Sedimentation Rate Overview
A sedimentation rate is common blood test that is used to detect and monitor inflammation in the body. The sedimentation rate is also called the erythrocyte sedimentation rate because it is a measure of the speed that the red blood cells (erythrocytes) in a tube of blood fall to the bottom of the tube, or sediment. Sedimentation rate is often abbreviated as sed rate or ESR.
Doctors use the sedimentation rate to help to determine if inflammation is present in the patient. Additionally, the sedimentation rate can be a convenient method of monitoring the progress of treatment of diseases that are characterized by inflammation. Accordingly, a high sedimentation rate would correlate with more disease activity while a low sedimentation rate would suggest that the disease is less active.
Examples of diseases that are commonly monitored with the sedimentation rate test include:
Sedimentation Rate Test
A sedimentation rate is performed by measuring how long it takes red blood cells (RBCs) to settle in a test tube. The RBCs become sediment in the bottom of the test tube over time, leaving the blood serum visible above. The classic sedimentation rate test is typically performed in a calibrated narrow tube. The sedimentation rate is measured simply by recording how far the top of the RBC layer has fallen (in millimeters) from the top of the serum layer in one hour. The sedimentation rate increases when more inflammation is present in the body of the person whose blood was sampled because inflammation alters certain substances on the surfaces of the red blood cells, making them tend to adhere together and more rapidly fall to the bottom of the test tube.
Normal Sedimentation Rates
The normal sedimentation rate (Westergren method) for males is 0-15 millimeters per hour, for females it is 0-20 millimeters per hour. The sedimentation rate can be slightly elevated in the elderly. Falsely low sedimentation rates can occur in the blood from persons with leukemia or polycythemia rubra vera.
Medically reviewed by Martin E. Zipser, MD; American board of Surgery
Medically Reviewed by a Doctor on 6/25/2014
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