Sedimentation Rate (Sed Rate)
The sedimentation rate (sed rate) blood test measures how quickly red blood cells (erythrocytes) settle in a test tube in one hour. The more red cells that fall to the bottom of the test tube in one hour, the higher the sed rate.
When inflammation is present in the body, certain proteins cause red blood cells to stick together and fall more quickly than normal to the bottom of the tube. These proteins are produced by the liver and the immune system under many abnormal conditions, such as an infection, an autoimmune disease, or cancer.
There are many possible causes of a high sedimentation rate. For this reason, a sed rate is done with other tests to confirm a diagnosis. After a diagnosis has been made, a sed rate can be done to help check on the disease or see how well treatment is working.
Why It Is Done
A sed rate test is done to:
- Find out if inflammation is present.
- Check on the progress of a disease.
- See how well a treatment is working.
How To Prepare
In general, there's nothing you have to do before this test, unless your doctor tells you to.
How It Is Done
A health professional uses a needle to take a blood sample, usually from the arm.
How long the test takes
The test will take a few minutes.
How It Feels
When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.
There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
Some diseases that cause inflammation don't increase the sed rate, so a normal sed rate doesn't always rule out a disease.
There are many possible causes of a high sed rate. For this reason, the test is done with other tests to confirm a diagnosis.
Results are usually available right away.
High sed rates may be caused by:
- Autoimmune diseases, such as systemic lupus erythematosus or rheumatoid arthritis.
- Cancer, such as lymphoma or multiple myeloma.
- Chronic kidney disease.
- Infection, such as pneumonia, pelvic inflammatory disease, or appendicitis.
- Inflammation of joints (such as polymyalgia rheumatica) and blood vessels (such as giant cell arteritis).
- Inflammation of the thyroid gland (Graves' disease).
- Kidney, bone, joint, skin, or heart valve infections.
- Pregnancy and preeclampsia (toxemia of pregnancy).
- Viral infections.
Low values may be caused by:
Current as of: June 17, 2021
Author: Healthwise Staff
Anne C. Poinier MD - Internal Medicine
Martin J. Gabica MD - Family Medicine
E. Gregory Thompson MD - Internal Medicine
Kathleen Romito MD - Family Medicine
Adam Husney MD - Family Medicine