Erythrocyte Sedimentation Rate, or ESR, is a blood test used to measure the rate at which red blood cells settle in a tube over a certain period of time. It is a non-specific marker of inflammation and can help diagnose or monitor various medical conditions.

ESR is used to detect and monitor inflammatory or infectious conditions, such as infections, autoimmune diseases, and certain cancers. It can provide valuable information to healthcare professionals when diagnosing and managing these conditions.

The Westergren Method is one of the standard techniques for measuring ESR. In this method, blood is mixed with an anticoagulant and placed in a tall, thin tube, and the rate at which red blood cells settle to the bottom of the tube over the course of one hour is recorded.

ESR is typically reported in milli meters per hour (mm/hr), which represents how far the red blood cells have settled in the tube in one hour.

The reference ranges can vary depending on the laboratory and the patient's age and gender. Generally, a normal ESR for adults is around 0-20 mm/hr for men and 0-30 mm/hr for women. However, these values can be affected by various factors and should be interpreted by a healthcare professional in the context of the patient's medical history.