Re: What exactly does Erythrocyte Sedimentation Rate test for and how?

The ESR, or "Erythrocyte Sedimentation Rate" assays the rate at which red blood cells sediment in a tube of anticoagulated blood. The test is used as an indication of underlying inflammatory processes. However, it is not *specific* for any particular disease or disease process. Per the pocket medical book, Bakerman's ABC's of Interpretive Laboratory Data, 1994 (ISBN 0-945577-06-0):

An increased ESR is caused by enhanced erythrocyte aggregation; this is caused by increased levels of asymmetrical macro-molecules, principally fibrinogen and the globular proteins in the blood. Normally, red blood cells have a negative charge on their surface; the like chares on red cells cause these cells to repel each other. Plasma proteins, especially fibrinogen, tend to adhere to the red cell membrane and neutralize the surface charges and make the cells more likely to aggregate, forming stacks or rouleaux. The aggregated (stacked) cells have a higher rate of mass to surface area than single cells and, therefore, will fall out from the plasma more readily.

Patients with giant cell arteritis often have an elevated ESR due to the inflammation of medium and small-sized arteries, primarily of those in the head. However, patients can present with this disease and have a normal ESR. As always, it's important to correlate laboratory information with clinical findings.

Hope this helps..

-L. Bry, M.D./PhD
Resident, Department of Pathology
Brigham & Women's Hospital
Harvard Medical School