The ESR is the time-honoured test used to measure the acute phase response to "screen" for the presence of infection or inflammation and to monitor "disease activity". Measurement of plasma viscosity (PV) and specific proteins such as CRP are more recent innovations.
For general screening purposes and monitoring of inflammatory disorders the PV, ESR and CRP is convenient and readily available in the laboratory. It should be interpreted together with the full blood count, eg evidence of "secondary anaemia" or other indicators of inflammation, to give a more complete picture. PV and CRP have been largely used for the rheumatic and connective tissue disorders including cranial arteritis, and inflammatory bowel disease.
||Test reflects the presence of:
||Effect of anaemia
||Advantages and Disadvantages
||fibrinogen, immunoglobulins and abnormal proteins
||rise in ESR
||no technique for calibration to test for accuracy; poor reproducibility; affected by anaemia.
||macro-molecules e.g. fibrinogen and globulins
||automatable; measurement can be made on stored blood samples (non refrigerated)
||precise measurements of C-Reactive Protein
||automatable; very sensitive early but short lived indicator
Which acute phase test should be used in practise?
Cranial arteritis is a condition in which the ESR and PV have been particularly used to confirm clinical suspicion and initiate urgent steroid therapy. Comparative studies have failed to show an advantage to either technique and a normal result should never dissuade the clinician from starting steroids if the clinical picture is highly suggestive.
A raised CRP is particularly useful for the identification of patients with occult bacterial infection eg endocarditis. CRP has been well evaluated for this purpose and is readily available. It may be useful to perform this test sequentially eg daily, in this context.
||Age and Sex
||men <50 yrs, women < 50 yrs, both sexes> 50 yrs
||05 mm/h, 0-7 mm/h, <30 mm/h
||2 mL EDTA
||independent of age and sex
||2 mL EDTA
||variable but constant within individuals
||2 mL serum tube