Introduction
The Erythrocyte Sedimentation Rate (ESR) is a simple yet vital laboratory test that measures the rate at which red blood cells (RBCs) settle in a column of anticoagulated blood over a specific time, typically one hour.
It serves as a non-specific marker of inflammation and can assist in diagnosing various medical conditions.
Let’s dive deeper into the principle, procedure, and clinical significance of ESR.
Principle of ESR
When anticoagulated blood is allowed to stand in a vertical tube, red blood cells settle at the bottom due to gravity. The rate of this sedimentation depends on several factors, including:
- Plasma protein concentration: Elevated fibrinogen and globulin levels increase ESR by reducing the negative charge (zeta potential) of RBCs, causing them to aggregate.
- Red blood cell characteristics: Changes in size, shape, or number can influence the settling rate.
- Inflammation: During inflammation, acute-phase proteins like fibrinogen rise, enhancing RBC aggregation and increasing ESR.
The ESR is typically reported in millimeters per hour (mm/hr).
Methods of Estimating ESR
There are two commonly used methods for estimation:
- Westergren Method (Gold Standard)
- Procedure:
- Mix 4 parts of venous blood with 1 part of 3.8% sodium citrate as an anticoagulant.
- Fill a Westergren tube (200 mm long with a 2.5 mm bore) up to the 0 mark.
- Place the tube vertically in a stand at room temperature.
- Measure the distance (in mm) that RBCs have settled after 1 hour.
- Advantages: High sensitivity and reliability.
- Normal values:
- Men: 0–15 mm/hr
- Women: 0–20 mm/hr
- Children: 0–10 mm/hr
- Procedure:
- Wintrobe Method
- Procedure:
- Use a shorter Wintrobe tube (100 mm long) filled with anticoagulated blood.
- Place the tube vertically and measure sedimentation after 1 hour.
- Normal values:
- Men: 0–9 mm/hr
- Women: 0–20 mm/hr
- Limitations: Less sensitive compared to the Westergren method.
- Procedure:
Factors Affecting Erythrocyte Sedimentation Rate
Several factors can influence ESR values, including:
- Physiological: Age, gender, and pregnancy.
- Pathological: Infections, autoimmune disorders, malignancies, and anemia.
- Technical: Temperature, tube inclination, and improper anticoagulant-to-blood ratio.
Clinical Significance of ESR
Although ESR is a non-specific test, it is valuable for:
- Monitoring chronic conditions:
- Rheumatoid arthritis
- Tuberculosis
- Systemic lupus erythematosus (SLE)
- Diagnosing acute inflammatory diseases:
- Temporal arteritis
- Polymyalgia rheumatica
- Tracking disease progression and treatment response.
Limitations of ESR
While ESR is a useful test, it has its drawbacks:
- It is non-specific and does not pinpoint the exact cause of inflammation.
- Certain conditions, like polycythemia or sickle cell anemia, may falsely lower ESR.
For more precise assessments,it is often combined with other diagnostic tests, such as C-reactive protein (CRP) or complete blood counts (CBC).
Conclusion
The estimation of ESR remains a crucial test in medical laboratories, offering insights into inflammatory and pathological conditions. While it is a non-specific marker, its simplicity, cost-effectiveness, and utility make it an indispensable part of routine diagnostic work.
Understanding its principle, procedure, and clinical significance is vital for healthcare professionals and medical laboratory technologists.