What is the ESR test? The ESR is a simple blood test that measures how quickly red blood cells (erythrocytes) settle at the bottom of a test tube. When there's inflammation in the body, certain proteins in the blood cause red blood cells to clump together and settle faster. Therefore, a higher ESR can indicate inflammation.   What the ESR test is used for: The ESR is a non-specific test, meaning it can detect inflammation but doesn't pinpoint the cause. It's often used to:   Help diagnose conditions associated with inflammation: Such as infections, autoimmune diseases (like rheumatoid arthritis or lupus), and some cancers. Monitor the activity of inflammatory diseases: To see if treatment is working.   Important Note: A high ESR doesn't always mean there's a serious problem. It can be elevated due to various factors, including:   Infections Autoimmune diseases   Pregnancy Older age