Erythrocyte Sedimentation Rate (Sed Rate) Overview

An erythrocyte sedimentation rate, commonly referred to as a sed rate, is a blood test that is used to diagnose nonspecific inflammation in the body. An elevated (abnormally high) sed rate suggests that there is an ongoing inflammatory process, but this test doesn't identify where it is in the body or why it's occurring. Your healthcare provider may order this test during an evaluation for possible rheumatoid arthritis or lupus, to monitor diseases such as cancer, or for other reasons.

Purpose of Test

Inflammation is the immune system's response to 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 result can be an indication of the severity of inflammation. Because it's nonspecific, this test is not used as a diagnostic tool by itself, but as part of a diagnostic process along with other tests.

There are few risks associated with this test and there are no contraindications.

After blood is drawn into a tube, the test measures how fast the erythrocytes (red blood cells) in the blood settle to the bottom in one hour. Under normal conditions, when there is no inflammatory process or illness, red cells fall slowly. With inflammation, certain proteins in the blood, like fibrinogen, cause red cells to stick together and fall more quickly. These proteins are called acute phase reactants.

A C-reactive protein (CRP) test is often ordered along with a sed rate. A high CRP is a general indicator of inflammation, and changes in inflammatory processes show up more quickly in a CRP test than in a sed rate.

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).

Inflammatory and Autoimmune Diseases

If you have certain symptoms, your healthcare provider may order a sed rate as part of the diagnostic process.

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

Inflammation, possibly with a high sed rate, is also caused by a wide variety of inflammatory and autoimmune diseases, such as inflammatory bowel disease (IBD) and lupus.

This test can also help diagnose certain blood disorders.

Unexplained Fever

Your healthcare provider may order a sed rate if you have a fever that doesn't have any obvious causes.

Along with your other test results, your sed rate can help point to whether you have inflammation.

Monitor Inflammatory Diseases or Cancer

A sed rate is often ordered periodically to help assess the progression or treatment response of inflammatory disease or cancer.

As some conditions improve with treatment, it's expected that the sed rate would decrease and approach the normal range.

Before the Test

If you need to have this test, your healthcare provider will talk to you about why you are having it and what they are looking for.

Be sure to tell your provider about all prescription and over-the-counter medications and supplements you're taking. 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 after the blood draw, you'll be able to leave right away.

Location

Your test may be at your healthcare provider's office or you may get it at a local hospital or another facility.

What to Wear

You can wear whatever you want, but it's helpful to wear a short-sleeved shirt. 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, CRP, or CBC, so if these are the only tests you are having, you won't need to restrict your diet.

If you are having a CMP test as well, you may need to fast for 10 to 12 hours before the test. Your healthcare provider will give you specific instructions.

Cost and Health Insurance

If you have health insurance, a sed rate test 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 technician, nurse or phlebotomist 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 healthcare providers. 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 or needles, let the technician know 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 pressure in the veins. After the area is cleaned with alcohol, a small, thin needle is pushed into your vein. You may feel a little poke, pinch, or 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.

Once the technician is getting close to being finished, they'll untie the piece of rubber, then take the needle out of your arm.

Post-Test

If you're bleeding, you may need a tissue or cotton ball pressed over the area for a bit to stop it. You will then have a bandage placed over the area to prevent contamination of the tiny skin puncture.

As long as you're not feeling faint, dizzy, or nauseous, you can leave as soon as the puncture wound has stopped bleeding and 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.

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. You can use ice packs on the area and take Advil or Motrin (ibuprofen) to help with pain or swelling.

There's a minor risk of infection at the puncture site—keeping it clean and covering it with a bandage is typically enough to prevent an infection.

If the area feels warm, develops pus, or pain or swelling worsens or persists, call your healthcare provider.

Interpreting Results

The Westergren method is the usual technique used for measuring sed rate. The results are reported in mm/hr (millimeters per hour). Typically, sed rate increases with age and it tends to be higher in women. Some laboratories adjust for gender or age, while some labs don't. The standard range can vary slightly between labs.

Standard normal sed rate:

• 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

A normal sed rate doesn't necessarily mean that you don't have inflammation or disease. This test helps give an overall idea of what's going on when results are considered along with symptoms and other diagnostic tests. If you're having the test to monitor an already diagnosed inflammatory condition and the results are normal, this could suggest 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.

An elevated sed rate can occur for a number of reasons. Some of the conditions that are commonly 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
• Most types of 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 healthcare provider 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 at times when your disease is flaring up or not responding well to treatment.

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

The follow-up testing after a sed rate test is often guided by symptoms, medical history, and physical examination, which determine the most likely cause of inflammation.

If your sed rate is elevated and your healthcare provider suspects that you have temporal arteritis or polymyalgia rheumatica, 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, electrolyte levels, creatinine, liver panel, antineutrophil cytoplasmic antibodies (ANCA) test, complement levels, urinalysis, lung function tests, echocardiogram, 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 healthcare provider may order a blood culture if your sed rate is elevated and there's a concern that you might have a severe infection. This is a blood test that looks for bacterial or fungal growth in your blood.

When your healthcare provider 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, in addition to your sed rate, your healthcare provider 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, complement levels, and imaging tests. A variety of medications are used to treat lupus, depending on its severity and symptoms.

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 healthcare provider will be able to pinpoint what's behind your symptoms and you can start treatment to help improve your quality of life.