Utility of inflammatory markers for rheumatological diseases

Evidence of active inflammation is supportive in diagnosing inflammatory rheumatological diseases but is not diagnostic. Elevation of the acute phase reactants, serum C-reactive protein (CRP) concentration and erythrocyte sedimentation rate (ESR) are nonspecific, surrogate markers of inflammation. Compared to ESR, serum CRP concentration changes more quickly and is not affected by age or hyperviscosity (eg hypergammaglobulinaemia). Consider infection in people with an elevated serum CRP concentration and a normal ESR, particularly in people with established inflammatory connective tissue disease. A normal ESR or serum CRP concentration does not exclude an inflammatory pathology.

Other indirect indicators of systemic inflammation include:

• mild normochromic, normocytic anaemia, with raised serum ferritin and low serum iron concentrations, suggests anaemia of chronic disease associated with systemic inflammation
• thrombocytosis
• hypergammaglobulinaemia.

An elevated white cell count suggests infection rather than inflammation.