1. On the basis of results from 3000 parallel measurements of serum amyloid A protein (SAA) and C-reactive protein (CRP) in various clinical and experimental conditions, the relationship between these proteins was examined and the question of whether measurements of SAA can provide clinically useful information beyond that from CRP assays was evaluated.
2. The concentrations of SAA and CRP showed a close relationship in a wide range of clinical conditions and the general clinical impact of an elevated SAA or CRP level is similar. SAA was, however, more sensitive than CRP in reflecting inflammatory activity, and in some conditions characterized by normal or only slightly elevated CRP concentrations, measurements of SAA concentrations could be used for monitoring disease activity and response to treatment.
3. Marked variation in the ratios of SAA to CRP concentration occurred in response to different stimuli (e.g. surgical trauma/immunological tissue injury), suggesting the existence of independent, disease-specific pathways of regulation for the serum concentrations of SAA and CRP.