Technical information and Use Tips
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Principle of the ESR test
Anticoagulated blood is drawn up into a tube of standardised dimensions (these
days the Westergren dimensions are recommended 1) and left in a vertical
position for exactly one hour. After that period the point at which the red
cells have separated and settled from the plasma is recorded by reading from the
scale on the side of the tube.
Despite the fact that the test, in it's present form, has been in constant use
since 1926 the phenomenon of red cell sedimentation is still only partly
understood. However three definite phases have been identified in the process.
During the first, or Lag Phase, the red cells form a characteristic rouleaux
pattern and sedimentation is generally slow. The rate accelerates in the second
period, the Decantation Phase, and slows again in the final Packing Phase as red
cell aggregates pile up at the base of the tube.
The size of the rouleaux aggregates formed in the Lag Phase is the critical
factor affecting the final result of the ESR. The rouleaux itself appears to be
influenced mainly by certain plasma proteins including fibrinogen, IgM and
alpha2-macroglobulin. Opinions vary as to the accelerating and retarding
properties of glycoproteins & albumin.
From the above it can be seen that the sedimentation 'rate' of the red cells is
not linear. Further, the time taken for each of the three phases will differ
between patients. Therefore no attempt should be made to 'estimate' the result
at 1 hour by doubling the value at 30 minutes or multiplying by three after 20
minutes.
Factors Influencing the ESR
Although the test itself is subject to a number of variable factors affecting
the results, it is basically simple to perform and provided those variables are
carefully avoided the test is equally suited to the medical laboratory or the
doctors office. The factors that influence ESR results can be listed under two
headings. First, those physical changes in blood plasma and cells, which to some
degree the test is measuring and secondly those technical variables that must be
avoided when performing the test.
Physical Changes in Blood
The ESR is a manifestation of the interaction between red cells and plasma,
therefore any physical variation in either component of blood will affect the
result.
Plasma proteins that affect the ESR include the immunoglobulins (IgM) and a
number of the acute phase proteins including fibrinogen 2, C-reactive protein
3,
alpha-1-anti-trypsin, haptoglobin, etc. These acute phase proteins increase with
tissue damage (e.g. lupus or rheumatoid arthritis), pregnancy, chronic
inflammation and chronic infection.
Changes in the red cells that affect ESR include anaemia, which usually
increases the rate, and abnormal cell morphologies such as sickling (HbS), or
targeting, which slow the rate.
Technical Variables
It is vitally important that anyone setting up an ESR test is aware that a
number of external factors will affect the result.
Correct mixing of the blood sample at venepuncture and immediately before
setting up the test is one of the most important factors influencing the ESR
result. 1 Other factors of equal importance include the verticality of the
measuring tube (Dispette) 4, the ambient temperature at which the test is
performed 5, vibration and the dimensions of the measuring tube.
1
By using a commercial ESR test kit such as the Dispette 2 system, the effect of
most of these variables can be eliminated and the test performed with confidence
following the detailed instructions supplied with the kit.
Technical Tips for Performing the Test
Although Guest ESR systems are designed to make the test as accurate yet
as simple as possible to perform there are some general points that need
to be kept in mind when setting-up ESR tests.
1. The ESR measuring tube must be kept perfectly vertical. 4
The blue Guest ESR stand has a levelling bubble and levelling device
incorporated to assist, but the level should be checked regularly in
case of movement.
2. The ESR must be performed at room temperature (18 - 22°C or 65 –
72°F). 5 Keep the stand away from windows, direct sunlight or
draughts.
3. Vibration can seriously affect the ESR. Ensure that the bench top is
not in contact with machinery (especially centrifuges), or subject to
knocks.
4. Do not pick up the stand to read results as this will affect other
tests in progress. Bring the eye to the level of the top of the red
cells to read accurately from the scale.
5. Ensure you read the result of each test at exactly 1 hour from when
you set up the tube in the rack: remember the cells will go on
sedimenting after the first hour and results read at 75 minutes will
usually be higher than those read at 60 minutes. Use a laboratory timer
or alarm to remind you to read the results at the correct time.
References
1. ICSH recommendations for measurement of erythrocyte sedimentation rate.
International Council for Standardization in Haematology (Expert Panel on Blood
Rheology) J Clin Path. 1993; 46: 198 - 203.
2. Bain, B. Some influences on the ESR and the fibrinogen level in healthy
subjects. Clin Lab Haematol. 1983; 5: 45 - 54.
3. Miettinen AK, Heinonen PK, Laippala P, Paavonen J. Test performance of
ESR and C-reactive protein in assessing the severity of acute pelvic
inflammatory disease. Am J Obstet Gynaecol. 1993;
169:1143 - 1149.
4. Ponder, E. Sedimentation and Rouleaux formation. Quart J Physiol. 1925;
15: 236.
5. Manley, R. The effect of room temperature on ESR and its correction. J Clin
Path. 1957; 10: 354.
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