Sedimentation Rate

Test Overview

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. Once 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 sedimentation rate (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

You do not need to do anything before you have this test.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form (What is a PDF document?).

How It Is Done

The health professional drawing blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Apply a gauze pad or cotton ball over the needle site as the needle is removed.
• Apply pressure to the site and then a bandage.

How It Feels

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Risks

Blood test

There is very little chance of a problem from having a blood sample taken from a vein.

• You may get a small bruise at the puncture site. You can reduce the risk of bruising by keeping pressure on the site for several minutes after the needle is withdrawn.
• In rare cases, the vein may become inflamed after the blood sample is taken. This condition is called phlebitis and is usually treated with a warm compress applied several times daily.
• Continued bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medications can also make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medication, tell your health professional before your blood is drawn.

Results

The sedimentation rate (sed rate) blood test measures how quickly red blood cells (erythrocytes) settle in a test tube.

Normal

Normal values may vary from lab to lab. Results are usually available right away.

High values

High sedimentation 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 toxemia of pregnancy.
• Viral infections.

Low values

Low values may be caused by:

• High blood sugar levels.
• Polycythemia.
• Sickle cell disease.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

• Pregnancy.
• Anemia.
• Having your menstrual period.
• Age. Sed rates normally increase with age.
• Medicines. Many medicines can change the results of this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.

What To Think About

• Even though some problems, such as giant cell arteritis, almost always cause a high sedimentation rate (sed rate), the test cannot be used by itself to identify a specific disease. Results of a sed rate test are considered along with your symptoms, other test results, and medical information.
• Some diseases that cause inflammation do not increase the sed rate, so a normal sed rate does not always rule out a disease.
• Some doctors use the C-reactive protein (CRP) blood test instead of the sed rate test to help identify inflammatory conditions. For more information, see the medical test C-Reactive Protein (CRP).

References

Other Works Consulted

• Handbook of Diagnostic Tests (2003). 3rd ed. Philadelphia: Lippincott Williams and Wilkins.

• Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.

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