Serum Amyloid A Protein (SAA) in Healthy and Infected Individuals

Sammanfattning: Serum amyloid A protein (SAA) is an acute phase protein that has recently gained increasing interest as a potential marker for disease and treatment monitoring. We investigated SAA and CRP levels in (a) patients with various common infectious diseases (n=98), (b) patients with pyelonephritis (n=37) versus patients with cystitis (n=32), (c) healthy individuals of varying ages (n=231), (d) very immature newborn infants with or without nosocomial infections (NIs) (n=72) and (e) patients with bacterial infections treated with cefuroxime (n=81). SAA significantly correlated with CRP in viral as well as in bacterial infections (for the total group: r2=0.757, p<0.0001) and showed a systemic inflammatory response in 90% of the patients with cystitis as compared with 23% for CRP. Equally high efficiencies (0.96 and 0.94 for SAA and CRP, respectively) were observed in discriminating between pyelonephritis and cystitis. SAA and high sensitive (hs) CRP were lower in umbilical cords (p<0.0001) and higher in elderly adults (p<0.0001-0.03) than in the other age groups; higher in immature newborn infants than in term infants; and higher in the NI group than in the non-NI group. Interindividual variabilities of the time course of the biomarkers SAA and CRP were considerable. Because of the smoothed distribution of SAA and CRP (i.e. elevations were both essentially unchanged during the first 3 days of cefuroxime treatment), these markers were not useful when deciding parenteral-oral switch of therapy, which occurred within this time period in most cases.SAA is a sensitive systemic marker in cystitis. SAA and hsCRP in umbilical cord blood are close to the detection limit and increase with age. They increase in relation to NI in very immature newborn infants and might therefore be used in diagnosis and monitoring. Finally, SAA and CRP in adults with bacterial infections could not predict an early parenteral-oral switch of antimicrobial therapy.