If you have been asked to take a blood sedimentation test, or you have received an ESR result in a blood report and want to understand what it means, this guide explains the science behind the test, how results are interpreted, and what to do if your result falls outside the expected range.
Blood sedimentation is a term that refers most commonly to the erythrocyte sedimentation rate (ESR) — a simple, widely used laboratory measurement that can give healthcare professionals a useful indication of inflammation in the body. It is not a diagnostic test in isolation, but it plays a meaningful role as part of a broader clinical picture.
What Is Blood Sedimentation?
Blood sedimentation refers to the rate at which red blood cells (erythrocytes) settle to the bottom of a vertical tube of blood over a set period, typically one hour. This settling process is measured and recorded as the erythrocyte sedimentation rate, or ESR.
Under normal circumstances, red blood cells have a slight negative electrical charge that causes them to repel one another, which means they settle relatively slowly. When inflammation is present in the body, certain proteins — particularly fibrinogen and immunoglobulins — accumulate in the blood and cause red blood cells to clump together. These clumps, sometimes called rouleaux formations, are heavier and settle faster, producing a higher ESR reading.
The term red blood cell sedimentation rate (RBC sedimentation rate) is used interchangeably with ESR in clinical practice. Both describe the same measurement.
What Is an ESR Blood Test Used For?
The ESR blood test is one of the oldest and most established laboratory investigations in medicine. It is a non-specific marker of inflammation, which means an elevated result signals that inflammation may be present somewhere in the body, but does not pinpoint where it is, what is causing it, or how severe it is.
Clinicians may request an ESR blood test for several reasons, including:
It is important to understand that ESR alone cannot diagnose infection, autoimmune disease, cancer or any other condition. A healthcare professional will always interpret the result alongside your symptoms, medical history and other test findings.
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How Is the Blood Sedimentation Test Performed?
The blood sedimentation test requires a standard blood sample, usually taken from a vein in the arm. The process is straightforward and takes only a few minutes.
Once the sample is collected, it is sent to a laboratory, where the Westergren method is most commonly used. In this technique, blood is diluted with sodium citrate solution and placed in a long, thin, calibrated tube. The tube is held vertically and the distance (in millimetres) that red blood cells settle over one hour is measured. This measurement — expressed in millimetres per hour (mm/hr) — is the ESR result.
The Westergren method is considered the international standard for ESR measurement and is the technique referenced in most published reference ranges.
There is no special preparation required for an ESR test in most circumstances, though your healthcare provider may advise you about any specific requirements depending on other tests being taken at the same time.
Blood Sedimentation Rate Normal Range
One of the most commonly searched questions about this test is: *what is the normal blood sedimentation rate?*
The answer is that reference ranges vary depending on several factors, including the laboratory method used, the patient's age and sex. There is no single universal threshold.
As a general guide, many UK laboratories use the Westergren method and apply broadly similar reference intervals. Commonly cited ranges include:
These figures are illustrative and reflect values commonly referenced in UK clinical guidance. They should not be treated as absolute thresholds. Your laboratory report will include its own reference interval, and this should always be used when interpreting your result.
Results that fall slightly above the upper limit of a reference range in an otherwise healthy individual may have different significance than a substantially elevated result in someone with symptoms. Context is everything.
What Does a High Blood Sedimentation Rate Mean?
A high blood sedimentation rate — also referred to as an elevated ESR — indicates that red blood cells are settling more quickly than expected, which may suggest increased levels of certain proteins associated with inflammation.
Common causes associated with a high ESR include:
It is essential to emphasise that a high ESR is not a diagnosis. Many people with a mildly elevated ESR have no significant underlying condition. The result must always be considered together with other clinical information. A healthcare professional is the appropriate person to help you understand what an elevated result means in your individual situation.
What Does a Low Blood Sedimentation Rate Mean?
A low blood sedimentation rate is generally of limited clinical concern in the majority of contexts. An ESR that falls below the lower end of the laboratory reference interval is less commonly a focus of clinical investigation than a high result.
In some circumstances, a very low ESR may be associated with:
A low result should still be discussed with a healthcare professional if it is unexpected or accompanied by symptoms. As with a high result, interpretation depends on the full clinical picture.
Factors That Can Affect ESR Results
Because ESR is influenced by multiple physiological and technical variables, healthcare professionals are trained to interpret it with care. Several factors can raise or lower the result independently of true inflammation:
Factors that may raise ESR:
Factors that may lower ESR:
Factors that may affect reliability:
These variables are one reason why ESR is rarely used as a standalone test. Understanding the individual context is crucial when interpreting any ESR result.
ESR in a Blood Report
When you receive a blood report containing an ESR result, the reading will typically be expressed as a number followed by mm/hr (millimetres per hour). For example, a result of 22 mm/hr means that red blood cells settled 22 millimetres in one hour under test conditions.
Alongside your numerical result, the report will include a laboratory reference interval — the range considered normal for your age and sex by that particular laboratory. Your result should be interpreted against this interval rather than any general figure you may find online.
Key points when reading an ESR result in a blood report:
If you have received an abnormal ESR result and are uncertain what it means, speaking with a qualified healthcare professional is the most appropriate next step.
ESR Compared With Other Blood Tests
The ESR is one of several blood tests used to investigate or monitor inflammation. Understanding how it compares to other commonly used tests can help put your results in context.
ESR vs CRP (C-reactive protein)
CRP is a protein produced by the liver in response to inflammation. It is considered a more specific and sensitive marker of acute inflammation than ESR because it rises and falls more rapidly in response to changes in inflammatory activity.
Because of these different response times, the two tests can complement each other. They are not interchangeable and each provides different clinical information.
ESR vs Full Blood Count
A full blood count provides detailed information about red blood cells, white blood cells and platelets. It can help identify anaemia, infection or blood disorders that may explain an abnormal ESR. Healthcare professionals frequently request ESR alongside a full blood count to build a more complete picture.
Neither test replaces the other. Together, they can provide complementary information that helps guide further investigation.
How to Reduce a High Blood Sedimentation Rate
This is one of the most common questions people ask after receiving an elevated ESR result. The honest answer is that you cannot meaningfully reduce your ESR by targeting the number itself. ESR is a marker — treating the marker without addressing the underlying cause is not a clinically appropriate approach.
If your ESR is elevated, the correct focus is on:
1. Identifying the underlying cause through further investigation with a healthcare professional
2. Receiving appropriate treatment for any confirmed condition, which may then result in ESR returning towards a normal range as inflammation is controlled
3. Supporting general health through evidence-based lifestyle measures, which may support wellbeing but should not be presented as a guaranteed method of reducing ESR
Do not start or stop any medication, supplement or treatment in response to a blood test result without first discussing it with a qualified healthcare professional. Self-managing an unexplained elevated ESR without appropriate medical assessment is not advisable.
When to Seek Medical Advice
An abnormal ESR result on its own does not automatically mean something serious is wrong. However, there are circumstances where you should seek medical advice promptly:
Speak to a healthcare professional if:
Seek urgent care if:
If you are considering private blood testing to investigate symptoms or check your ESR alongside other markers, you can explore available blood tests or book an appointment with Private Blood Tests London. For broader health assessment, a health screening package may provide a more comprehensive overview alongside your ESR result.
Private blood testing can provide timely access to results, but it complements rather than replaces NHS care and professional medical assessment.
Frequently Asked Questions
What does blood sedimentation rate mean?
Blood sedimentation rate refers to the erythrocyte sedimentation rate (ESR) — a measurement of how quickly red blood cells settle in a tube of blood over one hour. A faster rate may indicate the presence of inflammation or other changes in blood protein levels.
What is an ESR blood test?
An ESR (erythrocyte sedimentation rate) blood test measures how rapidly red blood cells settle in a sample of blood. It is a non-specific marker used to help investigate or monitor inflammation, and is usually performed using the Westergren method.
What is the normal blood sedimentation rate?
Reference ranges vary by age and sex. As a general guide, commonly cited upper limits in UK laboratories are around 15–20 mm/hr for men and 20–30 mm/hr for women, though these thresholds may differ depending on age and the laboratory used. Always refer to the reference interval provided on your specific blood report.
What does a high ESR result mean?
A high ESR may indicate that inflammation is present, but it does not identify the cause. It can be associated with infections, autoimmune conditions, anaemia, pregnancy and other factors. A healthcare professional should interpret a high result in the context of your symptoms and other investigations.
What does a low ESR result mean?
A low ESR is generally of limited clinical significance, but in some circumstances it may be associated with conditions such as polycythaemia or certain haematological disorders. If you are concerned about a low result, discuss it with a healthcare professional.
Can ESR detect inflammation?
ESR can indicate that inflammation may be present, but it cannot confirm it, identify its location or determine the cause. It is best described as a non-specific marker that should be interpreted alongside other clinical information.
Is the ESR test the same as a CRP test?
No. Both tests can reflect inflammation, but they respond differently. CRP rises and falls rapidly with acute inflammation, while ESR changes more slowly. They provide complementary rather than identical information and are not interchangeable.
What can affect ESR results?
Age, sex, pregnancy, anaemia, obesity, certain medicines, polycythaemia and some blood disorders can all influence ESR. Technical factors, such as time between sample collection and analysis, may also affect results.
How is an ESR test performed?
A blood sample is taken from a vein, typically in the arm. In the laboratory, the blood is placed in a calibrated tube and left vertical for one hour. The distance red blood cells settle during that time, measured in millimetres per hour, is the ESR result.
How can a high ESR be managed?
ESR is a marker, not a condition in itself. A high result is managed by identifying and appropriately treating the underlying cause. Addressing the cause — under the guidance of a healthcare professional — may result in ESR returning towards the reference range over time.
Should I be worried if my ESR is slightly elevated?
A mildly elevated ESR without accompanying symptoms is not always cause for concern. However, any unexplained or persistent elevation should be discussed with a healthcare professional who can assess the result in the context of your overall health.
Can I have an ESR test done privately in London?
Yes. Private blood testing in London can provide access to ESR tests and a range of other blood markers. You can view available options and book an appointment or check blood test prices at Private Blood Tests London. Private testing should complement, not replace, assessment by a qualified healthcare professional.
This article is intended for informational purposes only. It does not constitute medical advice, a diagnosis or a recommendation for treatment. If you have concerns about your health or any blood test result, please consult a qualified healthcare professional.