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Definition
By Mayo Clinic staffSed rate, or erythrocyte sedimentation rate (ESR), is a blood test that can reveal inflammatory activity in your body. A sed rate test isn't a stand-alone diagnostic tool, but the result of a sed rate test may help your doctor diagnose or monitor an inflammatory disease.
Red blood cells, or erythrocytes (uh-RITH-ro-sites), are cells that transport oxygen throughout your body. When blood is placed in a glass test tube, as part of a sed rate test, red blood cells gradually settle to the bottom. Inflammation alters certain proteins of red blood cells, causing the cells to clump together. Because these clumps of cells are denser than individual cells, they settle to the bottom relatively quickly.
The sed rate test measures the distance red blood cells fall in a test tube in one hour. The distance indirectly measures the level of inflammation — the further the red blood cells have descended, the greater the inflammatory response of your immune system.
- Fischbach FT, et al. Manual of Laboratory and Diagnostic Tests. Online ed. Philadelphia, Pa.: Lippincott Williams & Wilkins; 2009. http://ovidsp.tx.ovid.com/spb/ovidweb.cgi?QS2=434f4e1a73d37e8ca2f1a384710471f9f1921ff2861d638048feb3298636e2121057526476519244483bb14807d4c5520d1933e4b30b7a9ea311cccda5cd88d5aa464a0044d1c124a7e8ef444bf0c63414596415eb6d902f34bcb1caedcb4cab3b1cd1ca991a5966a4ae4b95bc1fe1b52df6671229f737d120cb3699d1742eb900d1e2340e85ee8d2c1d575e9550b816826f1b1566312dd6f534c6ff066e4b8b703a6d55561e2c7bb41af5b1b2268df94e7ba28e509470ae52a3b105af7296a41ace23b8f7f517745d43f3660a827f57. Accessed Oct. 15, 2008.
- McPherson RA, et al. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa.: Saunders Elsevier; 2007. http://www.mdconsult.com/das/book/body/108738632-2/0/1393/0.html. Accessed Oct. 15, 2008.
- Brigden ML. Clinical utility of the erythrocyte sedimentation rate. American Family Physician. 1999;60(5):1443-50. http://www.aafp.org/afp/991001ap/1443.html. Accessed Oct. 15, 2008.
- Reference values. Sedimentation. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2008.
