Amyloid-related serum protein (SAA) as an indicator of lung infection in cystic fibrosis.

Amyloid-related serum protein (SAA) was analysed by radioimmunoassay in 32 patients with cystic fibrosis, and compared with other acute phase reactants and lung function. The level of SAA showed significant correlation with impaired lung function due to active Pseudomonas aeruginosa infection, and also to C-reactive protein. SAA seemed to correlate better to the presence of bacteria in sputum than C-reactive protein. Ten of the patients received extensive antibiotic treatment for their pulmonary infection, and falling serum levels of SAA paralleled the clinical response to treatment. Thus the concentration of SAA in these patients was a valuable guide for the selection of patients for antibiotic treatment as well as a good parameter of the response to therapy.