Sedimentation Rate Test
Sedimentation Rate Test
The sedimentation rate test, also called the erythrocyte sedimentation rate (ESR) or sed rate test, measures the speed at which the red blood cells (erythrocytes or RBCs) separate from the liquid part of the blood (plasma) and settle to the bottom in a tube of anticoagulated blood.
The sedimentation rate is a non-specific indicator of the presence of inflammation or infection. Although newer methods for diagnosing specific diseases have decreased the test's usefulness, it is still an important tool for the diagnosis and monitoring of two diseases: polymyalgia rheumatica and temporal arteritis. Sedimentation rate testing at regular intervals can also be helpful in predicting relapse in patients with chronic diseases such as Hodgkin's disease and other cancers.
Patients who have bleeding disorders or are taking blood thinners might have trouble with bleeding following a venipuncture. Before having a blood sample drawn, such patients should tell the phlebotomist about their condition.
The sedimentation rate test dates back to the early 1900s. In 1921, Westergren introduced a new method for performing the test that has become the time-honored classic. It is the recommended method of the International Committee for Standardization in Haematology and the National Committee for Clinical Laboratory Science. While automated methods can perform the sed rate in less time and with smaller samples of blood, many labs continue to use the Westergren method because it is simple and inexpensive.
For accurate results, the blood sample should be fresh (within two hours of collection is best). The sample might be rejected because it is too old or because the collection tube is underfilled, not labeled correctly, or contains blood that is hemolyzed or clotted.
The standard Westergren method includes the following steps:
- Diluting whole blood, or blood anticoagulated with EDTA, in citrate (1 volume of citrate to 4 volumes of blood).
- Aspirating the diluted blood to the 200 mm mark of a Westergren tube (30 cm in length and 2.55 mm in diameter with a uniform bore diameter) by means of a mechanical device or teat.
- Placing the tube in a vertical position in a Westergren rack in a location that is free of vibration and that is not exposed to direct sunlight.
- After exactly one hour, reading the distance the erythrocytes have fallen, and recording this value as the sedimentation rate.
This test requires no special preparation.
To prevent bruising, pressure should be applied to the site of the venipuncture as soon as the needle is withdrawn. Pressure should be maintained until the bleeding stops.
No complications are associated with this test other than the possibility of having a slight bruise from having blood drawn from a vein. In very rare cases, vein inflammation or continued bleeding at the puncture site might be a problem.
The sedimentation rate is measured in millimeters per hour (mm/hr). Normal values vary with age and sex, and can vary from lab to lab. A normal result does not rule out a diagnosis of inflammatory disease. An abnormal result does not diagnose any specific disease, and should be evaluated in conjunction with the patient's physical exam, medical history, and other more specific blood tests. In general, an abnormal result correlates with active inflammatory disease, and the sedimentation rate test is a useful way of monitoring disease progression or treatment. If the result is abnormal, the test should be repeated to verify its accuracy. A number of factors (such as medications, hormones, obesity, and improper collection or handling of the blood sample) can affect the outcome of this test.
- Males under 50: 0 to 15 mm/hr.
- Males 50 and older: 0 to 20 mm/hr.
- Females under 50: 0 to 20 mm/hr.
- Females 50 and older: 0 to 30 mm/hr.
- Children: 3 to 13 mm/hr.
- Newborns: 0 to 2 mm/hr.
Greater than normal values
A greater than normal value can indicate inflammation due to infection, autoimmune disease (such as rheumatoid arthritis), or certain types of cancer (such as multiple myeloma and Hodgkin's disease). An elevated sed rate usually occurs when the level of plasma proteins in the blood is higher than normal. These plasma proteins (primarily fibrinogen) bind to the red blood cells, reducing the negative surface charge which normally causes the cells to repel each other. The red blood cells stack and settle to bottom of the tube faster than single red blood cells.
Lower than normal values
A lower than normal value can indicate diseases such as congestive heart failure, sickle cell anemia, and polycythemia (abnormally high numbers of circulating red blood cells).
Health care team roles
A phlebotomist usually draws and labels the blood sample for the sedimentation rate. However, any health care professionals trained in phlebotomy (such as doctors, nurses, clinical laboratory scientists, or medical technologists) can perform this task.
When the blood sample arrives at the lab, a clinical laboratory scientist (CLS [NCA]), medical technologist (MT [ASCP]), clinical laboratory technician (CLT [NCA]), or medical laboratory technician (MLT [ASCP]) will set up the test and record the sedimentation rate after the specified period of time, usually one hour.
Arteritis— The inflammation of an artery.
Aspirate (verb)— To draw or move by suction.
Phlebotomist— A person who draws blood from a vein.
Phlebotomy— A procedure in which a vein is punctured to obtain a blood sample.
Polymyalgia rheumatica— A disease that causes aching and stiffness in the neck, shoulder, or pelvis.
Temporal (giant cell) arteritis— A disease caused by arterial inflammation that usually results in headaches and facial pain. The production of giant cells is characteristic of this type of arteritis. If the ophthalmic artery and its branches become involved, it can also cause blindness.
Venipuncture— The puncture of a vein to withdraw a blood sample.
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