By Mayo Clinic staff
Sed 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.
Why it’s done
Your doctor may order a sed rate test to help make a diagnosis, judge the effectiveness of a treatment or assess the severity of certain inflammatory diseases.
If you have symptoms of certain inflammatory disorders, a sed rate test may help your doctor consider a diagnosis. Sed rate tests were used more frequently in the past than they are today because more-specific measures of inflammatory activity are available. Today, the test is most often used if your doctor suspects you have one of the following diseases:
- Rheumatoid arthritis, which causes inflammation of the lining of joints and results in pain, joint damage and joint deformity
- Polymyalgia rheumatica, an inflammatory disorder that causes widespread muscle aching and stiffness, primarily in your neck, shoulders, upper arms, thighs and hips
- Giant cell arteritis (GCA), or temporal or cranial arteritis, an inflammation of the lining of your arteries that can cause headaches, jaw pain, and blurred or double vision
If you’re taking medications, such as corticosteroids, to treat rheumatoid arthritis or another inflammatory disease, your doctor may order a sed rate test to monitor the effect of the treatment. Although improvements in your symptoms will likely be the primary measure of a drug’s effect, changes in your sed rate may help your doctor monitor your response to treatment.
Use in emergency rooms
A sed rate test may be used in an emergency room to add to the evidence of an infectious or inflammatory condition, such as pneumonia, appendicitis or another acute inflammatory disease.
How you prepare
The sed rate is a simple blood test. You won’t need to fast before the test, but you should avoid a high-fat meal, which could obscure the results of the test.
What you can expect
A nurse or medical assistant will use a needle to draw blood from a vein, most likely a vein in your arm. The site on your arm may be tender for a few hours, but you’ll be able to resume most normal activities.
Results from your sed rate test will be reported in the distance in millimeters (mm) red blood cells have descended in one hour. The normal range is 0-22 mm/hour for men and 0-29 mm/hour for women. The upper threshold for a normal sed rate value may vary somewhat from one medical practice to another.
The results of your sed rate test are one piece of information to help your doctor assess your health. Talk to your doctor about what your sed rate results mean in light of the symptoms you’re experiencing and the results of other diagnostic tests.
Accuracy of test results
A number of conditions can affect the properties of blood, thereby affecting how quickly red blood cells sink in a sample of blood. Therefore, information about inflammatory disease — what your doctor intends to learn from the sed rate test — may be obscured by the influence of other conditions. These complicating factors include:
- Heart disease
Your doctor will take into account possible complicating factors when interpreting the results of your sed rate test.
Source: Mayo Health Clinic.com, November 2010