The erythrocyte sedimentation rate (ESR) test and the C-reactive protein (CRP) test are laboratory blood tests that healthcare professionals use to detect and monitor inflammation in the body. Both ESR and CRP are increased in the presence of acute inflammatory conditions, such as rheumatoid arthritis, polymyalgia rheumatica, inflammatory bowel disease, and other autoimmune conditions. The ESR measures the rate at which red blood cells separate from the fluid component of blood, the serum, with an increased rate of separation indicative of increased blood protein levels of fibrinogen, immunoglobulins, and other chemical agents that are present in inflammatory states. On the other hand, CRP measures the level of C-reactive protein, a substance that is generated by the liver in infectious or inflammatory situations. As a result, while both may indicate inflammation, ESR is an indirect sign of the condition and CRP is a direct indicator of it.
These tests are also useful to monitor the activity of autoimmune diseases and the patient's response to any medications that physicians prescribe to treat the condition. Changes in ESR are slower than changes in CRP, so it is a less sensitive indicator. In addition, many non-inflammatory conditions may elevate the ESR, such as anemia, menstruation, pregnancy, and use of a variety of medications. While both tests are readily available commercially, the ESR test is easier and less expensive than CRP.
Healthcare professionals obtain both ESR and CRP levels by drawing blood from a peripheral vein. When heart disease is suspected in an apparently healthy person, a medical professional may order high-sensitivity C-reactive protein (hs-CRP) test to evaluate the potential risk for cardiac injury. The hs-CRP detects extremely small quantities of C-reactive protein in the blood stream in the range of 0.5 to 10 milligrams per liter of blood (0.00007 ounce per gallon), providing the high degree of sensitivity required to identify accurately an initial or proceeding heart attack. Neither ESR nor CRP tests are sensitive enough for cardiovascular disease applications.
Recent studies indicate that ESR tests may play a beneficial role in screening elderly patients for occult disease. A radical increase of the ESR strongly suggests a problem, most often an autoimmune disease, infection, or even a spreading cancer. Many patients with an ESR level exceeding 100 have myeloma, a condition in which certain white blood cells proliferate excessively and destroy body organs. As a result, a high level in an elderly patient may require further testing, such as additional blood and urine tests, chest X-rays, and liver function tests.