammation markers, but they behave differently. CRP often rises and falls more quickly, while ESR can change more slowly and can remain raised for longer.
If you are trying to understand several blood results together, you may also find How to Understand Blood Test Results useful.
What does ESR measure?
ESR does not measure a specific chemical, antibody or infection. It measures the behaviour of red blood cells in a tube. Inflammation changes blood proteins, and those proteins can affect how quickly red blood cells settle.
This means ESR is an indirect marker. It tells you that something in the body may be increasing the tendency of red blood cells to settle faster. It does not tell you whether the cause is infection, autoimmune disease, tissue injury, cancer, anaemia, pregnancy or another factor.
Because of this, ESR is best understood as a clue. A useful clue, but still a clue.
What is a normal ESR result?
Normal ESR ranges vary between laboratories, and your result should always be compared with the reference range printed on your own report.
As a broad guide, ESR tends to be lower in younger adults and higher in older adults. It is also often slightly higher in women than men. Some laboratories use different age-adjusted ranges.
| Group | Common broad guide range | Important note |
|---|---|---|
| Men under 50 | Often below about 15 mm/hr | Ranges vary by lab. |
| Women under 50 | Often below about 20 mm/hr | Ranges vary by lab. |
| Men over 50 | Often below about 20 mm/hr | ESR can rise with age. |
| Women over 50 | Often below about 30 mm/hr | ESR can rise with age. |
| Children | Often lower than adult ranges | Interpretation depends on age and symptoms. |
These are only general guide values. Some NHS laboratories use their own local reference ranges. A result just above the reference range may not mean the same thing as a very high result.
What does a high ESR mean?
A high ESR means red blood cells settled faster than expected. This may suggest inflammation somewhere in the body, but it does not identify the cause.
Possible causes of a raised ESR include:
- infection
- inflammatory arthritis
- autoimmune disease
- polymyalgia rheumatica
- giant cell arteritis
- inflammatory bowel disease
- kidney disease
- anaemia
- some cancers
- pregnancy
- recent surgery, injury or tissue damage
- some long-term inflammatory conditions
A raised ESR is therefore not a diagnosis. It is a reason to look at the wider picture. Your GP or specialist will usually consider your symptoms, age, medical history and other test results.
If CRP is also raised, that may support the idea of active inflammation or infection. If ESR is raised but CRP is normal, the interpretation may be different and may depend on age, anaemia, kidney function, autoimmune history and whether symptoms are ongoing.
For more on another common inflammation marker, see CRP and Inflammation Blood Test Results Explained.
What does a mildly raised ESR mean?
A mildly raised ESR is common and can happen for many reasons. It may be related to a recent infection, mild inflammation, age, anaemia, pregnancy, weight, chronic health conditions or a result that is only slightly outside the laboratory range.
A small rise is usually interpreted differently from a very high ESR. For example, an ESR of 25 mm/hr in an older adult may be much less concerning than an ESR of 100 mm/hr in someone with fever, weight loss and night sweats.
If your ESR is only mildly raised and you feel well, your GP may choose to repeat it later or look at related tests such as CRP, full blood count, kidney function, liver function and urine tests.
If you have symptoms, the symptoms matter more than the number alone.
What does a very high ESR mean?
A very high ESR is more likely to need medical follow-up, especially if it is above 100 mm/hr or is rising over time. Very high ESR levels can be seen with significant infection, autoimmune or inflammatory disease, some cancers, kidney disease and other serious conditions.
That does not mean a very high ESR automatically means cancer or a dangerous diagnosis. It means the result should not be ignored.
If ESR is very high, a clinician may ask about:
- fever or night sweats
- unexplained weight loss
- new headaches or vision symptoms
- joint pain or swelling
- muscle pain and morning stiffness
- cough, urinary symptoms or signs of infection
- abdominal pain, diarrhoea or blood in stool
- bone pain
- fatigue or symptoms of anaemia
- changes in kidney or liver blood tests
Further tests may include full blood count, CRP, kidney and liver tests, urine tests, chest X-ray, stool tests, autoimmune tests, scans or specialist referral depending on symptoms.
Can ESR be normal when something is wrong?
Yes. A normal ESR does not rule out every condition.
Some infections, inflammatory conditions or cancers may not raise ESR, especially early on or in mild disease. Some conditions raise CRP more clearly than ESR. Some symptoms may come from problems that are not inflammatory at all.
If your ESR is normal but symptoms continue, worsen or feel unusual for you, go back to your GP. A normal ESR should not be used to dismiss persistent symptoms such as weight loss, ongoing fever, blood in stool, severe fatigue, unexplained pain or new neurological symptoms.
Can ESR be low?
A low ESR is usually not a concern. Many healthy people have a low ESR. It often simply means there is no obvious ESR pattern suggesting inflammation.
Occasionally, a very low ESR may be seen with conditions that affect red blood cells or blood proteins, such as polycythaemia, some red cell shape disorders or very high white blood cell counts. These are not usually diagnosed from ESR alone.
If your ESR is low but other blood tests are abnormal, your GP will interpret the full pattern rather than focusing on ESR alone.
ESR vs CRP: what is the difference?
ESR and CRP are both inflammation markers, but they are not the same.
CRP, or C-reactive protein, is a protein made by the liver in response to inflammation. It often rises quickly during infection or inflammation and can fall quickly when the problem improves.
ESR measures how quickly red blood cells settle in a tube. It often changes more slowly and can be affected by more non-inflammatory factors, such as age, sex, pregnancy and anaemia.
| Feature | ESR | CRP |
|---|---|---|
| What it measures | How fast red blood cells settle | A liver-made inflammation protein |
| Speed of change | Usually changes more slowly | Often rises and falls faster |
| Affected by age and anaemia | More affected | Less affected |
| Useful for | Some chronic inflammatory conditions and monitoring | Acute inflammation, infection and treatment response |
| Can diagnose a condition alone? | No | No |
Patient.info notes that ESR and plasma viscosity do not change as rapidly as CRP at the start or end of inflammation, and that CRP is affected by fewer other factors. You can read more in its guide to blood tests used to detect inflammation.
What if ESR is high but CRP is normal?
Sometimes ESR is raised while CRP is normal. This can happen because ESR is affected by more factors than CRP.
Possible explanations include:
- older age
- anaemia
- pregnancy
- kidney disease
- some autoimmune conditions
- past inflammation that is settling
- certain blood protein changes
- a mild or non-specific result
It can also happen in some inflammatory conditions, so it should not be dismissed automatically. The meaning depends on symptoms and other results.
If ESR is raised but CRP is normal and you feel well, your GP may simply repeat the test or check for anaemia and other causes. If you have symptoms such as weight loss, persistent fever, headaches, joint swelling or severe fatigue, further assessment may be needed.
What if CRP is high but ESR is normal?
CRP can rise quickly in acute infection or inflammation, while ESR may remain normal early on. This pattern can happen when inflammation is recent or short-lived.
For example, a bacterial infection may cause a clear rise in CRP before ESR changes much. CRP may also fall faster with treatment, while ESR can remain raised longer.
A high CRP with normal ESR should be interpreted with symptoms. If you have fever, pain, shortness of breath, urinary symptoms, abdominal pain or feel very unwell, the CRP may be more important than the ESR.
Can anaemia raise ESR?
Yes. Anaemia can raise ESR, even when inflammation is not the main issue. This is one reason ESR is often interpreted alongside a full blood count.
If you have a raised ESR and low haemoglobin, your GP may look for causes of anaemia such as iron deficiency, B12 or folate deficiency, chronic disease, heavy periods, gut blood loss or kidney disease.
Useful related guides include Full Blood Count Results Explained, Iron, Ferritin and Anaemia Blood Test Results Explained and B12 and Folate Blood Test Results Explained.
Can infection raise ESR?
Yes. ESR can be raised by infections, especially if they are significant, persistent or slow to resolve. This may include chest infections, urinary infections, bone infections, endocarditis, tuberculosis, abdominal infections and other causes.
However, ESR is not specific enough to tell where an infection is. A clinician will look at symptoms, examination findings, temperature, CRP, full blood count, urine tests, cultures, imaging or other investigations.
If you have fever, chills, severe pain, confusion, shortness of breath, signs of sepsis or feel seriously unwell, seek urgent medical help rather than waiting for blood test interpretation.
Can autoimmune disease raise ESR?
Yes. ESR can be raised in autoimmune and inflammatory diseases, including rheumatoid arthritis, lupus, vasculitis, polymyalgia rheumatica and giant cell arteritis.
In these conditions, ESR may be used alongside symptoms, examination, CRP, full blood count, kidney tests, urine tests and specialist antibody tests.
Symptoms that may suggest an inflammatory or autoimmune condition include:
- persistent joint swelling
- morning stiffness lasting more than 30 to 60 minutes
- unexplained rashes
- mouth ulcers with other systemic symptoms
- Raynaud’s symptoms
- unexplained fever
- chest pain on breathing
- blood or protein in urine
- muscle pain and stiffness in older adults
If symptoms are persistent or worsening, ask your GP whether further autoimmune or rheumatology assessment is needed.
ESR, polymyalgia rheumatica and giant cell arteritis
ESR is particularly associated with two inflammatory conditions: polymyalgia rheumatica and giant cell arteritis.
Polymyalgia rheumatica, often shortened to PMR, usually affects people over 50. It can cause pain and stiffness around the shoulders, neck, hips and thighs, often worse in the morning.
Giant cell arteritis, also called temporal arteritis, is a serious condition involving inflammation of blood vessels, usually in older adults. It can cause new headaches, scalp tenderness, jaw pain when chewing, vision symptoms and general illness. It can threaten sight and needs urgent medical attention.
The NHS says ESR and CRP are blood tests that can be used to check inflammation levels in suspected polymyalgia rheumatica, and that if both are normal, PMR is unlikely. You can read more on the NHS polymyalgia rheumatica diagnosis page.
If you are over 50 and develop a new severe headache, scalp tenderness, jaw pain when chewing, visual disturbance or sudden vision loss, seek urgent medical help.
Can inflammatory bowel disease raise ESR?
Yes. ESR may be raised in inflammatory bowel disease, including Crohn’s disease and ulcerative colitis, especially during active inflammation. CRP, full blood count, albumin, liver tests, stool calprotectin, colonoscopy and imaging may also be used.
Symptoms that may suggest inflammatory bowel disease include:
- persistent diarrhoea
- blood or mucus in stool
- abdominal pain
- unexplained weight loss
- fatigue
- anaemia
- night-time bowel symptoms
If digestive symptoms are part of the picture, see Inflammatory Bowel Disease: Crohn’s Disease vs Ulcerative Colitis Explained, Blood in Stool and Coeliac Blood Test Results Explained.
Can cancer raise ESR?
Some cancers can raise ESR, but ESR is not a cancer test. A raised ESR alone does not mean you have cancer, and many people with raised ESR do not have cancer.
However, an unexplained raised ESR may need follow-up if it occurs with symptoms such as unexplained weight loss, persistent fever, night sweats, blood in stool, persistent pain, a new lump, unexplained anaemia, loss of appetite or ongoing fatigue.
Research using UK primary care data has found that raised inflammatory markers such as ESR, CRP and plasma viscosity can be associated with increased cancer risk in some age groups, but the tests are not sensitive or specific enough to be used alone. This means they can contribute to the overall picture but cannot rule cancer in or out by themselves.
If you have persistent unexplained symptoms, speak to a GP even if ESR is only mildly raised or other tests are normal.
Can kidney disease raise ESR?
Yes. Kidney disease can be associated with a raised ESR. This may be due to inflammation, anaemia, changes in blood proteins or the kidney condition itself.
If ESR is raised and kidney blood tests are abnormal, your GP may look at creatinine, eGFR, urine protein, blood pressure, diabetes status and medication history.
Related guides include Kidney Blood Test Results Explained, eGFR and Creatinine Results Explained and U&E Blood Test Results Explained.
Can pregnancy raise ESR?
Yes. ESR often rises during pregnancy. This is one reason ESR is harder to interpret during pregnancy and after childbirth.
If you are pregnant and your ESR is raised, your clinician will usually interpret it with symptoms and other tests rather than treating the ESR alone as a sign of disease.
Can age affect ESR?
Yes. ESR tends to increase with age. This means a result that looks slightly raised in a younger adult may be interpreted differently from the same result in an older adult.
Age does not mean raised ESR should always be ignored. It simply means context matters. A new raised ESR in an older adult with weight loss, headaches, anaemia, pain or fever needs more attention than a stable, mildly raised ESR in someone who feels well and has no concerning symptoms.
Can medicines affect ESR?
Some medicines can indirectly affect ESR by treating or causing inflammation, changing blood counts, affecting proteins or influencing the underlying condition being monitored.
For example, steroids used to treat inflammatory conditions may reduce ESR over time. Some treatments for autoimmune disease may also lower ESR as inflammation improves. On the other hand, medicines that cause anaemia or trigger inflammation may affect the wider picture.
Always tell your clinician what medicines, supplements and over-the-counter products you take. Do not stop prescribed medicine based only on an ESR result.
What other tests are usually checked with ESR?
ESR is often most useful when combined with other tests. These may include:
- CRP — another inflammation marker
- Full blood count — checks anaemia, white cells and platelets
- Liver function tests — checks liver enzymes and proteins
- Kidney function tests — checks creatinine, eGFR and urea/electrolytes
- Ferritin and iron studies — checks iron stores and inflammation-related patterns
- Thyroid function tests — checks for thyroid disease when symptoms overlap
- Urine tests — checks infection, blood or protein
- Autoimmune tests — such as ANA, rheumatoid factor, anti-CCP or ANCA when clinically indicated
- Stool tests — if bowel inflammation or infection is suspected
- Imaging — such as X-ray, ultrasound, CT or MRI depending on symptoms
Useful related guides include Liver Function Test Results Explained, Thyroid Blood Test Results Explained and Urine Test Results Explained.
What if your ESR was tested privately?
ESR is sometimes included in private health checks, inflammation panels or blood test packages. If your ESR is abnormal on a private test, do not panic, but do not ignore it either.
Ask:
- How high is the ESR compared with the reference range?
- Was CRP also checked?
- Was full blood count checked?
- Do I have symptoms that could explain the result?
- Have I recently had an infection, injury, surgery or flare-up of a known condition?
- Could anaemia, pregnancy, kidney disease or age affect the result?
- Should the test be repeated?
- Do I need GP review?
If ESR is very high, rising, unexplained or linked with symptoms, share the full report with your GP. Include the date of the test, all related results and why the test was done.
For a broader guide, see What to Do After Abnormal Private Blood Test Results.
Should ESR be repeated?
Sometimes. Repeating ESR can be useful if the result is mildly raised, unexpected, or being used to monitor a known inflammatory condition.
A repeat test may show whether ESR is:
- returning to normal after infection or inflammation
- remaining stable
- rising over time
- falling after treatment
- linked with another abnormal result such as CRP or anaemia
However, repeating ESR is not always the right first step. If symptoms are concerning, a clinician may arrange further investigations rather than simply waiting for another ESR result.
How quickly does ESR change?
ESR usually changes more slowly than CRP. It may rise more gradually and remain raised after inflammation has started to improve. This can be useful in some long-term inflammatory conditions, but it can also make ESR less helpful for very acute changes.
If a doctor wants to know whether an infection or inflammation is changing quickly, CRP may be more useful. If they are monitoring a condition such as polymyalgia rheumatica, giant cell arteritis or some rheumatology conditions, ESR may still provide helpful information.
Can lifestyle changes lower ESR?
There is no specific “ESR-lowering diet” that should be used instead of diagnosis or treatment. ESR usually improves when the underlying cause improves.
If ESR is raised because of an infection, autoimmune disease, inflammatory bowel disease, anaemia or another medical condition, the correct treatment depends on that cause.
General health measures may support overall wellbeing, such as:
- not smoking
- limiting alcohol
- maintaining a balanced diet
- treating iron deficiency or vitamin deficiency if confirmed
- managing long-term conditions such as diabetes or kidney disease
- keeping up with prescribed medication
- seeking help for persistent symptoms rather than self-treating blindly
But do not focus only on lowering the ESR number. The important question is why it is raised.
When should you contact a GP about ESR?
You should contact a GP or clinician if:
- your ESR is above the reference range and you do not know why
- your ESR is very high
- your ESR is rising over time
- you have persistent fever or night sweats
- you have unexplained weight loss
- you have ongoing fatigue with anaemia or other abnormal results
- you have new joint swelling or morning stiffness
- you have muscle pain and stiffness, especially over age 50
- you have persistent abdominal symptoms or blood in stool
- you have headaches, scalp tenderness or jaw pain over age 50
- your private ESR result is abnormal and you are unsure what to do next
Seek urgent help if you have severe symptoms such as chest pain, severe shortness of breath, signs of stroke, sudden vision loss, severe headache with scalp tenderness, severe abdominal pain, confusion, collapse or signs of sepsis.
How to read ESR results step by step
If you have your ESR result in front of you, use this order:
- Check the number and unit. ESR is usually reported in mm/hr.
- Compare with the laboratory range. Ranges vary by age, sex and laboratory.
- Look at how raised it is. Mildly raised and very high results are interpreted differently.
- Check CRP. CRP may show more acute inflammation.
- Check full blood count. Anaemia can raise ESR and may be a clue.
- Look at symptoms. Fever, weight loss, pain, stiffness, bowel symptoms and headaches matter.
- Consider recent illness or injury. Infection, surgery or inflammation may explain a temporary rise.
- Look for trends. Is ESR rising, falling or stable?
- Ask what the next step is. You may need repeat testing, related blood tests, imaging or specialist review.
The bottom line
ESR is a useful blood test for detecting or monitoring inflammation, but it is not specific. A raised ESR does not tell you exactly what is wrong, and a normal ESR does not rule out every condition.
ESR is best interpreted with symptoms and other tests, especially CRP and full blood count. It can be raised by infection, autoimmune disease, inflammatory bowel disease, polymyalgia rheumatica, giant cell arteritis, anaemia, kidney disease, pregnancy, age and some cancers.
If your ESR is mildly raised and you feel well, your GP may repeat it or check related tests. If it is very high, persistent, rising or linked with symptoms such as fever, weight loss, night sweats, headaches, joint swelling or blood in stool, it needs proper medical review.
The aim is not simply to “lower ESR”. The aim is to understand why it is raised and whether anything needs treatment.
Frequently asked questions
What does ESR stand for?
ESR stands for erythrocyte sedimentation rate. It measures how quickly red blood cells settle at the bottom of a test tube over a set time.
What does an ESR blood test show?
ESR can show that inflammation may be present in the body. It does not show where the inflammation is or what is causing it.
What is a normal ESR?
Normal ESR ranges vary by laboratory, age and sex. It is usually reported in mm/hr. Always compare your result with the reference range on your own report.
What does a high ESR mean?
A high ESR may suggest inflammation, infection, autoimmune disease, anaemia, kidney disease, pregnancy or other conditions. It needs interpretation with symptoms and other tests.
Does high ESR mean cancer?
No. High ESR does not automatically mean cancer. Many non-cancer conditions can raise ESR. However, unexplained raised ESR with symptoms such as weight loss, night sweats, persistent fever or anaemia should be reviewed by a GP.
Can ESR be high after an infection?
Yes. ESR can remain raised for a while after infection or inflammation and may fall more slowly than CRP.
Can anaemia raise ESR?
Yes. Anaemia can raise ESR. This is why ESR is often interpreted alongside a full blood count.
Can pregnancy raise ESR?
Yes. ESR often rises during pregnancy, so it can be harder to interpret in pregnancy.
Can age affect ESR?
Yes. ESR tends to increase with age. A mildly raised ESR may be interpreted differently in older adults than in younger adults.
What is the difference between ESR and CRP?
CRP often rises and falls more quickly during inflammation. ESR changes more slowly and is affected by more factors such as age, sex, pregnancy and anaemia.
Which is better, ESR or CRP?
Neither is always better. CRP is often more useful for acute inflammation, while ESR can still be useful in some chronic inflammatory conditions and monitoring situations.
Can ESR be normal when CRP is high?
Yes. CRP can rise quickly in acute inflammation or infection before ESR changes much.
Can ESR be high when CRP is normal?
Yes. ESR can be raised by age, anaemia, pregnancy, kidney disease, some autoimmune conditions and other factors even when CRP is normal.
What does a very high ESR mean?
A very high ESR may suggest significant inflammation, infection, autoimmune disease, kidney disease or other serious causes. It should be reviewed by a clinician, especially if symptoms are present.
Is low ESR bad?
Usually not. A low ESR is commonly normal and not a concern unless other blood tests or symptoms suggest a specific problem.
Do I need to fast before an ESR blood test?
Usually no. ESR itself does not normally require fasting, but other tests taken at the same time may have different instructions.
Can ESR diagnose rheumatoid arthritis?
No. ESR can support the picture if inflammation is present, but rheumatoid arthritis diagnosis also depends on symptoms, examination, other blood tests and sometimes imaging.
Can ESR diagnose polymyalgia rheumatica?
No single test diagnoses polymyalgia rheumatica, but ESR and CRP are often used to support diagnosis and monitor inflammation.
Should I worry about a mildly raised ESR?
Not always. A mildly raised ESR may be temporary or non-specific. It should be interpreted with symptoms, age, CRP, full blood count and other results.
What should I do after an abnormal ESR result?
Ask why the test was done, how abnormal it is, whether CRP and full blood count are normal, whether it should be repeated, and whether your symptoms need further investigation.
