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What is the Sedimentation Rate?

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  • Written By: Felicia Dye
  • Edited By: Heather Bailey
  • Last Modified Date: 19 September 2016
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Sedimentation rate can refer to a blood test formally known as erythrocyte sedimentation rate (ESR). Sedimentation rate can also refer to the result of such a test. This test has been widely used by doctors to screen for inflammatory diseases and to monitor the progress of treatment.

Erythrocytes are red blood cells. An ESR is a procedure that measures how fast red blood cells become sediment in blood serum. To conduct the procedure, blood needs to be drawn and stored in a tube. The tube needs to be left still and in an upright position. Eventually, the red bloods cells will begin to descend. The sedimentation rate is gathered by noting how fast the red blood cells descend in an hour.

Although this is a fairly simple test, it is usually conducted in a laboratory. The sedimentation rate is expressed as millimeters per hour, or mm/hr. There are sedimentation rates that are considered normal depending upon age and sex. For example, the normal rate for females under 50 is generally 0-20 mm/hr and for males under 50 it is 0-15 mm/hr. These rates tend to be slightly elevated with advanced age.

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Above normal sedimentation rates can be an indicator of inflammation. For this reason, these tests have been widely used by physicians who suspect conditions such as polymyalgia rheumatica and temporal arthritis. When the test accurately indicates inflammation, the rule is that the higher the rate, the more inflammation that is likely to be present in the body.

ESR is a screening test, however, and is not advised as a diagnostic tool. There are several reasons for this. To begin with, although a sedimentation rate may indicate inflammation, it cannot pinpoint where the inflammation is or what is causing it.

Furthermore, an abnormal sedimentation rate can indicate numerous conditions, depending on the amount of variance. Above normal rates could be caused by conditions such as syphilis, tuberculosis, or pregnancy. When the rates are drastically higher than normal, the causes could be systemic infection, multiple myeloma, or necrotizing vasuclitis. It is also possible for the sedimentation rate to be below normal, in which case, the problem could be congestive heart failure, sickle cell anemia, or polycythemia.

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 conducted 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 the rate normalizes when the inflammation decreases. Stable or decreasing sedimentation rates can, therefore, be an indication of the effectiveness of a prescribed treatment.

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