Monitoring both serum amyloid protein A and C-reactive protein as inflammatory markers in infectious diseases.

We examined serum amyloid protein A (SAA) and C-reactive protein (CRP) as inflammatory markers of viral and bacterial infections. Both acute-phase reactants increased in the acute stage and thereafter decreased in the convalescent stage. In viral infections, the mean serum concentrations of SAA during the acute stage were 141 mg/L in infections with adenovirus, 77 mg/L with measles virus, 63 mg/L with influenza virus, 55 mg/L with parainfluenza virus, 31 mg/L with respiratory syncytial virus, and 31 mg/L in aseptic meningitis. The mean serum concentration of CRP was 19 mg/L for adenovirus infection and < 7 mg/L in all other viral infections. The SAA concentrations were 5- to 11-fold greater than the CRP concentrations. Both the SAA and the CRP concentrations were higher in bacterial infections than in viral infections. Changes in the concentrations of serum SAA paralleled those in serum CRP in bacterial infection; during the course of viral infection, however, serum SAA tended to disappear more quickly than CRP did. SAA appears to be a clinically useful marker of inflammation in acute viral infections, with or without significant changes in the CRP concentration.