Interpreting the ESR
"Few laboratory tests are performed more often than the erythrocyte sedimentation rate (ESR). Yet none can be more difficult to interpret. "
The ESR is one of the oldest tests in haematology, having first being developed by Fahraeus in 1918. It is an empirical, non specific, in vitro phenomenon which has been exhaustively investigated.. While it has many limitations, it continues to be a useful test in the eyes of many clinicians and newer tests have not yet managed to displace it in clinical medicine.
The numerical value of the ESR to the nearest millimetre is obtained by measuring the height of the clear plasma above the upper limit of the red cell layer. The test is subject to a number of technical errors and therefore the first step in the investigation of an unexpected result is to repeat the test. The rate of fall of red cells in anti-coagulated plasma is influenced by a number of factors. Briefly, sedimentation is influenced greatly by the extent to which the red cells form rouleaux or large clumps of cells. This rouleaux formation is related to the plasma proteins which overcome the negative surface charge on red cells. The haematocrit also influences the ESR. Anaemia accelerates sedimentation and polycythaemia retards it. Table 1 lists the factor which tend to influence the ESR.
The normal range for ESR is 0-10mm. With increasing age after 50 years, the ESR rises and, in the elderly, many apparently normal subjects have increased readings. Thus the ESR is of limited value in detecting disease in elderly patients. Physiological increases in the ESR occur in pregnancy and the puerperium.
The ESR is widely used in clinical medicine giving information of a general character with the same usefulness as body temperature, pulse rate and leucocyte count. It is a measure of the presence and severity of inflammatory and other morbid processes. While a normal ESR cannot be taken to exclude organic disease, the fact remains that most acute or chronic infections, neoplastic diseases, collagen diseases, renal or other diseases associated with changes in plasma proteins lead to acceleration of sedimentation. It is also useful in monitoring disease activity in certain disorders. It has been used for this purpose in tuberculosis, rheumatic fever, rheumatoid arthritis, Hodgkin's disease and non-Hodgkin's lymphomas, myeloma and macroglobulinaemia.
The investigation of a high ESR involves full clinical assessment of the patient which will usually reveal the cause. There are a number of well known associations with a high ESR which include the following:
From the laboratory point of view, investigations should include a repeat blood count and ESR, urinalysis, micro-urine, chest X-ray, biochemical profile including liver function tests, serum protein electropheresis and immunoglobulin quantitation, rheumatoid factor and anti-nuclear antibody. In the great majority of patients, these investigations will lead to the diagnosis. If not, further investigations including abdominal CT scanning or bone marrow biopsy may be appropriate.
In summary, despite its limitations, most clinicians agree that the ESR is still a useful test. It is used mainly as a screening test to confirm the presence of occult organic disease. A high ESR in this situation will confirm diagnosis with >90% certainty, but a normal ESR excludes nothing. It can also be used as a means of following the activity or clinical course of certain diseases that have already been recognised.
For Further information contact Dr Joanne Joseph (8382-2677).
|Last updated 13/03/2006|