ESR is generally used as a marker of acute phase reaction and inflammation, although there are now better, more specific markers of acute phase reactions including:
higher concentrations of fibrinogen and alpha-globulins
higher plasma albumin concentration
size, shape and number of RBCs (eg. anaemia may cause raised ESR)
renal failure
obesity
old age
female gender
malignancy
non-acute phase reaction proteins such as immunoglobulins
these proteins all have half-lives of days to weeks, and there is a significant lag time between changes at the clinical level and variations in the ESR.
these non-acute phase influences, plus the influence of various other factors on the ESR such as diurnal variation, and food intake, makes it an imprecise guide to disease activity in most cases
furthermore, the ESR response to acute phase reaction is slow resulting in early false negative results, and may take weeks or months to resolve
however, ESR remains helpful in certain clinical situations such as:
the detection of heavy chain multiple myeloma although plasma and urine protein electrophoresis are far more specific tests
as an acute inflammatory marker, and marker for most auto-immune conditions (including polymyalgia rheumatica, temporal arteritis, subacute thyroiditis), C reactive protein (CRP) is generally a better test.