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ESR

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Also known as: Sed Rate; Sedimentation Rate; Westergren Sedimentation Rate
Formal name: Erythrocyte Sedimentation Rate

The Test Sample

What is being tested?

Erythrocyte sedimentation rate (ESR or sed rate) is a test that indirectly measures the degree of inflammation present in the body. The test actually measures the rate of fall (sedimentation) of erythrocytes (red blood cells) in a sample of blood that has been placed into a tall, thin, vertical tube. Results are reported as the millimeters of clear fluid (plasma) that are present at the top portion of the tube after one hour.

When a sample of blood is placed in a tube, the red blood cells normally settle out relatively slowly, leaving little clear plasma. The red cells settle at a faster rate in the presence of an increased level of proteins, particularly proteins called acute phase reactants. The level of acute phase reactants such as C-reactive protein (CRP) and fibrinogen increases in the blood in response to inflammation.

Inflammation is part of the body's immune response. It can be acute, developing rapidly after trauma, injury or infection, for example, or can occur over an extended time (chronic) with conditions such as autoimmune diseases or cancer.

The ESR is not diagnostic; it is a non-specific test that may be elevated in a number of these different conditions. It provides general information about the presence or absence of an inflammatory condition.

There have been questions about the usefulness of the ESR in light of newer tests that have come into use that are more specific. However, ESR test is typically indicated for the diagnosis and monitoring of temporal arteritis, systemic vasculitis and polymyalgia rheumatica. Extremely elevated ESR is useful in developing a rheumatic disease differential diagnosis. In addition, ESR may still be a good option in some situations, when, for example, the newer tests are not available in areas with limited resources or when monitoring the course of a disease.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.