Erythrocyte Sedimentation Rate, Procedure and Interpretations

Erythrocyte sedimentation rate is a hematological test that measures the rate of fall of a column of red cells in plasma in 1 hour when placed in a vertical tube.

The principle applied in Erythrocyte sedimentation rate

The ESR is determined by filling a narrow tube of predetermined length and bore, with well-mixed anticoagulated blood, placing it in a vertical position for a set time.

Because of gravity and bearing in mind that erythrocyte is heavier than plasma they therefore fall, at the end of which the distance from the top of the column to the interface between the plasma and the sedimented red cells is recorded and expressed in mm/unit time.

Stages in Erythrocyte sedimentation rate

Erythrocyte sedimentation takes place in three stages.

1. An initial period of a few minutes (approximately 10 minutes) during which rouleaux formation takes place
2. A period of approximately 40 minutes during which settling or sedimentation occurs at a more or less constant rate. This is the most significant phase. 
3. A slower rate of fall (last 10 minutes) during which packing of the sedimented red cell column occurs.

Methods of Erythrocyte sedimentation rate

Two basic methods have been recommended and have gained wide acceptance. These are the Westergren and Wintrobe methods.

Westergren method

This is the ICSH (International Council for standardization in Hematology) reference method for ESR determination.

Advantages of the Westergren method

It more reliably reflects the clinical state and is the most sensitive method for the serial study of chronic diseases e.g. tuberculosis.

Disadvantages of the Westergren method

It requires a large amount of blood and involves dilution which may be one source of error.

Interpretation of results

Reference value Men: 0-15mm/hr.; Women: 0-20mm/hr.

There is a progressive increase with age because of the decline in plasma albumin concentration. The ESR increases in pregnancy as there is a decrease in plasma albumin due to hypervolemia and an increase in concentration of α-globulin and fibrinogen.

Wintrobe Method

It uses a tube closed at one end, 11cm long with a bore of 2.5mm and has a graduated scale from 0-100mm and a special Wintrobe rack.

Advantages of Wintrobe Method

The method is simple, requires a small amount of blood and there is no dilution.

With the same preparation, once the ESR has been read, the hematocrit value can be determined.

Microbilirubin determined can be made on Supernatant plasma and smears of a buffy coat can be made.

Disadvantages of Wintrobe Method

Because of the short column, it is only sensitive when the ESR is low and when the disease is in the acute stage.

Factors affecting erythrocyte sedimentation rate

I. Effect of plasma proteins

Red cells possess a net negative charge (zeta potential) and when suspended in normal plasma, rouleaux formation is minimal and sedimentation is slow.

Alterations in proportions and concentrations of various hydrophilic protein fractions of the plasma following tissue injury or in response to inflammation reduce the zeta potential and increase the rate of rouleaux formation and the size of the aggregates thus increasing the rate of sedimentation.

II. Influence of plasma viscosity

The ESR and plasma viscosity in general increase in parallel. However, plasma viscosity may increase to the extent of masking the rouleaux forming property of the plasma proteins.

III. Effect of red cell factors

Anisocytosis and poikilocytosis will reduce the ability of the red cells to form large aggregates thus reducing the sedimentation rate. Anemia by altering the ratio of red cells to plasma encourages rouleaux formation and accelerates sedimentation.

IV. Effect of mechanical influences

The conditions under which the Erythrocyte sedimentation rate is performed may influence the results. Perpendicularity of the sedimentation tube-slight deviations from the vertical will increase the rate of sedimentation.

v. Effect of temperature

Higher temperatures cause falsely elevated results due to a reduction in plasma viscosity.

Clinical significance of erythrocyte sedimentation rate

Increased levels of ESR has been implicated in:

i. Infectious diseases
ii. Neoplastic, invasive tumors.
iii. Anaemias.
iv. Chronic and acute diseases of liver.
v. Diseases of connective tissues.
vi. Inflammatory diseases e.g. rheumatoid arthritis

Physiologically ESR levels can also be increased in the following factors:

a) Increases with age.
b) During pregnancy.
c) After meals.
d) After hot baths.
e) During menstruation.
f) After physical exercises.