Sedimentation rate is a blood test used to screen for underlying inflammation in the body. The test – also called erythrocyte sedimentation rate (ESR) or sed rate – measures the rate at which red blood cells (erythrocytes) separate from blood serum and fall to the bottom of a blood sample (sedimentation). It serves as a screening test for several different diseases.
Sed rate tests are interpreted based on what they reveal about the body’s blood cells. Inflammation changes the amount of proteins in the blood, causing blood cells to clump together and form sediment (the matter that settles at the bottom of blood) faster than they normally would. During a sed test, blood is drawn from a patient’s vein and placed in a test tube for laboratory analysis. After one hour, the distance traveled by red blood cells toward the bottom of the tube is measured in millimeters, revealing how long it takes the cells to settle.
The more red blood cells found at the bottom of the tube in sediment layer, the higher the level of proteins present. The liver and the immune system produce these proteins when the body has certain conditions such as infection, autoimmune diseases or cancer. Inflammation, pregnancy and aging can also elevate sedimentation rates. In addition to helping diagnose the presence of a disease, sed tests can be used to monitor the course of the disease and the effectiveness of treatment.
Sedimentation tests may be used to rule out other conditions when asthma or allergies are suspected.
About sedimentation rate
A sedimentation rate (sed rate) blood test measures how fast red blood cells (erythrocytes) settle in a test tube in one hour. Also known as erythrocyte sedimentation rate tests, sed rate tests do not diagnose diseases, but are a screening procedure that can suggest or be used to monitor inflammatory or malignant diseases. Further testing is necessary to determine a diagnosis.
Sed tests can help uncover underlying disease when symptoms are vague or physical examination does not offer conclusive results. For example, a person with hives may have a sed test that reveals an underlying infection that is causing the symptoms.
Sed rates that are too high can indicate the presence of a disease or abnormality in the body. Although the test can indicate the presence of disease, it cannot determine where the inflammation is present or which disease is causing it. Results of the test can also be affected by conditions other than inflammation. Therefore, the sed rate has been replaced by more specific tests for many of the conditions for which it was once used. However, there are still several conditions for which the sed rate test is used in conjunction with other diagnostic tools (e.g., imaging tests) and a patient’s medical history, to help make a diagnosis. These include infections, inflammatory and autoimmune diseases and cancer.
Sedimentation tests may be used to rule out other conditions when asthma or allergies are suspected.
Sed rate tests carry few risks. There may be some discomfort associated with the insertion of the needle into the arm. However, this pain should be minor, such as prick or stinging sensation, and last only briefly. Other potential risks involved in the testing include:
- Blood accumulating under the skin (hematoma)
- Excessive bleeding
- Fainting or lightheadedness
- Multiple punctures to locate veins
Before, during and after the sedimentation rate test
Patients need to take very few preparatory steps prior to most blood testing. Patients may need to reduce or stop certain medications at some point prior to the test. Additionally, food intake as well as exercise may be temporarily restricted or suspended. Alcohol and caffeine should be avoided prior to a blood test. Physicians will provide information about dietary restrictions or other necessary preparatory measures in advance of the test.
Sed rate tests are performed in a physician’s office or other medical facility. The process of collecting the blood sample for analysis usually takes only a few minutes.
On the day of the sedimentation test, the procedure will be explained and patients will have the opportunity to ask questions. The medical professional will also ask questions about the patient’s medical history to determine if the patient is taking any medications that will interfere with the test’s accuracy or has any history of clotting problems.
The test administrator will then clean the puncture site – usually the inside of the elbow or the back of the hand – with alcohol. An elastic band will be placed around the upper arm. This applies pressure and restricts blood flow through the veins above the tourniquet, causing blood to pool in the veins of the lower arm.
A needle is inserted into the vein at the puncture site, and a small sample of blood is collected in an air-tight vial or a syringe. Before the needle is withdrawn, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and pressure is applied at the puncture site to facilitate blood clotting. The blood sample is then sent to a laboratory for analysis.
The procedure is slightly different for infants and young children. In such cases, the area will be cleansed with alcohol and a sharp needle or lancet (pointed surgical knife) will be used to puncture the skin. Blood will rise to the surface of the skin and the healthcare provider will collect a sample in a pipette (a glass tube), on a slide, on a test strip or into a small container. Pressure may be applied if there is any continued bleeding.
Understanding sedimentation rate test results
After one hour, the rate at which red blood cells have settled at the bottom of the test tube is measured in millimeters per hour (mm/hr). Results will be measured against the following normal values (which can vary slightly from lab to lab):
|Gender/Age Group||Normal Sed Rate Value|
|Males under 50||0 to 15 mm/hr*|
|Males over 50||0 to 20 mm/hr|
|Females under 50||0 to 20 mm/hr|
|Females over 50||0 to 30 mm/hr|
|Children||3 to 13 mm/hr|
|Newborns||0 to 2 mm/hr|
High sedimentation rates (sed rates) may indicate the following diseases:
- Arthritis. This includes psoriatic arthritis, rheumatoid arthritis and reactive arthritis, a form of the disease that occurs as a reaction to infection elsewhere in the body and may cause painful skin rashes.
- Giant cell arteritis. Inflammation of the lining of the arteries that may cause tenderness of the scalp.
- Raynaud’s phenomenon. Disorder that affects the blood vessels in the fingers, toes, ears and nose and causes changes in skin color and sensation.
- Relapsing polychondritis. Condition characterized by painful, destructive inflammation of cartilage and other connective tissues. It may result in a variety of skin rashes.
- Scleroderma. An autoimmune condition characterized by hardening and thickening of the skin.
- Sjögren syndrome. An immune system disorder that causes dry eyes and dry mouth. In some cases, dry skin (xerosis) or rashes also are present.
- Systemic lupus erythematosus. Autoimmune disease that that leads to the inflammation of and damage to body tissues. Some patients experience a skin rash that affects the face.
- Temporal arteritis. A vascular disease involving inflammation and damage to the blood vessels, particularly the large or medium arteries that branch from the external carotid artery of the neck.
- Blood, lymph and bone marrow cancers (e.g., leukemia, lymphoma, myeloma) and cancers that have spread (metastasized) to the lungs, kidneys, breast or colon.
High sed rates may also indicate a number of infections including pneumonia (inflammation of the lungs caused by an infection), pelvic inflammatory disease (bacterial infection of a woman’s reproductive organs), syphilis (a sexually transmitted disease caused by bacteria) and tuberculosis (an infectious disease that affects the lungs, and can spread to other organs) as well as infections of the skin, kidney, bone, joint or heart valve. They may also indicate conditions such as pregnancy, preeclampsia (pregnancy-induced high blood pressure), thyroid disease and chronic kidney failure.
Low sed rates can also signal disease or abnormality, including:
- Sickle cell anemia (a condition characterized by abnormalities of the red blood cells, resulting in chronic pain)
- Polycythemia (elevated production of red blood cells)
- Hyperglycemia (increased blood sugar levels)
- Heart failure and other heart conditions
- Hyperviscosity (slowing of newborn’s blood flow due to excessive red blood cell count)
- Low plasma protein (due to liver or kidney disease)
- Hypofibrinogenemia (decreased fibrinogen levels)
It is important to note that sed tests alone cannot diagnose these conditions (or any specific problem), but merely indicate the presence of disease or another abnormality in the body. Although this sensitive test can indicate the presence of disease, it cannot determine which disease is present. Further testing will be necessary to confirm any diseases that are suspected.
Factors that impact sedimentation rate test results
There are a number of factors that can potentially skew the results of a sedimentation rate (sed rate) test. These include:
- Not drawing blood within one minute after the tourniquet has been applied to the arm.
- Waiting too long to check the blood sample. Samples should be checked within three hours of being drawn.
- Changes in thyroid levels and other hormones. Certain hormone disorders, such as thyroid disease, may mildly increase the sed rate.
- Changes in female sex hormones. Women may have elevated sedimentation rates during pregnancy and menstruation.
- Obesity (a body mass index of 30 or greater).
- Hepatitis (inflammation of the liver).
- Anemia (red blood cell deficiency).
- Medications or supplements, including:
- Nonsteroidal anti-inflammatory drugs (NSAIDS), such as aspirin
- Anticoagulants (prevent blood clots)
- Birth control pills
- Antiarrhythmics (treat abnormal heart rhythms)
- Theophylline (treats asthma and other lung diseases)
- Vitamin A
- Antimalarial agents (treat malaria)
- Disease-modifying antirheumatic drugs (DMARDs, decrease or stop joint damage)
- Selective estrogen receptor modulators (SERMs, treat and help prevent breast cancer)
- Anticonvulsants (help prevent seizures)
Questions for your doctor on sedimentation rate
Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions regarding the sedimentation rate test:
- Why are you recommending that I undergo this blood test? What conditions are you concerned about?
- Can you explain the test to me in detail?
- Are there special preparations I need to make before the test? Do I need to fast? Should I stop taking any of my medications for a period before testing?
- Will I feel any pain before or after the blood is drawn?
- How long will it take for the results to be available? Will you call me when they are in?
- How accurate is this test? Can I trust the results?
- If my sed rate is elevated, what further testing may you recommend?
- What do my results indicate?
- Will you be prescribing medication based on the results?
- Will I need sed rate testing on a regular basis to monitor any conditions or factors related to my medications?