Mark Oren, M.D., FACP
Sedimentation rate, also called erythrocyte sedimentation rate (ESR) or sed rate, is a type of blood test used to identify the presence of inflammation somewhere in the body. The test measures the rate at which red blood cells (erythrocytes) separate from blood plasma, the liquid component of blood in which blood cells are suspended.
Sed rate blood tests are not used to diagnose a specific disease or condition, but rather serve as a screening tool for many different conditions and diseases, including:
- Cancers, including blood cancers
- Autoimmune disorders such as rheumatoid arthritis and lupus
Patients need to take very few preparatory steps prior to a sed rate blood test, but are advised to follow any instructions provided by their physician. Sed rate blood tests are quick, simple and relatively inexpensive. They pose few risks, and most people who undergo them experience only slight to moderate pain or discomfort.
During a sed rate test, blood is drawn from a patient’s vein and placed in a test tube. 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. Sed rate blood tests are interpreted based on what they reveal about the environment surrounding the body’s blood cells. The more red blood cells found at the bottom of the tube, the higher the level of proteins present in the plasma. The liver and the immune system produce these proteins when the body has a sickness such as an infection, autoimmune disease or cancer. In addition to helping diagnose the presence of a disease, sed rate tests can be used to monitor the course of the disease and the effectiveness of treatment.
About sedimentation rate tests
A sedimentation rate (sed rate) blood test measures how quickly red blood cells settle at the bottom of a test tube within an hour after being drawn from a patient. An elevated sed rate indicates the presence of disease or inflammation somewhere in the body.
When inflammation is present in the body, proteins produced by the liver and immune system cause red blood cells to stick together. When blood is placed in a test tube, these clumps of cells fall more quickly to the bottom of the test tube than they would if they fell individually. Anemia can also result in a higher sedimentation rate because there are fewer red blood cells to drop to the bottom of the test tube.
Sed rate blood tests are not used to diagnose a specific disease or condition, but are used as a screening tool to detect whether inflammation is present in the body. Many different conditions or diseases may cause such inflammation, including:
- Cancers, including blood cancers
- Autoimmune diseases such as rheumatoid arthritis (RA) and lupus. Sed rate blood tests are often used to stage disease (identify the stage of disease development) in patients with RA.
- Other medical conditions, such as kidney failure, thyroid disease or toxemia of pregnancy.
Sed rate blood tests are an important component of diagnosing polymyalgia rheumatica (which causes muscle pain in the shoulder and hip areas) and temporal arteritis (inflammation of arteries of the head and neck that can cause headaches and a type of stroke and blindness). These conditions may appear independently or coexist in a patient. Sed rate test results are often significantly elevated in patients with either of these conditions.
Sed rate blood tests may be useful when symptoms are vague, or when a physical examination does not offer conclusive results.
Sed rate blood tests are quick, simple and relatively inexpensive. They pose few risks, and most people who undergo them experience slight to moderate pain or discomfort. Although the sed rate blood test may indicate the presence of disease, it cannot determine which disease is present. Therefore, the use of the sed rate test has been replaced over time by more specific tests. However, there are still several conditions for which the sed rate blood test is used (often in conjunction with other tests) to help make a diagnosis. These include infections, cancers, Autoimmune diseases and other disorders.
Before, during and after the blood test
Patients need to take very few preparatory steps prior to a sedimentation rate (sed rate) blood test. There are usually no food or fluid restrictions prior to a sed rate test. However, patients are advised to follow any preparatory instructions provided by their physician (e.g., to reduce or stop certain medications). In general, alcohol and caffeine should be avoided prior to a blood test.
On the day of the sed rate blood test, a patient may be asked questions about their medical history and whether they are taking any medications that may interfere with the test’s accuracy. A patient may specifically be asked about any history of blood clotting problems prior to the test.
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 arm.
A needle is inserted into the vein and the blood is collected in an airtight 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 to stop any bleeding at the site.
Because the size of veins can differ from person to person, the ease with which a blood sample can be obtained may differ in patients.
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 device) 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 in a small container. Pressure may be applied at the puncture site if there is any continued bleeding. Patients may feel slight to moderate pain while the blood is being drawn, and may experience some bruising and/or throbbing at the puncture site or lightheadedness afterwards. Warm compresses applied to the area may alleviate any discomfort. There is also a slight risk of infection anytime a person’s skin is broken, including during a blood test.
Factors that may affect test results
There are many different factors that can potentially skew the results of a sedimentation rate (sed rate) blood test. These factors include:
- Various technical factors during testing. Clotting of the blood sample, inadequate mixing, or vibration during testing may all affect sed rate test results. Not drawing blood within one minute after a tourniquet has been applied to the patient’s arm, or waiting too long to check a blood sample can also affect test results.
- Advanced age, because sedimentation rates generally increase over time.
- Changes in female sex hormones. Women tend to have higher sedimentation rates than men, and a woman’s sedimentation rate may be elevated during pregnancy or menstruation. The sed rate blood test was originally developed in the 1900s as a pregnancy test. However, the test proved to be inaccurate for that purpose and is now used as a nonspecific marker for disease.
- Changes in thyroid levels and levels of other hormones. Certain hormonal disorders, such as thyroid disease, may mildly increase the sedimentation rate.
- The use of certain medications or supplements, including:
- Tamoxifen. Treats and helps prevent breast cancer.
- Methotrexate. Treats a variety of cancers.
- Birth control pills.
- Iron or vitamin A supplements.
- Migraine medications.
- Antihypertensives. Medications used to treat high blood pressure.
- Bronchodilators. Medications that widen breathing passages.
- Thiazide diuretics. Medications that promote the formation of urine in the kidneys, causing the body to flush out excess fluids and minerals.
- Antibiotics. Medications that harm or kill microorganisms and are commonly used to treat infections.
Several other factors may affect sed rate test results, although there is some question as to whether their effect is clinically significant. These factors include obesity, body temperature and the use of nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin.
Understanding sedimentation rate test results
One hour after a patient’s blood sample has been placed in a test tube, the sedimentation rate (sed rate) is measured in millimeters per hour (mm/hr). This is the speed with which red blood cells in the blood settle at the bottom of the test tube.
Sed rate test results are then measured against the following normal values (which can vary slightly from lab to lab):
|Gender/Age Group||Normal Sed Rate Value|
|Males under 50||Under 15 mm/hr|
|Males over 50||Under 20 mm/hr|
|Females under 50||Under 20 mm/hr|
|Females over 50||Under 30 mm/hr|
|Children||3 to 13 mm/hr|
|Newborns||0 to 2 mm/hr|
High sedimentation rates may indicate the following conditions or diseases:
- Cancer, especially:
- Hodgkin’s disease
- Multiple myeloma
According to the American Academy of Family Physicians, a sedimentation rate of 100 mm/hr usually indicates cancer that has metastasized (spread to other areas of the body) in patients with solid tumors. Elevated sed rate levels may indicate early relapse in patients with Hodgkin’s disease.
- Infections, such as pneumonia, syphilis and tuberculosis
- Autoimmune diseases such as rheumatoid arthritis and lupus
- Kidney disease
- Thyroid disease
- Severe anemia
Low sedimentation rates can also signal disease or abnormality, including:
- Sickle cell anemia (in which red blood cells become crescent-shaped)
- Polycythemia (elevated production of red blood cells)
- Congestive heart failure
- Hyperviscosity (slowing of newborn’s blood flow due to excessive red blood cell count)
- Liver or kidney disease (in which production of plasma protein is decreased)
- Hypofibrinogenemia (decreased levels of fibrinogen, a blood plasma protein important to blood clotting)
It is important to note that sed rate blood tests cannot diagnose these conditions. An elevated sed rate indicates the presence of disease or inflammation somewhere in the body, but does not indicate which disease is present. Further testing, including additional types of blood tests, may be necessary to confirm suspected diseases. In a small number of cases, no cause for an elevated sed rate can be identified.
Questions for your doctor on sedimentation rate and cancer
Preparing questions in advance can help patients have more meaningful discussions with health care professionals regarding their condition. Patients may wish to ask their doctor the following questions related to sedimentation rate (sed rate) blood tests:
- Why is a sed rate test being recommended for me?
- What can this test tell me about my cancer condition?
- How should I prepare for the test?
- Are there any risks associated with this test?
- How long will I have to wait for test results? Who will explain these to me?
- What do my test results show?
- Will I need additional testing to confirm your diagnosis? How do I prepare for these tests?
- Will I need periodic sed rate tests to monitor my condition?
- If my blood work shows I need treatment, what are my options?