The ESR rate is only one of many markers to determine inflammation. Determination of inflammation is only one of many indicators of auto-immune disorders. Therefore, the rate (or reliability of the rate) alone will not determine if a particular disease is present or not. ESR is said to be nonspecific because increases do not tell the doctor exactly where the inflammation is in your body or what is causing it, and also because the rate can be affected by other conditions besides inflammation. For this reason, ESR is typically used in conjunction with other tests.
Again, since ESR is a nonspecific marker of inflammation and is affected by other factors, the results MUST be used along with the doctor's other clinical findings, with your health history, and with results from other appropriate laboratory tests. If the ESR and other clinical findings match a specific disorder, the doctor may be able to confirm or rule out a suspected diagnosis.
Doctor's do not base their decisions solely on the ESR results. You can have a normal result and still have a problem. Moderately elevated ESR occurs with inflammation, but it also occurs with anemia, infection, pregnancy, and old age.
A very high ESR usually has an obvious cause, such as a marked increase in globulins that can be due to a severe infection. So, your doctor will use other follow-up tests, such as cultures, depending on the your symptoms. Persons with multiple myeloma or Waldenstrom's macroglobulinemia (tumors that make large amounts of immunoglobulins) typically have very high ESRs even if they don't have inflammation. As noted before, polymyalgia rheumatica and temporal arteritis may also have very high ESRs and some auto-immune disorders (such as Lupus) can sometimes have very high ESRs. Usually, doctors will run ESR and C-reactive protein (CRP) tests because they are both markers of inflammation.
A rising ESR can mean an increase in inflammation or a poor response to a particular drug therapy; a decreasing ESR can mean a good response.
I hope that this has been helpful to you.
Peace and Blessings
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