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Hematology

ESR

Overview of Erythrocyte Sedimentation Rate (ESR)

  • Definition: The erythrocyte sedimentation rate (ESR) is a non-specific blood test that measures the rate at which red blood cells (RBCs) settle in a vertical tube over a period of one hour
  • Alternative Name: Sedimentation Rate, Sed Rate
  • Principle:
    • Erythrocytes settle more rapidly in the presence of increased levels of acute-phase proteins in the plasma (e.g., fibrinogen, globulins)
    • These proteins neutralize the negative charge on the RBC surface, reducing repulsion and promoting rouleaux formation (stacking of RBCs), which increases the sedimentation rate.
  • Clinical Significance:
    • Screening Test: A general indicator of inflammation and infection in the body, but it is not diagnostic for any specific condition
    • Monitoring Disease Activity: Used to monitor the course of inflammatory diseases (e.g., rheumatoid arthritis, polymyalgia rheumatica) and response to treatment
    • Detecting Occult Disease: Can be helpful in detecting hidden or occult inflammatory conditions
  • Limitations:
    • Non-Specific: The ESR is affected by many factors and can be elevated in a wide range of conditions
    • Lacks Sensitivity: The ESR may be normal in some patients with active inflammation
    • Affected by Physiological Factors: Age, sex, pregnancy, and certain medications can affect the ESR
    • Cannot localize the affected region

Methods for Measuring ESR

  • Westergren Method:

    • The most commonly used method
    • Uses a Westergren tube (a long, glass or plastic tube with a calibrated scale)
    • Procedure:
      1. Collect blood in an EDTA (purple-top) tube
      2. Mix the blood thoroughly
      3. Dilute the blood with sodium citrate or saline (4:1 ratio of blood to diluent)
      4. Fill the Westergren tube to the 0 mm mark
      5. Place the tube in a vertical rack and allow it to stand undisturbed at room temperature for 1 hour
      6. Read the distance (in millimeters) that the RBCs have fallen from the top of the column to the top of the packed red cells after 1 hour
      7. Report the result in mm/hr

  • Wintrobe Method:

    • Less commonly used
    • Uses a Wintrobe tube (a shorter, thicker glass tube with a calibrated scale)
    • Procedure:
      1. Collect blood in an EDTA (purple-top) tube
      2. Mix the blood thoroughly
      3. Fill the Wintrobe tube to the 0 mm mark
      4. Place the tube in a vertical rack and allow it to stand undisturbed at room temperature for 1 hour
      5. Read the distance (in millimeters) that the RBCs have fallen from the top of the column to the top of the packed red cells after 1 hour
      6. Report the result in mm/hr

  • Automated ESR Analyzers:

    • Some automated hematology analyzers can perform ESR measurements
    • These methods are based on different principles than the manual methods, such as:
      • Capillary photometry: Measures the rate of RBC aggregation in a capillary tube using optical sensors
      • Microfluidic technology: Measures the sedimentation rate in a microfluidic channel

Factors Affecting the ESR

The ESR can be affected by several factors, both physiological and pathological. It’s important to consider these factors when interpreting ESR results.

  • Factors that Increase ESR:

    • Increased Acute Phase Reactants: Fibrinogen, α-globulins, and other acute-phase proteins increase RBC aggregation
    • Rouleaux Formation: Increased rouleaux formation accelerates RBC sedimentation
    • Anemia: Decreased RBC concentration reduces the competition for sedimentation
    • Macrocytosis: Larger RBCs settle faster
    • Female Sex: Females tend to have higher ESR values than males due to hormonal influences
    • Age: ESR tends to increase with age
    • Pregnancy: ESR is elevated during pregnancy
    • Technical Factors: Tilting of the ESR tube, improper temperature

  • Factors that Decrease ESR:

    • Abnormal Red Blood Cell Shape: Sickle cells or spherocytes hinder rouleaux formation and sedimentation
    • Polycythemia: Increased RBC concentration slows down sedimentation
    • Hypofibrinogenemia: Decreased fibrinogen levels reduce rouleaux formation
    • Very High Leukocytosis: Increased cell numbers can affect the test
    • Technical Factors: Clotted sample, air bubbles in the tube

Clinical Significance of ESR

  • Elevated ESR:
    • Inflammatory Conditions:
      • Rheumatoid arthritis
      • Systemic lupus erythematosus (SLE)
      • Polymyalgia rheumatica
      • Giant cell arteritis
    • Infections:
      • Bacterial infections (e.g., pneumonia, osteomyelitis)
      • Tuberculosis
      • Fungal infections
    • Malignancies:
      • Multiple myeloma
      • Lymphoma
      • Metastatic cancer
    • Tissue Damage:
      • Trauma
      • Surgery
    • Other Conditions:
      • Pregnancy
      • Chronic kidney disease
      • Thyroid disorders
  • Normal or Decreased ESR:
    • Does not rule out significant disease
    • May be seen in:
      • Early stages of inflammatory conditions
      • Non-inflammatory conditions
      • Technical errors

Quality Control

  • Use Proper Technique:
    • Follow standardized procedures for sample collection, dilution, and reading
    • Avoid introducing air bubbles into the tube
    • Ensure that the tube is placed in a vertical rack
  • Check Reagents and Equipment:
    • Use fresh reagents and ensure that they are stored properly
    • Verify the accuracy of the pipettes and measuring devices
    • Maintain the centrifuge and other equipment according to the manufacturer’s instructions
  • Run Controls:
    • Use control materials with known ESR values
    • Monitor control results to ensure accuracy and precision
  • External Quality Assurance:
    • Participate in proficiency testing programs to assess the performance of the laboratory’s ESR testing

Reporting Results

  • Report the ESR value in the appropriate units (mm/hr)
  • Include the reference range for the patient’s age and sex
  • Note the method used (e.g., Westergren, Wintrobe)
  • Qualify the results with any relevant comments (e.g., “Elevated ESR, clinical correlation advised”)
  • Always interpret results in conjunction with clinical information!

Key Terms

  • Erythrocyte Sedimentation Rate (ESR): A test that measures the rate at which red blood cells settle in a tube
  • Westergren Method: A common method for measuring ESR
  • Wintrobe Method: Another method for measuring ESR
  • Rouleaux Formation: Stacking of red blood cells
  • Acute-Phase Proteins: Proteins whose serum concentrations increase or decrease in response to inflammation
  • Inflammation: A complex biological response to harmful stimuli
  • ESR is not specific: a lot of things can cause it to elevate
  • ESR to monitor therapy: if a disease is already known, ESR can be used to see if treatments are working to alleviate the elevated ESR