Erythrocyte Sedimentation Rate

You are right, ESR is a non-specific test for inflammation. However it is easy to perform, widely available and inexpensive making it a widely used screening test for inflammation. It is also used a monitoring tool for response to treatment in conditions in which it is raised (tuberculosis, autoimmune diseases etc).

Basics:

The ESR test in performed in the laboratory by placing anticoagulated blood in an upright tube (Westegren's most often). At the end of an hour of this, the rate of the RBC sedimentation is measured.



Normal value:

ESR values tend to rise with age and are generally higher in women. ESR is also elevated in the black population and those with anemia.

A rule of thumb for calculating maximum normal ESR in a person is:
ESR (mm/hr) = {Age (in years) + 10 (if female) } /2

Mechanism:
ESR is determined by the interaction between factors that promote (fibrinogen) and resist sedimentation (negative charge of RBCs - that repel each other).

Increased rouleaux formation contributes to high ESR. Rouleaux are stacks of RBCs that become heavier and sediment faster. Increased plasma proteins contributes to increased rouleaux formation and thus ESR.



Some conditions with very high ESR:

1. Multiple myeloma (ESR often >100)
2. Connective tissue disorders (ESR often >100) - SLE, RA and other autoimmune diseases
3. Tuberculosis
4. Malignancies
5. Severe anemia

Some conditions with low ESR:

1. Polycythemia
2. Severe Leukocytosis
3. Sickle cell disease (anemia)
4. Hereditary spherocytosis

Please note that sickle cell anemia and spherocytosis have low ESR unlike other anemias. This is due to reduced rouleaux formation owing to the abnormally shaped RBCs in this condition.

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