The Erythrocyte Sedimentation Rate (ESR) is the rate at which the erythrocytes settle down. Normally, the red blood cells (RBCs) remain suspended uniformly in circulation. This is called suspension stability of RBCs. If blood is mixed with an anticoagulant and allowed to stand on a vertical tube, the red cells settle down due to gravity with a clear layer of plasma laying on top of the red cells (=supernatant layer). The ESR test measures how long it takes for red blood cells to fall to the bottom of the test tube vertically for one hour. The quicker they fall, the more likely it is that there are increased levels of inflammation.
ESR is influenced by two main factors:
- Properties of the RBC – changes in size, shape and number of RBCs due to certain diseases will affect the ESR.
- Properties of the plasma – the amount and type of plasma protein present in a blood sample may affect the ESR.
If protein levels are used, the ESR may be increased. ESR is not a specific test for any particular disease. An ESR is often used to aid diagnosis in conditions associated with inflammation, such as:
- Crohn’s disease
- Temporal arteritis
- Polymyalgia rheumatica
Along with other tests, an ESR can be useful in confirming whether you have an infection in the body. It is not uncommon for pregnant women to have elevated ESR readings.
ESR is measured in millimeters per hour (mm/h). The normal values are:
0 to 10 mm/h in children
0 to 15 mm/h in men younger than 50
0 to 20 mm/h in men older than 50
0 to 20 mm/h in women younger than 50
0 to 30 mm/h in women older than 50