What Is an Erythrocyte Sedimentation Rate (Sed Rate)?

What to expect when undergoing this test

An erythrocyte sedimentation rate, commonly referred to as a sed rate, is a blood test that detects nonspecific inflammation in your body. An elevated (abnormally high) sed rate does suggest that there is an ongoing inflammatory process in your body, but does not indicate where or why. Your doctor may order this test to help come to diagnoses such as rheumatoid arthritis or lupus, to monitor diseases such as cancer, or other reasons.

Purpose of Test

When there's inflammation in your body, this is your immune system's response to a precipitating factor such as an infection, disease, or injury. The inflammation can be short-term, as in the case of an infection, or it can be long-term, as with a chronic disease.

A sed rate is a blood test that can show if there's inflammation in your body, as well as how severe the inflammation is. Because it's nonspecific, this test is not used as a diagnostic tool by itself, but as part of a diagnostic process to help pinpoint or monitor what's going on in your body. There are few risks associated with this test and there are no contraindications.

After your blood is drawn into a tube, the test measures how fast the erythrocytes (red cells) in your blood settle to the bottom in one hour. Under normal conditions, when there is no inflammatory process or illness, red cells fall slowly. When you have inflammation in your body, increased levels of abnormal proteins in the blood occur, especially proteins called acute phase reactants like fibrinogen and C-reactive protein, causing red cells to stick together and fall more quickly.

Your doctor will likely also order a C-reactive protein (CRP) test along with a sed rate. The CRP test is also a general indicator of inflammation, but changes in inflammatory processes show up more quickly in a CRP test than in a sed rate. These tests are often ordered together to create a more complete picture of inflammation.

Other blood tests that may be ordered at the same time as a sed rate are a complete blood count (CBC) and a comprehensive metabolic panel (CMP). These also help give a general look at what's going on in your body.

Your doctor may order a sed rate for these reasons:

Help Diagnose Inflammatory and Autoimmune Diseases

Symptoms like persistent joint pain or stiffness, headache, weight loss, anemia, pain in your neck or shoulder, or loss of appetite, are associated with rheumatoid arthritis (an autoimmune disease that occurs when your immune system attacks your joints), systemic vasculitis (a condition in which your blood vessels are inflamed), polymyalgia rheumatica (causes muscle pain and stiffness), and temporal (giant cell) arteritis (inflammation in the lining of your arteries).

A sed rate is typically among the first blood tests ordered when one of these diseases is suspected because the results are instrumental in helping to confirm or rule out a diagnosis.

Inflammation is caused by a wide variety of other inflammatory and autoimmune diseases as well, such as inflammatory bowel disease (IBD) and lupus. Your doctor may do a sed rate as part of the diagnostic process, especially if you have vague symptoms and she suspects that you have one of these diseases, or another inflammatory disease.

This test can also help diagnose certain blood disorders.

Unexplained Fever

Your doctor may order a sed rate if you have a fever that doesn't have any obvious causes. The results can help your doctor decide how to further narrow down what may be going on. For instance, if your sed rate is elevated, your doctor can look for an infection or an inflammatory disease. If your results are normal, your doctor knows to look for another cause of your fever.

Monitor Inflammatory Diseases or Cancer

Aside from assisting diagnostic purposes, a sed rate is often ordered periodically to check on inflammatory disease or cancer activity in those who have been diagnosed. As your disease improves with treatment and becomes less active, it's expected that your sed rate would decrease and approach the normal range. If it doesn't, this indicates that your treatment isn't working well or that you're having a flare-up. You will likely have regular sed rates performed to track how well you're responding to treatment.

Before the Test

Your doctor will talk to you about the sed rate test and any others he is running and what he is looking for. Be sure to mention any prescription and over-the-counter medications and supplements you're taking because oral contraceptives, aspirin, cortisone, and vitamin A may affect your test result.

Timing

Blood tests typically take less than five minutes once the technician is ready for you. As long as you're feeling well once your test is completed, you'll be able to leave right away.

Location

Your test may be at your doctor's office or you may be sent to your local hospital or another facility to have it done.

What to Wear

It's helpful to wear a short-sleeved shirt, but you can wear whatever you want. Just be aware that you will need to push or roll your sleeve up if you're wearing long sleeves so the technician can access your vein.

Food and Drink

There are no fasting requirements for a sed rate or a CRP, so if these are the only two tests your doctor wants you to have, you won't need to restrict your diet. If you have a CBC too, you won't need to fast for that either. However, if your doctor wants you to have a CMP test as well, you may need to fast for 10 to 12 hours before the test. Your doctor will give you specific instructions.

Cost and Health Insurance

A sed rate is relatively low-cost and if you have health insurance, it should be covered as any diagnostic test would be. Contact your insurer with any questions.

What to Bring

If you think you'll be waiting to get your test done, you may want to bring along a book or something to do during this time.

During the Test

A lab technician, likely a nurse or phlebotomist, a person who is trained to draw blood, will perform your sed rate test.

Pre-Test

When you check in, you may need to fill out some paperwork, such as a consent form or to give permission to share your test results with other doctors. The person at the front desk will let you know.

Throughout the Test

This test usually only takes a few minutes. Once you've been seated, the technician will find a vein, typically on the inside of your arm, from which to draw your blood. If you have a history of fainting around blood, needles, or medical procedures, let the technician know right away so precautions can be taken.

The technician will tie a piece of rubber around your arm, above the area from which your blood is drawn, to help increase blood flow. If you tend to get queasy, you may want to turn your head or close your eyes at this point. After the area is cleaned with alcohol, a small, thin needle is pushed into your vein. You may feel a little poke, pinch, or a sharp pain, but it should only last a moment.

As your blood is drawn, it's placed in a tall, thin, vertical tube. At this point, you shouldn't feel anything as long as you hold still. Make sure you let the technician know if you start to feel dizzy, lightheaded, or faint.

Once the technician is getting close to being finished, she'll untie the piece of rubber, then take the needle out of your arm, which you probably won't even feel.

Post-Test

If you're bleeding, you may need a tissue or cotton ball pressed over the area for a bit to stop it. If it doesn't stop quickly, you may have a bandage placed over the area to keep the blood contained and to create a little pressure.

As long as you're not feeling faint, dizzy, or nauseous, you can leave as soon as your blood is drawn and the puncture wound has stopped bleeding or has been covered. If you're not feeling well, you may need a little more time to recover before you're able to leave.

After the Test

You can resume your normal activities as soon as you want to. It may take a few days for your test results to come back. Your doctor will let you know when they do.

Managing Side Effects

The risks associated with any blood test are small. You may have bruising, pain, or swelling in the area in which your blood was taken. There's always a minor risk of infection when you have an entrance wound in your skin too.

You can use ice packs on the area and take Advil or Motrin (ibuprofen) to help the pain and swelling if it's bothersome. If these side effects don't go away within a few days or they get worse, call your doctor.

Interpreting Results

The usual method used for sed rate is known as the Westergren method. The results are reported in mm/hr (millimeters per hour). Typically, your sed rate increases with age and it tends to be higher in women. Many laboratories don't adjust for gender or age and, though the high end of this range can vary from lab to lab, they generally consider a normal sed rate as:

  • Men: 0 to 22 mm/hr
  • Women: 0 to 29 mm/hr

When adjusted for age and gender, the typical reference range for the test is:

Adults (Westergren method):

  • Men under 50 years old: Less than 15 mm/hr
  • Men over 50 years old: Less than 20 mm/hr
  • Women under 50 years old: Less than 20 mm/hr
  • Women over 50 years old: Less than 30 mm/hr

Children (Westergren method):

  • Newborn: 0 to 2 mm/hr
  • Newborn to puberty: 3 to 13 mm/hr

Again, this can vary from lab to lab, so talk to your doctor if you have any questions about your results.

A normal sed rate doesn't necessarily mean that you don't have inflammation or disease, but remember, this test helps give an overall idea of what's going on when results are combined with your symptoms and other diagnostic tests. If you're having the test to monitor an already diagnosed inflammatory condition and the results are normal, this means that your treatment is working and/or you weren't having a flare-up at the time of the test.

If your sed rate is abnormal, keep in mind that this test can help diagnose a condition, but your sed rate alone doesn't mean that you necessarily have a medical condition that requires treatment. You will need more tests done to definitively diagnose a specific condition, especially if you have few or no other symptoms of a chronic disease or infection.

An elevated sed rate can occur for a number of reasons. Some of the common inflammatory conditions that are associated with an elevated sed rate include:

  • Severe infections, like a bone infection, skin infection, heart infection, tuberculosis, or rheumatic fever
  • Rheumatoid arthritis
  • Temporal (giant cell) arteritis
  • Systemic vasculitis
  • Polymyalgia rheumatica
  • Inflammatory bowel disease
  • Lupus

Additionally, your sed rate may be moderately higher than normal due to factors such as kidney disease, thyroid disease, certain cancers like multiple myeloma and lymphoma, pregnancy, menstruation, anemia, or aging. Your doctor will take these factors into consideration if any of them apply to you when interpreting your test results.

If you already have a diagnosed inflammatory condition or cancer, your sed rate may be high because your disease is flaring up or not responding well to treatment. This could mean that your treatment plan will need some adjusting.

A lower-than-normal sed rate can occur in these blood disorders:

  • Polycythemia, a high red blood cell count
  • Sickle cell anemia, which involves changes in the shape of some red blood cells
  • Leukocytosis, a high white blood cell count

Follow-Up

In cases where your doctor suspects that you have an inflammatory condition, especially if your symptoms are vague, she may want to repeat your sed rate test. This is just to make sure that there is, indeed, inflammation somewhere in your body before diving into the sometimes long and complicated process of diagnosis.

If you're diagnosed with an inflammatory disease or cancer, your doctor will repeat this test periodically to monitor your treatment progress. In the case of an infection, you may also have this test repeated one or more times to confirm that the infection has gone away.

If your sed rate is elevated and your doctor suspects that you have temporal arteritis, systemic vasculitis, or polymyalgia rheumatica, all types of vasculitis, your sed rate test result will be one of the main supports for your diagnosis, along with the results of other tests and your signs and symptoms. Other tests to help support your diagnosis may include a CBC, CMP, creatinine, liver panel, antineutrophil cytoplasmic antibodies (ANCA) test, complement test, urinalysis, lung function tests, echocardiogram (EKG), and other imaging tests. Treatment for these conditions depends on how severe they are but will likely include medications that suppress the immune system, which is overactive in vasculitis.

Your doctor may order a blood culture if your sed rate is elevated and he suspects that you have a severe infection. This is another blood test that looks for bacteria, fungi, and viruses in your blood. If you have an infection, you may need antibiotics.

When your doctor suspects rheumatoid arthritis (RA) and your sed rate is high, you will likely have a CRP, if you haven't already, along with blood tests that detect rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies. All of these together can help diagnose or rule out RA. Treatment for RA typically includes medications to keep symptoms under control.

If you have symptoms of lupus and your sed rate is elevated, your doctor will need to do more blood tests to look for autoantibodies, such as antinuclear antibody, anti-Smith antibody, anti-double-stranded DNA, anti-SSA, anti-SSB, and anti-RNP. Lupus is a complicated disease that can take a large number of tests to diagnose. Other common tests for lupus include urinalysis, CBC, CMP, cryoglobulin, complement test, serum protein electrophoresis (SPEP), and imaging tests. A variety of medications are used to treat lupus, depending on its severity and symptoms.

If your sed rate was low and you haven't already been diagnosed with a blood disorder like polycythemia, sickle cell anemia, or leukocytosis, your doctor may do additional tests for this. These can include a CBC, CRP, erythropoietin test, vitamin B12 level, arterial blood gases test, blood oxygen saturation, creatinine, potassium, bilirubin, and a sickle cell test. Treatment for these often includes medications, as well as specific options that are targeted toward underlying causes and/or complications of the disease.

Other Considerations

If you have questions about your test results or you're unsure what's going to happen, talk to your doctor. He or she can help you understand your results and the process that may be involved in looking for a specific diagnosis.

You can easily get copies of your medical records by talking to someone in your doctor's office if you decide you'd like a second opinion. Many healthcare systems have your medical records accessible online as well, so ask about that option.

A Word From Verywell

The sed rate may be one of the first of many tests in your diagnostic process, so remember to take it one day at a time. If you're anxious and stressed, try some relaxation techniques such as deep breathing, meditation, yoga, or progressive muscle relaxation. Make sure you're taking time to do things you love and that you have a stress outlet, whether it's an activity, a friend, or a creative pursuit. Soon enough, your doctor will be able to pinpoint what's behind your symptoms and you can start treatment to help improve your quality of life.

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View Article Sources
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