Determination of erythrocyte sedimentation rate (ESR)
There are two main methods used to measure the ESR:
- Westergren method
- Wintrobe Method
Each method produces slightly different results. Most laboratories use the Westergren method.
Westergren method
- The Westergren method requires collecting 2 ml of venous blood into a tube containing 0 .5 ml of sodium
citrate. It should be stored no longer than 2 hours at room temperature or 6 hours at 4 °C. - The blood is drawn into a Westergren-Katz tube to the 200 mm mark. The tube is placed in a rack in a strictly vertical position for 1 hour at room temperature, at which time the distance from the lowest point of the surface meniscus to the upper limit of the red cell sediment is measured.
- The distance of fall of erythrocytes, expressed as millimeters in 1 hour, is the ESR.
Wintrobe method
- The Wintrobe method is performed similarly except that the Wintrobe tube is smaller in diameter than the Westergren tube and only 100 mm long.
- EDTA anticoagulated blood without extra diluent is drawn into the tube, and the rate of fall of red blood cells is measured in millimeters after 1 hour.
- The shorter column makes this method less sensitive than the Westergren method because the maximal possible abnormal value is lower.
However, this method is more practical for demonstration purposes.
Values
Average values in healthy men are: <15mm/hr; in healthy females, they are somewhat higher: <20mm. The values are slightly higher in old age, in both genders.
Theoretical considerations
The RBCs sediment because their density is greater than that of plasma; this is particularly so, when there is an alteration in the distribution of charges on the surface of the RBC (which normally keeps them separate form each other) resulting in their coming together to form large aggregates known as rouleaux.
Rouleaux formation is determined largely by increased levels of plasma fibrinogen and globulins, and so the ESR reflects mainly changes in the plasma proteins that accompany acute and chronic infections, some tumors and degenerative diseases. In such situations, the ESR values are much greater than 20mm/hr.
Note that the ESR denotes merely the presence of tissue damage or disease, but not its severity; it may be used to follow the progress of the diseased state, or monitor the effectiveness of treatment
Some interferences which increase ESR
- increased level of fibrinogen, gamma globulins.
- technical factors: tilted ESR tube, high room temperature.
Some interferences which decrease ESR
- abnormally-shaped RBC (sickle cells, spherocytosis).
- technical factors: short ESR tubes, low room temperature, delay in test performance (>2 hours), clotted blood sample, excess anticoagulant, and bubbles in the tube.
First Year B Pharm Notes, Syllabus, Books, PDF Subjectwise/Topicwise
Suggested readings