Erythrocyte Sedimentation Rate (ESR) is a simple non-specific blood test that indicates inflammation. A sample of blood is collected and placed in a graduated container. After one hour, the separation of blood cells from plasma is measured, and reported in mm/hour.

The sedimentation rate is affected by the amount of fibrinogen in blood. Elevated levels of fibrinogen cause red blood cells to adhere to each other, and thus increase the rate at which they sink.

ESR is used to evaluate the presence of inflammatory states, but does not reveal the cause.