The sedimentation rate (or erythrocyte sedimentation rate) is a test that measures that degree of inflammation occurring in the body. Inflammation is the sum total of the body’s reaction to infection, allergy, irritation, malignancy (cancer), or injury. The test is neither specific to a particular type of disease or condition, nor does it identify what tissues or organs are inflamed. In other words, while the sedimentation rate is a useful test to verify an impression of the possible presence of a particular illness, it cannot stand alone as a definitive diagnostic tool. The patient’s history and symptoms must be correlated with the sedimentation rate and other laboratory tests in order to arrive at a clinical diagnosis.
The sedimentation rate is literally a measure of the distance that red blood cells (erythrocytes) fall through a test tube filled with blood in an hour’s time. This process leaves clear plasma, devoid of red blood cells, at the top of the tube. When there is an inflammatory process occurring in the body, the body produces a variety of proteins that stick to red blood cells. These proteinred blood cell complexes are heavier than unaffected red blood cells, allowing them to fall more quickly and farther through the blood in the test tube. As a result, when inflammation is present in the body, the red blood cells drop through the test tube more quickly, and more of them accumulate at a lower part of the test tube, resulting in a higher sedimentation rate.
A sedimentation rate is usually done when an individual is having symptoms compatible with an inflammatory disorder, particularly polymyalgia rheumatica and temporal arteritis. Some symptoms that might prompt a practitioner to order a sedimentation rate include unexplained headache, joint pain or stiffness, anemia, unintentional weight loss, fevers, and severe fatigue. The sedimentation rate is also frequently used to monitor a disease process that has already been diagnosed, such as Hodgkin’s lymphoma, or autoimmune disorders such as rheumatoid arthritis or systemic lupus erythematosus.
The sedimentation rate is not diagnostic. This means that getting a specific result does not definitively confirm the presence of any particular disease.
Autoimmune disorder— A condition in which the body’s immune system is accidentally attacking tissues or organs of the body, causing injury and disease.
Inflammation— Pain, swelling, redness, and heat that often occurs when tissues of the body are injured, infected, or irritated in some way.
Malignancy— Conditions that are cancerous, meaning that they produce abnormal cells capable of invading and destroying other local and distant tissues.
Polymyalgia rheumatica— A condition with symptoms of achiness and stiffness, primarily striking older adults.
Temporal arteritis— A condition in which inflammation of the blood vessels that supply the head and neck result in severe, chronic headache, particularly over one temple, as well as fever, weight loss, and severe fatigue.
Instead, the test is used to correlate with the clinical picture, meaning the history and the symptoms that an individual is experiencing.
This test requires blood to be drawn from a vein (usually one in the forearm), generally by a nurse or phlebotomist (an individual who has been trained to draw blood). A tourniquet is applied to the arm above the area where the needle stick will be performed. The site of the needle stick is cleaned with antiseptic, and the needle is inserted. The blood is collected in vacuum tubes. After collection, the needle is withdrawn, and pressure is kept on the blood draw site to stop any bleeding and decrease bruising. A bandage is then applied.
There are no restrictions on diet or physical activity, either before or after the blood test.
As with any blood tests, discomfort, bruising, and/or a very small amount of bleeding is common at the puncture site. Immediately after the needle is withdrawn, it is helpful to put pressure on the puncture site until the bleeding has stopped. This decreases the chance of significant bruising. Warm packs may relieve minor discomfort. Some individuals may feel briefly woozy after a blood test, and they should be encouraged to lie down and rest until they feel better.
Basic blood tests, such as sedimentation testing, do not carry any significant risks, other than slight bruising and the chance of brief dizziness.
The normal sedimentation rate range in men is 0-15 mm/hour. The normal sedimentation rate range in women is 0-20 mm/hour. The normal sedimentation rate range in children is 0-10 mm/hour. The normal sedimentation rate range in newborn babies is 0-2 mm/ hr. Women normally have higher sedimentation rates than men. People over the age of 50 years also have higher normal sedimentation rates than do younger individuals. Other factors that may increase the sedimentation rate without suggesting the presence of disease include obesity or pregnancy.
An elevated sedimentation rate can be caused by a number of conditions, including an episode of crisis in sickle cell disease, osteomyelitis, stroke, prostate cancer, coronary artery disease, rheumatoid arthritis, chronic infections, certain cancers (including Hodgkin’s disease and renal cell carcinoma), ankylosing spondylitis, thyroid disease, temporal arteritis, scleroderma, polyarteritis nodosa, systemic lupus erythematosus, infections (appendicitis, osteomyelitis, pelvic inflammatory disease, pneumonia), and Kawasaki disease in children.
An extremely elevated sedimentation rate can be caused by multiple myeloma and polymyalgia rheumatica.
An abnormally low sedimentation rate can be caused by sickle cell anemia (not during painful crisis), use of steroid medications, polycythemia, or high serum glucose.
Goldman L, Ausiello D., eds. Cecil Textbook of Internal Medicine. 23rd ed. Philadelphia: Saunders, 2008.
Harris ED et al. Kelley’s Textbook of Rheumatology. 7th ed. Philadelphia: Saunders, 2005.
Hoffman R. et al. Hematology: Basic Principles and Practice. 4th ed. Philadelphia: Elsevier, 2005.
McPherson RA et al. Henry’s Clinical Diagnosis and Management By Laboratory Methods. 21st ed. Philadelphia: Saunders, 2007.
American Association of Clinical Chemistry. 1850 K St., N.W Suite 625, Washington, DC 20006. http://www.aacc.org.
National Institutes of Health. [cited February 10, 2008]. http://www.nlm.nih.gov/medlineplus/encyclopedia.html.
Rosalyn Carson-DeWitt, MD
Segmental resection seeSegmentectomy