Principle of ESR:

When an anticoagulant is added to the blood and this well mixed venous blood is placed in a vertical tube, erythrocytes tend to settle towards bottom leaving clear plasma on top. This rate of sedimentation of red blood cells in a given interval of time is called erythrocyte sedimentation rate (ESR).

As the erythrocytes sediments, in a period of one hours, 3 stages can be observed.

• Stage I: first 10 minutes
  • It is initial period of aggregation during which rouleaux are formed and the sediment rate is low
• Stage II: next 4o minutes
  • It is a period of fast setting. Sedimentation occurs at a constant rate during this period

• Stage III: next 10 minute or more
  • The sedimentation again slows as it is the final period of packing of cells at the bottom of the tube

Factors affecting ESR:

• There are several factors that affects sedimentation of erythrocytes.

• Factors that increases ESR:

  • Anemia:
    • anemia increase ESR because the change in erythrocyte-plasma ratio favors rouleaux formation.
    • Rouleaux is aggregation of RBCs together due to their discoid shape.
    • Rouleaux have a decrease surface area and accelerate ESR
  • Increase level of fibrinogen:
    • it decreases the negative charge of erythrocyte, so RBC tend to remain apart and this promotes formation of rouleaux and increase ESR
  • Immunoglobulin:
    • increase antibody level in blood increase ESR
  • Increase cholesterol level
  • Rheumatoid arthritis
  • Chronic infections
  • Carcinoma
  • Tissue destruction and other disease

• Factors that decrease ESR:

  • Defibrinigenation:
    • removal of fibrinogen decreases ESR
  • Increase albumin and lecithin in blood
  • Abnormal or sickle shape RBCs:
  • abnormal or irregular shape of RBC lower ESR
  • Congestive heart failure

Method for ESR estimation:

Westergren method for ESR estimation is widely used method. Wintrobe method is also used for ESR determination. Wintrobe tube is smaller than westergren tube

Materials required:

1. Westergren tube or wintrobe tube
2. Anticoagulant: 0.1 M sodium citrate
3. ** in modified westergren method EDTA is used as anticoagulant

Procedure for ESR estimation:

• Withdraw 4 ml of venous blood
• Mix exact 10ml of sodium citrate with 4ml of venous blood in a tube
• Invert the tube 2-3 times to mix the blood thoroughly with anticoagulant
• Fill the westergren tube up to mark 0 and place in the rack at room temperature undisturbed and away from sunlight.
• Take the reading exactly after 1 hour. Record in millimeters from top surface of column to top of RBC sediments.

Result:

• Normal value of ESR
  • Female:
    • under 50 years- 20 mm/hr
    • above 50 years- 30mm/hr
  • Male:
    • Under 50 years- 15mm/hr
    • Above 50 years- 20 mm/hr

Clinical application of ESR estimation:

• ESR test is non-specific test although it is used as indication of presence of disease
• ESR value increase during rheumatoid arthritis, chronic infection, carcinoma, tissue destruction and nephritis
• During pregnancy, ESR increase moderately from 10^th or 12^th weeks onwards and return to normal after delivery.
• ESR value decreases in sickle cell anemia and congestive heart failure (CHF).

Erythrocyte sedimentation rate (ESR): principle, method, procedure and clinical application

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