Correlations between serum amyloid A protein and C-reactive protein in infectious diseases.

Serum amyloid A (SAA) protein is an acute phase reactant that has recently become of increasing interest as a marker for disease and treatment monitoring. We have correlated SAA levels to those of C-reactive protein (CRP) in sera from 98 patients admitted to an infectious diseases clinic because of viral and bacterial infections, including hepatitis A and B, cytomegalovirus infection, varicellae-zoster, infectious mononucleosis, influenza A, bacterial pneumonia, streptococcal pharyngitis, bacterial sepsis and severe bacterial sepsis. The study population was chosen from the clinical setting as representatives of these frequently encountered patient groups. SAA levels correlated significantly with CRP levels (r2=0.757, p<0.001) for the entire studied population. Furthermore, positive correlations were found in viral (r2=0.572, p<0.001) and bacterial (r2=0.666, p<0.001) infections. Positive correlations were also observed when the values were compared in accordance with CRP levels higher and lower than 100 mg/L (r2=0.689, p<0.001; CRP>100; r2=0.397, p<0.001; CRP<100). Because SAA is more sensitive than CRP for the detection of minor inflammatory stimuli, as in the viral and low CRP groups, we conclude that SAA can be of use in several viral infections, as well as in non-invasive and early invasive bacterial infections.