What Is a Sedimentation Rate (Sed Rate)?
A sedimentation rate is a common blood test that is used to detect and monitor inflammation in the body. The sedimentation rate is also called the erythrocyte sedimentation rate because it is a measure of the speed that the red blood cells (erythrocytes) in a tube of blood fall to the bottom of the tube (form sediment). Sedimentation rate is often abbreviated as sed rate or ESR.
What Are the Reasons for Performing a Sedimentation Rate Test?
Doctors use the sedimentation rate to help to determine if inflammation is present in the patient. Additionally, the sedimentation rate can be a convenient method of monitoring the progress of treatment of diseases that are characterized by inflammation. Accordingly, a high or elevated sedimentation rate would correlate with more disease activity while a low sedimentation rate would suggest that the disease is less active.
Examples of diseases that are commonly monitored with the sedimentation rate test include
Who Performs a Sedimentation Rate Test?
The sedimentation rate is typically measured in a laboratory that does testing of blood samples. The sedimentation rare is ordered by any health-care professionals who are determining whether or not inflammation is present, and/or to what degree.
How Is a Sedimentation Rate Test Performed?
A sedimentation rate is performed by measuring how long it takes red blood cells (RBCs) to settle in a test tube. The RBCs become sediment in the bottom of the test tube over time, leaving the blood serum visible above. The classic sedimentation rate test is typically performed in a calibrated narrow tube. The sedimentation rate is measured simply by recording how far the top of the RBC layer has fallen (in millimeters) from the top of the serum layer in one hour. The sedimentation rate increases when more inflammation is present in the body of the person whose blood was sampled because inflammation alters certain substances on the surfaces of the red blood cells, making them tend to adhere together and more rapidly fall to the bottom of the test tube.
What Are Normal Sedimentation Rates?
The normal sedimentation rate (Westergren method) for males is 0-15 millimeters per hour, for females it is 0-20 millimeters per hour. The sedimentation rate can be slightly elevated in the elderly. Falsely low sedimentation rates can occur in the blood from people with leukemia or polycythemia rubra vera.
Firestein, Gary S., et al. Kelley & Firestein's Textbook of Rheumatology, 10th Ed. China: Elsevier, 2016.