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Overview

What Is an ESR Blood Test?

An ESR blood test, also called an erythrocyte sedimentation rate or sed rate blood test, measures how quickly red blood cells settle to the bottom of a tube of blood. Faster settling can provide a general, nonspecific signal that inflammation may be present in the body.

ESR cannot identify the specific disease or cause of inflammation. A clinician interprets this sedimentation rate blood test alongside your symptoms, medical history, examination findings, and other test results.

When It Is Needed

Why Is an ESR Blood Test Ordered?

A clinician may order an ESR test when your symptoms suggest inflammation or when an inflammatory, infectious, autoimmune, or another underlying condition is being considered. It may also help monitor a known inflammatory condition over time, but it does not provide a diagnosis by itself.

  • Unexplained fever
  • Joint or muscle pain
  • Prolonged or unexplained fatigue
  • Symptoms that may suggest an autoimmune or inflammatory condition
  • Monitoring a known inflammatory condition

Preparation

How to Prepare for an ESR Blood Test

An ESR blood analysis typically does not require fasting or special preparation. However, follow the laboratory’s instructions, especially if other blood tests are being collected during the same visit.

  • Drink fluids unless your clinician or laboratory tells you otherwise
  • Wear clothing that allows easy access to your arm
  • Tell the clinician about medicines and supplements you take
  • Mention pregnancy or medical conditions that could affect results
  • Ask whether preparation for any additional blood tests is different

During the Test

What Happens During the ESR Test?

The ESR is a single-session venous blood draw. A clinician cleans the skin, inserts a needle into a vein, collects blood into a tube, removes the needle, and applies pressure and a bandage to the puncture site.

In the laboratory, the sample is placed in a tube and the distance that red blood cells settle during a specified period is measured. The lab reports this as a sedimentation rate; the laboratory process itself does not establish a diagnosis.

Risks

What Are the Risks of an ESR Blood Test?

  • Brief pain or stinging when the needle is inserted
  • A small amount of bleeding
  • Bruising near the puncture site
  • Mild soreness in the arm

Uncommon risks include infection, prolonged bleeding, or feeling faint. Seek clinical advice if symptoms are severe, persistent, worsening, or otherwise concerning after the blood draw.

Results

Understanding ESR Blood Test Results

An ESR blood report usually gives a numeric sedimentation rate, commonly in millimeters per hour (mm/hour). The reference range can vary by laboratory, age, sex, and testing method, such as the Westergren method, so use the range printed on your report rather than a general online range.

Factors That Can Affect an ESR Result

A high ESR may occur with inflammation or infection, but it can also be affected by anemia, pregnancy, age, kidney disease, medicines, or other conditions. A low result can also have several explanations and does not automatically rule out disease; an elevated ESR or low ESR must be considered in context.

Interpreting results

An ESR result is not a diagnosis

Do not interpret an ESR result alone or use it to self-diagnose. Discuss an elevated, unexpectedly low, or symptom-inconsistent result with the ordering clinician, who may compare it with CRP, blood counts, symptoms, and other tests.

Diseases & Conditions

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