Erythrocyte Sedimentation Rate
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The erythrocyte sedimentation rate (ESR) was first developed as a pregnancy test in the early 1900's. As such it was not a very reliable test but was then shown to have value as a non-specific marker of illness. Two methods have been used - Westergren or Wintrobe with the former method being the more commonly used method today.
Method
The test is performed by diluting whole blood in citrate at a dilution of 4:1. This whole blood may be anticoagulated with EDTA prior to dilution. The mixture is then aspirated into a vertical tube, which has a uniform internal diameter, to a height of 200mm. The distance that the red cells sediment down through the plasma in 1 hour is taken to be the ESR.
Sedimentation of red cells in this system is affected by forces both for and against sedimentation. The forces resisting sedimentation are the negative charge on the red cell surface (causing red cells to repel each other (zeta potential)), the upflow of plasma displaced by falling red cells, and the rigidity of red cells. The forces accelerating sedimentation are anaemia, and plasma proteins. Plasma proteins bind to red cell membranes thereby reducing the zeta potential thus allowing rouleaux formation to occur. There are a number of artifactual causes of an elevated ESR. These include vibration of the ESR tube, the tube being non-vertical, and the age of the sample (increasing age decreases the ESR).
The degree to which proteins reduce the zeta potential can be rated on a scale of 1-10: fibrinogen 10, beta-globulin 5, alpha globulin 2, gamma globulin 2, albumin 1.
Interpretation
The ESR is a non-specific test and so can be difficult to interpret. Recent trials of the ESR have demonstrated no value in screening asymptomatic individuals, because not only is the number of abnormals low but also in most cases the abnormal test returns to normal over several months without any significant diagnosis being made.
There is also little evidence of value in screening symptomatic patients because a complete history and physical examination is a much better tool for detecting abnormalities. Older text books suggest that an extensive search should be made for the cause of an elevated ESR but provide little evidence of the benefits of such a search. Recent cost-benefit analysis has suggested that tests in addition to a complete history and physical examination are not cost effective.
However, there are several groups of patients where the ESR is important, viz. patients suspected of having temporal arteritis or polymyalgia rheumatica. In these cases treatment is often initiated after an elevated ESR result is known and prior to a definitive biopsy. In these patients the diagnosis is difficult to sustain, but not excluded, if the ESR is normal.
The ESR can also be useful in monitoring certain groups of patients viz. rheumatoid arthritis, temporal arteritis, polymyalgia rheumatica, and Hodgkin's Disease (H.D.), where disease activity is mirrored by changes in the ESR.
There is debate as to whether this test is useful in distinguishing between organic and psychosomatic disease.
There is no evidence of any diagnostic value to the ESR when attempting to evaluate acutely ill patients already known to have acute or chronic infections, or cancer (except H.D.). Even in screening patients with possible myeloma the ESR has been replaced by measurement of total protein and globulin fraction.
References
- Sox H.C., Liang M.H. The Erythrocyte Sedimentation Rate. Ann. Int. Med. 1986: 104: 515-523.
- Fincher R-M., Page M.I. Clinical Significance of Extreme Elevation of the Erythrocyte Sedimentation Rate. Arch. Int. Med. 1986: 146: 1581-1583.
- Dacie J.V., Lewis S.M. Practical Haematology. Ed. Churchill Livingstone. 5th Ed 1977.
- Lee G.R., et al. Wintrobe's Clinical Haematology. Ed. Lea & Feriger. 9th Ed. 1993.
Written by: Dr Michael Seldon, Haematology HAPS
Written: November 1998
Last Reviewed: 10.5.2001