The Erythrocyte Sedimentation Rate (ESR) is one of the oldest and most widely used blood tests for detecting inflammation in the body. Despite the development of newer, more specific tests, ESR remains a valuable tool in clinical practice due to its simplicity and ability to provide insights into overall inflammatory status. This guide explains how the ESR test works, what it measures, and what your results may reveal about your health.
What is ESR?
ESR, also known as the erythrocyte sedimentation rate or "sed rate," measures how quickly red blood cells (erythrocytes) settle to the bottom of a test tube over one hour. Under normal circumstances, red blood cells settle relatively slowly. However, when inflammation is present in the body, certain proteins increase in the blood, causing red blood cells to clump together and fall more rapidly.
The test is beautifully simple in concept: a blood sample is placed in a tall, thin tube and left undisturbed for exactly one hour. The distance the red blood cells have fallen (in millimetres) is then measured. A higher ESR indicates more inflammation; a lower ESR suggests less inflammatory activity.
How Does Inflammation Affect ESR?
When your body experiences inflammation – whether from infection, autoimmune disease, injury, or other causes – it produces proteins called acute phase reactants. The most important of these for ESR is fibrinogen, a protein involved in blood clotting.
Elevated fibrinogen and other proteins cause red blood cells to stick together, forming stacks called rouleaux (resembling stacks of coins). These heavier clumps of cells sink faster through the plasma, resulting in a higher ESR reading.
Other factors affecting ESR include:
Why is an ESR Test Performed?
Healthcare providers may order an ESR test for several purposes:
Detecting Inflammation
ESR is a non-specific marker, meaning it indicates that inflammation exists somewhere in the body but does not pinpoint the location or cause. It is often used as a screening tool when inflammation is suspected.
Diagnosing Specific Conditions
ESR is particularly useful in diagnosing and monitoring certain inflammatory conditions:
Monitoring Disease Activity
For people with known inflammatory conditions, regular ESR testing helps track disease activity and assess how well treatment is working. A declining ESR often indicates that inflammation is being controlled.
Investigating Unexplained Symptoms
When patients present with vague symptoms like fatigue, fever, weight loss, or joint pain, ESR can help determine whether an inflammatory process is occurring.
ESR vs CRP: Understanding the Difference
Both ESR and C-Reactive Protein (CRP) are markers of inflammation, but they have different characteristics:
ESR:
CRP:
For more information about CRP testing, read our comprehensive guide on the C-Reactive Protein test.
Often, healthcare providers will order both tests together to get a complete picture of inflammatory activity.
The ESR Test Procedure
Having an ESR test is straightforward and requires minimal preparation:
Preparation
No special preparation is typically required for an ESR test. You can usually eat and drink normally beforehand. However, inform your healthcare provider about any medications you are taking, as some can affect results.
During the Test
A healthcare professional will draw a blood sample from a vein in your arm. The procedure takes just a few minutes and causes minimal discomfort. For detailed information about what to expect during a blood draw, see our guide on blood testing procedures, results, and after effects.
After the Test
You can resume normal activities immediately. The blood sample is processed in the laboratory, where it is placed in a special tube and monitored for one hour.
Understanding Your ESR Results
ESR is measured in millimetres per hour (mm/hr). Normal ranges vary based on age and sex:
Normal ESR Ranges:
A commonly used formula for estimating the upper limit of normal is:
ESR naturally increases with age, so what is considered normal for a 70-year-old would be elevated for a 25-year-old.
What Do Abnormal ESR Levels Mean?
Elevated ESR May Indicate:
Very High ESR (over 100 mm/hr) May Suggest:
Low ESR May Indicate:
Factors That Can Affect ESR Results
Several factors can influence your ESR independently of inflammation:
Limitations of the ESR Test
While ESR is valuable, it has important limitations:
For these reasons, ESR is best used alongside other tests and clinical assessment rather than in isolation.
When to Seek Medical Advice
At Private Blood Tests London, we provide your raw ESR test data. We recommend consulting your GP or healthcare provider if:
ESR as Part of Comprehensive Health Assessment
ESR is often included in broader health assessments alongside other inflammatory markers and general blood tests. At Private Blood Tests London, we offer comprehensive health screening packages that can include ESR testing as part of a complete health picture.
Book Your ESR Blood Test
Understanding your inflammatory status is an important aspect of monitoring your overall health. At Private Blood Tests London, we offer ESR testing at our CQC-registered clinic in South Kensington. Our experienced team ensures accurate sample collection, and your results are delivered quickly and securely.
Learn more about [the link between stress, cortisol and your blood results](/blog/the-link-between-stress-cortisol-and-your-blood-test-results) and explore our [health screening packages](/health-screening).
Take a proactive step in understanding your health – book your ESR blood test today.