The erythrocyte sedimentation rate (ESR) is a blood test that measures how quickly red blood cells (erythrocytes) settle at the bottom of a test tube containing a blood sample. Normally, red blood cells settle relatively slowly. A faster-than-normal rate may indicate inflammation in the body.
Principle of ESR
The ESR is based on the principle of gravity and the aggregation tendency of erythrocytes. In normal blood, erythrocytes have a negative charge, which causes them to repel each other and settle slowly. However, the acute phase increases in the bloodstream when inflammatory processes occur. These proteins cause erythrocytes to lose their negative charge and form rouleaux stacks, which settle faster due to increased density. The ESR reflects the extent of inflammation, where a faster settling rate correlates with more inflammation.
Methods of ESR Determination
Westergren Method (Gold Standard)
Materials Required
- Anticoagulant: The most commonly used is sodium citrate (3.8%). Alternatively, EDTA-treated blood can be converted for use in the Westergren method.
- Westergren tube:
- Length: 200 mm
- Internal diameter: 2.55 mm
- Calibrated from 0 to 200 mm
- Length: 200 mm
- Rack/Stand: A vertical stand to hold the Westergren tubes upright.
- Venous blood sample:
- Blood mixed with sodium citrate in a ratio of 4:1 (4 parts blood to 1 part anticoagulant).
- Pipette: To transfer blood to the Westergren tube.
- Timer: To accurately time 1 hour.
Procedure
- Blood Collection:
- Collect 2 mL of venous blood from the patient and mix it with 0.5 mL of sodium citrate (3.8%) in a collection tube. The blood should be mixed gently to prevent clotting without causing hemolysis.
- Filling the Westergren Tube:
- Place the anticoagulated blood in the Westergren tube, using a pipette, up to the zero mark (0 mm).
- Ensure no air bubbles are present in the tube, as air bubbles can interfere with the accuracy of the reading.
- Placing the Tube in the Stand:
- Place the tube vertically in the rack or stand. Ensure the tube is upright and undisturbed. Any tilting or movement can alter the sedimentation rate.
- Sedimentation Time:
- Allow the blood to sediment for exactly 1 hour at room temperature (18-25°C). External factors like vibrations, temperature changes, or light exposure should be avoided during this time, as they may affect the result.
- Reading the ESR:
- After 1 hour, measure the distance in millimeters from the zero mark to the top of the red blood cell column. This distance represents the ESR in mm/hour.
- If sedimentation is unusually high or low, recheck the process for any errors or interference.
Normal ESR Values
- Men:
- Under 50 years: 0-15 mm/hour
- Over 50 years: 0-20 mm/hour
- Women:
- Under 50 years: 0-20 mm/hour
- Over 50 years: 0-30 mm/hour
- Children: 0-10 mm/hour
- Newborns: 0-2 mm/hour
- Pregnant women May show values up to 20-50 mm/hour, especially during the second and third trimesters due to physiological changes.
Wintrobe Method
Materials Required
- Wintrobe tube:
- Length: 100 mm
- Diameter: 3 mm (narrower than the Westergren tube)
- Markings: Graduated in 1 mm divisions, with a scale from 0 to 100 mm on one side for ESR and another for hematocrit measurement.
- Length: 100 mm
- Anticoagulant:
- EDTA (ethylene diamine tetra-acetic acid) or sodium citrate can prevent blood clotting.
- Venous blood sample:
- About 1 mL of blood is needed.
- Rack/Stand:
- A vertical stand is necessary to hold the Wintrobe tube during the test.
- Pipette:
- Used to transfer the blood into the Wintrobe tube.
- Timer:
- To measure the sedimentation period (1 hour).
Procedure
- Blood Collection:
- Draw approximately 1-2 mL of venous blood from the patient into an anticoagulant (EDTA or sodium citrate) tube. Mix gently to avoid hemolysis or clotting.
- Filling the Wintrobe Tube:
- Transfer the anticoagulated blood to the Wintrobe tube using a pipette to the ESR scale’s zero mark. Ensure no air bubbles are present, as this can affect the accuracy of the result.
- Positioning the Tube:
- Place the Wintrobe tube vertically in a stand. Ensure the tube is perfectly upright because any tilt can affect the erythrocyte sedimentation rate.
- Sedimentation Time:
- Leave the tube undisturbed at room temperature (18-25°C) for exactly 1 hour. External vibrations or temperature fluctuations should be avoided, as they can impact the sedimentation rate.
- Reading the ESR:
- After 1 hour, measure the distance in millimeters that the red blood cells have fallen from the zero mark to the top of the column of red blood cells.
- This distance represents the ESR in mm/hour.
- Recording the Results:
- Report the result as the ESR in mm/hour. A higher sedimentation rate indicates a greater degree of inflammation.
Normal Values
- Men: 0-9 mm/hour
- Women: 0-20 mm/hour
- Children: 0-10 mm/hour
Advantages of the Wintrobe Method
- Less blood required: This method is often used when a smaller blood sample is available (such as in pediatric patients).
- Simultaneous hematocrit measurement: Using the same blood sample, the Wintrobe tube can also measure hematocrit (the proportion of blood that consists of red blood cells).
Disadvantages of the Wintrobe Method
- Less sensitive to high ESR values: The shorter tube means this method is not as effective at measuring very high ESR levels (>100 mm/hour), making it less sensitive for detecting significant inflammatory processes.
- Standardization: The Westergren method is more commonly used and is better standardized, which is why many clinicians prefer it.
Automated ESR Machines
- Principle: These machines analyse the initial stages of erythrocyte aggregation and predict ESR values. They offer faster results compared to manual methods.
- Advantages: Automated, faster, reduces human error, and minimizes the influence of external variables.
- Disadvantages: More expensive and may not always be available in all settings.
Clinical Significance
The ESR test is a nonspecific marker, meaning it cannot diagnose specific diseases, but it is a valuable indicator of the presence and extent of inflammation in the body. ESR values can be elevated or decreased in a wide range of conditions:
Elevated ESR (conditions causing faster red cell sedimentation)
- Infections: Bacterial infections (e.g., pneumonia, tuberculosis), abscesses, and chronic infections.
- Inflammatory diseases:
- Autoimmune diseases (e.g., rheumatoid arthritis, systemic lupus erythematosus)
- Vasculitis (e.g., temporal arteritis)
- Inflammatory bowel diseases (e.g., Crohn’s disease, ulcerative colitis)
- Cancers:
- Malignancies (e.g., lymphoma, multiple myeloma, metastatic cancers)
- Chronic diseases:
- Chronic kidney disease
- Endocarditis
- Polymyalgia rheumatica
- Pregnancy: Due to increased fibrinogen levels.
Decreased ESR (conditions causing slower red cell sedimentation)
- Polycythemia: Increased number of red blood cells can cause a low ESR.
- Sickle cell anaemia: The abnormal shape of red blood cells prevents rouleaux formation, resulting in decreased ESR.
- Heart failure: Chronic heart conditions can sometimes result in a decreased ESR.
- Hyperviscosity syndromes: Conditions that increase blood thickness, such as Waldenstrom’s macroglobulinemia.
Factors Influencing ESR (Erythrocyte Sedimentation Rate)
A wide range of factors, both physiological and pathological, influences ESR. Understanding these factors is essential for accurate interpretation of ESR results:
-
Physiological Factors
- Age: ESR tends to increase with age, especially in the elderly, due to physiological changes, even without disease.
- Gender: Women typically have higher ESR values than men due to hormonal differences, especially during menstruation and pregnancy.
- Pregnancy: ESR increases significantly in pregnancy, particularly during the second and third trimesters. This is due to increased fibrinogen levels and other physiological changes.
- Menstruation: Due to hormonal variations, ESR may rise slightly during the menstrual cycle.
- Haemoglobin concentration: Anemia can elevate ESR as there are fewer red blood cells, making it easier for them to form rouleaux and sediment faster.
-
Pathological Factors
- Inflammation: Acute-phase proteins (e.g., fibrinogen, C-reactive protein, immunoglobulins) produced during inflammation promote rouleaux formation, increasing ESR.
- Infections: Bacterial and chronic infections significantly raise ESR due to the inflammatory response.
- Chronic diseases: Conditions like rheumatoid arthritis, systemic lupus erythematosus, and malignancies can increase ESR due to chronic inflammation.
- Cancer: Some cancers (e.g., lymphoma, multiple myeloma, metastatic tumours) cause elevated ESR due to the presence of cancer-related inflammation and tissue damage.
- Kidney disease: chronic kidney disease can cause elevated ESR due to the buildup of inflammatory proteins and other metabolic factors.
- Heart failure: Congestive heart failure can lower ESR, likely due to reduced fibrinogen levels and changes in blood viscosity.
- Polycythemia: Increased red blood cells in polycythemia can reduce ESR because the cells crowd the plasma and hinder rouleaux formation.
-
Technical and Environmental Factors
- Tilt of the ESR tube: A tube that is not perfectly vertical will cause the red blood cells to settle faster, artificially elevating the ESR.
- Temperature: ESR is temperature-sensitive. At higher temperatures, ESR may increase, while lower temperatures can slow sedimentation.
- Sample processing time: ESR measurements must be taken within 2 hours of blood collection. Delayed measurement can cause falsely elevated ESR due to blood changes over time.
- Tube size: The diameter and length of the ESR tube (Westergren vs. Wintrobe tubes) influence the sedimentation rate.
- Clotting: Inadequate anticoagulation or improper mixing can cause clumping of red blood cells, falsely lowering ESR.