The erythrocyte sedimentation rate (ESR) is a blood test used to screen for inflammatory diseases and monitor treatment progress. It measures the rate at which red blood cells settle in the blood serum and is expressed in millimeters per hour. Abnormal rates can indicate inflammation, but cannot pinpoint its location or cause. Sedimentation rates can also be affected by drugs and are used in conjunction with other tests for diagnosis and monitoring.
The sedimentation rate may refer to a blood test formally known as the erythrocyte sedimentation rate (ESR). The sedimentation rate can also refer to the result of such a test. This test has been used extensively by physicians to screen for inflammatory diseases and to monitor the progress of treatment.
Erythrocytes are red blood cells. An ESR is a procedure that measures the rate at which red blood cells are deposited in the blood serum. To conduct the procedure, blood must be drawn and stored in a test tube. The tube must be left still and in an upright position. Eventually, the red blood cells will start to go downhill. The rate of sedimentation is found by observing the rate at which red blood cells go down in one hour.
While this is a fairly simple test, it’s usually done in a lab. The sedimentation rate is expressed in millimeters per hour, or mm/hour. There are sedimentation rates considered normal depending on age and gender. For example, the normal rate for females under 50 is generally 0-20 mm/h and for males under 50 it is 0-15 mm/h. These rates tend to be slightly elevated as you get older.
Sedimentation rates higher than normal may be an indicator of inflammation. For this reason, these tests have been used extensively by physicians who suspect conditions such as polymyalgia rheumatica and temporal arthritis. When the test accurately indicates inflammation, the rule of thumb is that the higher the rate, the more inflammation is likely to be present in the body.
ESR is a screening test, however, and is not recommended as a diagnostic tool. There are several reasons for this. For starters, while a sedimentation rate can indicate inflammation, it can’t pinpoint where the inflammation is or what’s causing it.
Also, an abnormal sedimentation rate can indicate numerous conditions, depending on the amount of variance. Higher than normal rates could be caused by conditions such as syphilis, tuberculosis or pregnancy. When rates are drastically higher than normal, the causes could be systemic infections, multiple myeloma, or necrotizing vasuclite. It’s also possible that the sedimentation rate is lower than normal, in which case congestive heart failure, sickle cell disease, or polycythemia could be the problem.
Drugs can affect sedimentation rates. For example, oral contraceptives and vitamin A can increase the rate, while aspirin and quinine can decrease it. For these reasons, an ESR is normally done in conjunction with other tests, such as comprehensive metabolic panels and rheumatoid factors.
Sedimentation rates can also be used for monitoring purposes. A person who has an elevated rate due to inflammation, for example, should find that the rate normalizes as the inflammation subsides. Stable or decreasing sedimentation rates may therefore be an indication of the effectiveness of a prescribed treatment.
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