Understanding the Erythrocyte Sedimentation Rate (ESR)

The erythrocyte sedimentation rate, commonly called ESR, is a simple blood test that measures how quickly red blood cells settle to the bottom of a test tube over a specified period—usually one hour. The result is expressed in millimeters per hour (mm/hr). ESR is a non‑specific marker of inflammation and is often ordered as part of a routine blood panel or to help diagnose or monitor certain medical conditions.

What Is ESR?

When a blood sample is placed in a vertical tube, red blood cells (erythrocytes) naturally fall under gravity. In the presence of inflammatory proteins, such as fibrinogen and immunoglobulins, the cells tend to clump together and settle faster. The ESR test quantifies this rate, providing a quick snapshot of the body’s inflammatory status.

How ESR Is Measured

After the sample is collected, it is placed in a standardized tube and allowed to stand upright for exactly one hour. The laboratory measures the distance the red cells have descended and reports the value in mm/hr. A result of 26 mm/hr, for example, indicates that the cells have settled 26 millimeters in that hour.

Interpreting an ESR of 26 mm/hr

Normal Ranges by Age and Sex

Normal ESR values vary by age, sex, and laboratory method. Typical reference ranges are: