Doctors call the ESR test a nonspecific test, as it only confirms the presence or absence of inflammatory activity in the body. Doctors typically use other lab tests, clinical findings, and the person’s health history alongside ESR test results to make a diagnosis.
Inflammation usually occurs in the body as a result of underlying medical conditions, such as infection, cancer, or an autoimmune disease.
Doctors also use the ESR test to monitor how conditions, such as those below, are progressing or responding to treatment.
- rheumatoid arthritis, an autoimmune condition that causes inflammation in the joints
- temporal arteritis, a type of blood vessel inflammation
- polymyalgia rheumatica, a complication of temporal arteritis
- systemic vasculitis, inflammation of the lining of the blood vessels
In this article, we look at the ESR test procedure and what the results might indicate. We also explain the possible risks of the procedure.
The ESR test measures the rate at which the red blood cells, or erythrocytes, in a sample of blood settle at the bottom. This process of settling is called sedimentation.
A doctor will draw a small amount of blood from the individual’s vein and send it to a laboratory. There, lab technicians will transfer the blood to a vertical test tube in which the red blood cells will slowly settle at the bottom. This will leave a clear, yellowish fluid at the top, which is blood plasma.
The result of the test will depend on the amount of plasma at the top of the tube after 1 hour. The measurement will be in millimeters per hour (mm/hr).
Red blood cells settle at a faster rate in people with inflammatory conditions. These conditions trigger an inflammatory process in the body, which leads to an increase in the number of proteins in the blood. This increase causes red blood cells to clump together and settle more quickly.
People whose red blood cells settle faster will have elevated ESR values, indicating to doctors that a medical condition may be present.
The result of the ESR test is the amount of plasma remaining at the top of the test tube after 1 hour.
The test is not specific to a particular condition, which means that doctors have to use the results alongside other clinical information to make an accurate diagnosis and determine whether or not the individual has a disease.
The normal reference range for ESR results is 1–13 mm/hr for males and 1–20 mm/hr for females. These values can also vary depending on the person’s age. People with ESR results outside the standard range may have a medical condition.
People with low ESR values may have:
- sickle cell anemia, a condition that affects the shape of red blood cells
- leukemia, a blood cell cancer
- a high red blood cell count
- congestive heart failure
- low levels of the protein fibrinogen in the blood
- hyperviscosity, an increase in blood thickness
- a very high white blood cell count