ESR provides a non-specific screening test for the presence of an acute phase reaction.
CRP measures one specific acute phase reactant.
Although the ESR and CRP may be valuable indicators of an acute phase response, normal results do not exclude active disease. There is little added diagnostic value in measuring other specific proteins. However, an awareness that they are acute phase reactants is of value in the interpretation of results in patients with inflammatory or neoplastic disorders.
Levels of Fibrinogen, Ferritin, Haptoglobin, Alpha-1-antitrypsin, Caeruloplasmin, Factor VIII, von Willebrand factor, Complement CH50 or CH100 and Complement components C3 and C4 may be increased in an acute phase response and mask a true deficiency state, if present.
Levels of some proteins may be reduced during an acute phase response, eg, Albumin, Prealbumin (transthyretin), Transferrin. Although an acute phase response can be detected by Protein electrophoresis (serum), this is not an appropriate test in this situation.
Cryofibrinogen may also be present in patients with an acute phase reaction, but this finding has no diagnostic value.
See also Erythrocyte sedimentation rate, and C-Reactive protein.