Serum amyloid A protein and C-reactive protein in systemic amyloidosis.

In 106 patients with systemic amyloidosis (56 primary, 27 secondary, and 23 familial), serum amyloid A protein (SAA) was measured by solid-phase radioimmunoassay and C-reactive protein (CRP) was measured by rate nephelometry. SAA and CRP concentrations were highly correlated (r = 0.75, P less than 0.001) throughout the normal and abnormal concentration ranges. In systemic amyloidosis, SAA was more sensitive than CRP as an indicator of the acute-phase response, particularly in secondary amyloidosis. Acute-phase proteins are only occasionally increased during the course of familial amyloidosis. The overlap of acute-phase protein levels does not permit reliable separation of primary amyloidosis from secondary amyloidosis solely on the basis of such studies despite the significantly higher SAA and CRP levels in the latter.