What is an ESR Test?
An Erythrocyte Sedimentation Rate (ESR) test is a simple blood test that measures how quickly your red blood cells (erythrocytes) settle or "sink" to the bottom of a tall, thin tube over one hour.
Think of it as a "clumping" test. It doesn't diagnose any single disease, but it's a very useful non-specific marker of inflammation in the body. The final result is measured in millimetres per hour (mm/hr).
How Does It Work? The "Stacking" Effect
The science is simple but clever. In normal, healthy blood, your red blood cells repel each other and sink slowly.
However, when inflammation is present (from an infection, injury, or autoimmune disease), your body produces extra proteins, especially fibrinogen. These proteins act like glue, causing your red blood cells to stick together in stacks, like coins. These stacks are called "rouleaux".
These heavy stacks of cells sink much faster than single cells. A faster sinking = a higher ESR, which tells your doctor that inflammation is likely present.
When Is an ESR Test Ordered?
- To detect or confirm inflammation when you have non-specific symptoms like fever, fatigue, weight loss, or joint pain.
- To help support a diagnosis for conditions like rheumatoid arthritis, lupus, or temporal arteritis.
- To monitor disease activity and see how well treatment is working for a known chronic inflammatory disease.
The Test Process: What to Expect
The ESR test is a simple blood draw, usually from a vein in your arm. In the lab, the Westergren method is the standard. Your blood is placed in a tall, 200mm tube and left undisturbed for exactly one hour. After 60 minutes, the technician measures the (mm) of clear plasma at the top, giving you the final "mm/hr" result.
Understanding Your Results: Normal Values
Normal ESR values are strongly dependent on age and sex. As we get older, our "normal" ESR levels tend to increase. Always compare your result to the reference range provided by your lab.
| Patient Group | Representative Normal Range (mm/hr) |
|---|---|
| Men < 50 years | < 15 mm/hr |
| Men ≥ 50 years | < 20 mm/hr |
| Women < 50 years | < 20 mm/hr |
| Women ≥ 50 years | < 30 mm/hr |
| Children | 3 – 13 mm/hr |
What Does a High ESR Mean?
An elevated ESR confirms the presence of inflammation, but it doesn't tell you the cause. Your doctor will use this as a clue, along with your symptoms and other tests (like a TLC or CRP).
Common Causes of a High ESR
- Autoimmune & Inflammatory Disorders: This is a key use. Conditions like rheumatoid arthritis, lupus, polymyalgia rheumatica, and temporal arteritis often cause very high ESR.
- Infections: Both acute and chronic infections, especially tuberculosis, osteomyelitis (bone infection), and endocarditis (heart valve infection).
- Cancers: Some cancers, particularly lymphoma and multiple myeloma, produce abnormal proteins that cause a very high ESR.
- Other Conditions: Chronic kidney disease, thyroid disorders, and anemia (a low red blood cell count) can also raise the ESR.
Red Flag: A very high ESR (e.g., > 100 mm/hr) strongly suggests a significant underlying disease (like a severe infection, malignancy, or major systemic inflammation) and almost always requires further investigation.
What Does a Low ESR Mean?
A low ESR is much less common and usually not a primary concern. It simply means your blood cells are sinking very slowly.
- Abnormal Red Blood Cells: Conditions like sickle cell anemia or spherocytosis change the shape of RBCs, making them unable to stack. No stacking means no fast sinking.
- Polycythemia: This is the opposite of anemia—a very *high* red blood cell count. The blood is "thicker," which makes it harder for the cells to settle.
Limitations: The "Slow" Test (ESR vs. CRP)
The ESR has two main limitations: it's non-specific (it can't pinpoint the problem) and it's slow.
Key Clinical Point: The ESR is often compared to C-Reactive Protein (CRP). Think of CRP as your "fast" inflammation marker. It rises and falls very quickly (within hours) in response to acute inflammation. The ESR is "slow" and "sluggish"—it can take days to rise and weeks to fall.
This makes CRP better for detecting acute, new infections, while the ESR is often better for monitoring chronic diseases (like rheumatoid arthritis) over the long term.