Erythrocyte sedimentation rate (ESR) is the rate at which the erythrocytes settle down. ESR is a simple and inexpensive laboratory test. It is commonly used often as a nonspecific measure in monitoring disease activity and assisting in the diagnosis of many inflammatory disorders caused by one or more conditions such as infections, tumors or autoimmune diseases to help diagnose and monitor specific conditions such as rheumatoid arthritis, systemic vasculitis, inflammatory bowel disease, temporal arteritis and many more.

Inflammation may also be a sign of a chronic disease, an immune disorder, or other medical condition. Normally, red blood cells settle relatively slowly. A faster-than-normal rate may indicate inflammation in the body.

ESR is the measurement of the suspension stability of red bloodcells (RBCs) in plasma under specified test conditions. The descent of the plasma-red cell interface is plotted against time, forming a typical sigmoid curve with three distinct phases. 

The initial portion of the curve, the lag phase, the red cells form a characteristics rouleaux pattern and sedimentation is generally slow. 

During the second, decantation phase, the plasma-red cell interface falls more rapidly. 

During the final phase, the cell aggregates pile up on the bottom of the tube. The two main determinants of ESR are degree of red cell aggregation and packed cell volume (hematocrit). The ESR test result, read at 60 minutes will include varying contributions from the three phases.

Phases of ESR

  1. Phase of rouleaux formation – 10 minutes
  2. Phase of sinking – 40 minutes
  3. Phase of packing – 10 minutes

Principle of ESR

When anticoagulated blood is placed in a vertical tube and allowed to stand, RBCs settle towards the bottom of the tube leaving clear plasma above.

The cells settle down due to:-

  • Density of RBCs is greater than that of plasma.
  • RBCs tend to aggregate to form rouleaux.

Clinical significance of ESR

ESR increases in disease such as the following conditions:

  • Anemia
  • Tuberculosis
  • Inflammatory disease
  • Pregnancy
  • Rheumatoid arthritis
  • Macrocytosis
  • Multiple myeloma
  • Acute and chronic infection

ESR decreases in following conditions:

  • Polycythemia
  • Sickle cell anemia
  • Decreased fibrinogen levels
  • Allergic conditions
  • Peptone shock
  • Hyperviscosity
  • Microcytosis
  • Spherocytosis

Determination of ESR

There are mainly two methods to determine ESR:-

  •    Westergren method
  •    Wintrobe method

Westergren method:

In this method, Westergren tube is used to determine ESR.

Westergren tube:

  • It is a straight glass tube, opened on both ends.
  • The tube is 300 mm long and 2.5 mm in diameter with a capacity of 1 ml.
  • It is marked 0 to 200 mm from above downwards.
  • Specially made racks with adjustable leveling screws are available for holding the tybe in vertical position.

Apparatus required:

  • Westergren tube
  • Westergren tube stand
  • Rubber bulb       
  • Timer or watch
  • 3.8% sodium citrate
  • Whole blood sample in EDTA (anticoagulant)

NOTE:- The procedure must be performed within 2 hours of blood collection.

Procedure:

  • Mix 1.6 mL of blood with 0.4 mL of 3.8% sodium citrate (anticoagulant) and loaded in the Westergren tube up to mark ‘0’ with the help of rubber bulb.
  • The ratio of blood and anticoagulant is 4:1.
  • The tube is fitted to the stand vertically and left undisturbed.
  • The reading is taken at the end of 1 hour.
  • Note the level to which the red cells column has fallen.
  • Report the result in terms of mm in 1 hour.

Normal values:

In males              :     3 to 7 mm in 1 hour

In females          :     5 to 9 mm in 1 hour

Infants                :     0 to 2 mm in 1 hour

Wintrobe method:

In this method, Wintrobe tube is used to determine ESR.

Wintrobe tube:

  • Wintrobe tube is a short tube opened on only one end.
  • It is 110 mm long with 3 mm bore. Wintrobe tube is used for determining ESR and PCV.
  • It is marked on both sides. On one side the marking is from 0 to 100 (for ESR) and on other side from 100 to 0 (for PCV).

Apparatus required:

  • Wintrobe tube
  • Wintrobe tube stand
  • Pasteur pipette  
  • Timer or watch
  • Whole blood sample in EDTA (anticoagulant)

NOTE:- The procedure must be performed within 2 hours of blood collection.

Procedure:

  • About 1 mL of blood is mixed with anticoagulant, ethylenediaminetetraacetic acid (EDTA).
  • Fill the blood in the tube up to ‘0’ mark using Pasteur pipette.
  • Place the tube in exact vertical position on the Wintrobe stand.
  • The reading is taken at the end of 1 hour.
  • Note the level to which the red cells column has fallen.
  • Report the result in terms of mm in 1 hour.

Normal values:

In males                :   0 to 9 mm in 1 hour

In females             :   0 to 15 mm in 1 hour

Infants                   :   0 to 5 mm in 1 hour

Variations of ESR

  • Age:-  ESR is less in children and infants because of more number of RBCs.  Whereas, in old age, ESR is high.
  • Sex:-  It is more in females than in males because of less number of RBCs.
  • Menstruation:- The ESR increases during menstruation because of loss of blood and RBCs.
  • Pregnancy:-  From 3rd month to parturition, ESR increases up to 35 mm in 1 hour because of hemodilution and returns to normal about four weeks after delivery.

Factors affecting ESR

Factors increasing ESR:

  • Specific gravity of RBC:- When specific gravity of RBC increases, the cells become heavier and sedimentation is fast. So, ESR increases.
  • Increase in size of RBC:- When size of RBC increases (macrocyte), ESR also increase.
  • RBC count:- When RBC count decreases, ESR increases.
  • Rouleaux formation:- When rouleaux formation increases, rate of sedimentation of RBC also increases.
  • Plasma factors:- High concentration of fibrinogen and immunoglobulin will lead to increase rouleaux formation and increases ESR.
  • White blood cells:- Extreme elevation of WBC count (leukemia) increases ESR.

Factors decreasing ESR:

  • Shape of RBC:- Change in shape of RBC (like sickle cell anemia, poikilocytosis) decreases ESR.
  • Viscosity of blood:- Viscosity offers more resistance for settling of RBCs. So when the viscosity of blood increases, the ESR decreases.
  • RBC count:- When RBC count increases, the viscosity of blood is increased and ESR decreases.
  • Albumin concentration:- When albumin concentration increases, ESR decreases.

Technical error affecting the ESR

  • If specimen is too old (EDTA > 4 hours) results in crenation and sphering, decreasing the ESR.
  • Presence of bubble in the tube will cause a falsely increase ESR.
  • Inaccurate timing (less than or greater than 1 hour).
  • An increase in temperature increases the ESR, a decrease in temperature decreases the ESR.
  • If ESR tube is not in vertical position, it results in an increased ESR.
  • Direct sunlight on ESR tube increases ESR.
  • Vibration of ESR tubes results in an increased ESR.
  • If blood is mixed with wrong anticoagulant the result will be not correct. (EDTA or tri-sodium citrate should be used).