The erythrocyte sedimentation rate (ESR or sed rate) is a relatively simple, inexpensive, non-specific test that has been used for many years to help detect inflammation associated with conditions such as infections, cancers, and autoimmune diseases.

ESR is said to be a non-specific test because an elevated result often indicates the presence of inflammation but does not tell the health practitioner exactly where the inflammation is in the body or what is causing it. An ESR can be affected by other conditions besides inflammation. For this reason, the ESR is typically used in conjunction with other tests, such as C-reactive protein.

ESR is used to help diagnose certain specific inflammatory diseases, temporal arteritis, systemic vasculitis and polymyalgia rheumatica. A significantly elevated ESR is one of the main test results used to support the diagnosis.

This test may also be used to monitor disease activity and response to therapy in both of the above diseases as well as some others, such as systemic lupus erythematosus (SLE).

An ESR may be ordered when a condition or disease is suspected of causing inflammation somewhere in the body. There are numerous inflammatory conditions that may be detected using this test. For example, it may be ordered when arthritis is suspected of causing inflammation and pain in the joints or when digestive symptoms are suspected to be caused by inflammatory bowel disease.

A health practitioner may order an ESR when an individual has symptoms that suggest polymyalgia rheumatica, systemic vasculitis, or temporal arteritis, such as headaches, neck or shoulder pain, pelvic pain, anemia, poor appetite, unexplained weight loss, and joint stiffness. The ESR may also be ordered at regular intervals to assist in monitoring the course of these diseases.

Before doing an extensive workup looking for disease, a health practitioner may want to repeat the ESR.

The result of an ESR is reported as the millimeters of clear fluid (plasma) that are present at the top portion of the tube after one hour (mm/hr).

Since ESR is a non-specific marker of inflammation and is affected by other factors, the results must be used along with other clinical findings, the individual's health history, and results from other laboratory tests. If the ESR and clinical findings match, the health practitioner may be able to confirm or rule out a suspected diagnosis.

A single elevated ESR, without any symptoms of a specific disease, will usually not give enough information to make a medical decision. Furthermore, a normal result does not rule out inflammation or disease.

Moderately elevated ESR occurs with inflammation but also with anemia, infection, pregnancy, and with aging.

A very high ESR usually has an obvious cause, such as a severe infection, marked by an increase in globulins, polymyalgia rheumatica or temporal arteritis. A health practitioner will typically use other follow-up tests, such as blood cultures, depending on the person's symptoms. People with multiple myeloma or Waldenstrom's macroglobulinemia (tumors that make large amounts of immunoglobulins) typically have very high ESRs even if they don't have inflammation.

When monitoring a condition over time, rising ESRs may indicate increasing inflammation or a poor response to a therapy; normal or decreasing ESRs may indicate an appropriate response to treatment.

A low ESR can be seen with conditions that inhibit the normal sedimentation of red blood cells, such as a high red blood cell count (polycythemia), significantly high white blood cell count (leukocytosis), and some protein abnormalities. Some changes in red cell shape (such as sickle cells in sickle cell anemia) also lower the ESR.

ESR and C-reactive protein (CRP) are both markers of inflammation. Generally, ESR does not change as rapidly as does CRP, either at the start of inflammation or as it resolves. CRP is not affected by as many other factors as is ESR, making it a better marker of inflammation. However, because ESR is an easily performed test, many health practitioners still use ESR as an initial test when they think a patient has inflammation.

If the ESR is elevated, it is typically a result of two types of proteins, globulins or fibrinogen. Depending on the tested person's medical history, signs, symptoms and what the health practitioner suspects is the cause, he or she may then order a fibrinogen level (a clotting protein that is another marker of inflammation) and a serum protein electrophoresis to determine which of these (or both) is causing the elevated ESR.

Women tend to have a higher ESR, and menstruation and pregnancy can cause temporary elevations.

In a pediatric setting, the ESR test is used for the diagnosis and monitoring of children with rheumatoid arthritis or Kawasaki disease.

Drugs such as dextran, methyldopa, oral contraceptives, penicillamine procainamide, theophylline, and vitamin A can increase ESR, while aspirin, cortisone, and quinine may decrease it.

There is a commercial rapid test available that performs the ESR in 4 minutes by a centrifugal method. It is being used more widely to shorten waiting times for patients, particularly in emergency departments.