Serum amyloid A: A biomarker to aid in assessing cats with acute pyelonephritis and monitoring response to antibiotic therapy.

ObjectivesSerum amyloid A (SAA), the major acute-phase protein in cats, has potential, as in humans, to aid in the diagnosis and treatment of bacterial infections. This study compared SAA concentrations in cats with acute pyelonephritis (APN) with stable chronic kidney disease (CKD) and healthy cats. In cats with APN, SAA concentrations were monitored during antibiotic treatment to assess whether they correlated with clinical scores.MethodsA multicenter study recruited client-owned cats with APN (n = 9), with stable CKD (n = 10) or healthy cats (n = 10). Cats with APN were monitored for 21 days during antibiotic therapy to assess SAA concentrations along with clinical scores.ResultsThe majority of cats with APN were older (>10 years) and spayed females (8/10), with 5/9 having pre-existing CKD. Median SAA concentrations were significantly higher in cats with APN (235.3 mg/l, range 9.1-810) than in healthy cats (1.85 mg/l, range 1-2.7; P = 0.0008) and cats with stable CKD (1.45 mg/l, range 0.1-8.9; P = 0.0002). Cats with APN reached peak SAA concentrations (412 mg/l, range 18.6-810) within 48 h of presentation. In addition, with treatment and clinical recovery, median SAA concentrations returned to normal (3.1 mg/l, range 1-7.2) within 14 days. SAA concentrations were moderately correlated with clinical scores (rs = 0.650).Conclusions and relevanceThe results of this study offer additional insights into the potential benefits and limitations of monitoring SAA concentrations in cats with APN. Cats with APN experience increased SAA concentrations, supporting SAA as a diagnostic tool for identifying affected cats. Serial SAA monitoring may help assess clinical recovery or determine treatment failure.