ESR is an acute phase reactant which indicates the presence and intensity of an inflammatory process. An erythrocyte sedimentation rate (ESR) is a type of blood test that measures how quickly erythrocytes (red blood cells) settle at the bottom of a test tube that contains a blood sample. A high value of ESR can be seen in the following conditions: infection, rheumatoid arthritis, rheumatic fever, vascular disease, inflammatory bowel disease, heart disease, kidney disease, certain cancers, and other chronic inflammatory conditions.