When an anti-coagulated blood is allowed to stand vertically, sedimentation of erythrocyte occurs. The rate, at which erythrocytes fall down, is known as erythrocyte sedimentation rate (ESR).
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Principle:
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Anti-coagulated blood is taken in a tube and kept undisturbed in vertical position in a rack. This will allow the sedimentation of erythrocytes. After a specific time, generally 1 hr., the level of red cell is noted. The distance travelled by erythrocytes in 1 hr. is called as Erythrocyte Sedimentation Rate (ESR).
Methods:
There are two different methods of determination of ESR:
1. Westergren Method
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2. Wintrobe Method
Westergren Method:
Requirements:
1. Westergren Pipette
2. Westergren Stand
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3. Anticoagulant
Westergren pipette is open at both the ends. It is 30 cm in length and 2.5 mm in diameter. The lower 20 cm are marked with 0 at top and 200 at bottom.
The anticoagulant used in this method is 3.8% tri-sodium citrate solution. 0.4 ml of tri-sodium citrate is added in 2 ml of blood.
Procedure:
Fill the pipette by sucking blood upto 0 marks and fix it vertically in Westergren stand. Read the upper level of RBC column exactly after 1 hr.
1. Tube with anticoagulant
2. Addition of blood in the tube
3. Filling of Westergren pipette
4. Pipette on stand
5. The ESR level
Normal Values:
i. For males: 3 to 10 mm/hr
ii. For females: 5 to 15 mm/hr
Wintrobe Method:
Requirements:
1. Wintrobe Pipette
2. Anticoagulant
3. Wintrobe Stand
Wintrobe tube is open at one side only. The length of Wintrobe tube is 11 cm and the diameter is 2.5 mm. The lower 10 cm are marked. The marking is 0 at top and 100 at bottom for ESR, and it is also used for PCV (Packed Cell Volume).
The anticoagulant used in Wintrobe Method is EDTA solution. 0.4 ml of anticoagulant is required for 2 ml of blood.
Procedure:
With the help of long necked pasture pipette or a special syringe, fill the Wintrobe tube upto ‘0’ mark. Place the tube in an exactly vertical position in a Wintrobe stand. Read the upper level of RBC column exactly after 1 hr.
1. Addition of blood in anticoagulant
2. Taking blood in pasture pipette
3. Filling of pipette
4. Wintrobe tube in stand
5. The ESR level
Normal Values:
i. In males: 0 to 9 mm/hr
ii. In females: 0 to 20 mm/hr
Readings can be taken with a gap of every half hr. in both methods.
The Wintrobe Method is commonly practiced and more advantageous over Westergren Method. This is because of following reasons;
By Wintrobe Method, we can find out PCV in addition to ESR.
Icetric index, volume of packed leucocytes and platelets can be known.
Amount of blood required for Wintrobe Method is less than that of Westergren method.
Possible Errors in ESR:
The value of ESR can be affected by following errors.
a. Improper anticoagulant.
b. The tube is not exactly vertical in position. Slight inclination may result in great difference in ESR value. 3° angle of inclination may raise ESR upto 30%.
c. Dirty tube.
d. Bubble caused by too vigorous mixing of blood and anticoagulant.
e. Haemolysis may modify ESR.
f. Blood should be tested within 3 hours of collection. The prolonged storage may modify ESR.
g. The stand should not be kept on vibrating surface.
h. The reading should be taken exactly after 1 hour.
i. The stand should be kept away from window to avoid temperature variations.
Factors Affecting ESR:
There are three factors affecting ESR:
i. Plasma
ii. RBC
iii. Anticoagulant
Plasma:
Plasma proteins and other constituents of plasma affect the ESR level. Increased level of fibrinogen and globulin accelerate ESR. Albumin retards ESR. Extreme increase in plasma viscosity slows down ESR. Cholesterol accelerates ESR and lecithin retards ESR.
Red Cell:
Change in erythrocyte plasma ratio affects ESR. Anemia is responsible for accelerating ESR. Microcyte sediment slowly. The macrocyte sediment rapidly and normocyte sediment with normal speed. Poikelocytosis retards ESR. Besides these, high sugar, high phospholipids, administration of certain drugs, may affect ESR level.
Anticoagulant:
The use of anticoagulant with different proportion and improper anticoagulant may affect ESR value.
Importance and Limitations:
ESR is not diagnostic test for any particular disease. A raised ESR suggests progressive increase of disease. Therefore, normalization of ESR indicates the recovery from disease.
The rapid increased ESR is found in any chronic infection like, tuberculosis, lymphatic fever, toxemia, etc.
In pregnancy, after second month, ESR is increased. Myocardial infarction, anemia, syphilis, malignant tumor, menstruation, liver disease, etc. are related with rapid ESR.
The slow ESR is found in –
i. Newborn infants
ii. Polycythaemia
iii. Allergic conditions
iv. Heart failure, etc.
In this way, ESR is helpful to indicate the relative progress of the disease.