Retrospective evaluation of C-reactive protein for discriminating between lower urinary tract infections and acute pyelonephritis in dogs

Background: The role of C-reactive protein (CRP) in differentiating pyelonephritis from other types of urinary tract infection in dogs is not well defined. Hypothesis/objectives: Compare serum CRP concentrations at diagnosis in dogs with acute pyelonephritis (APy), acute prostatitis (APr), and bacterial cystitis (BC). Serum CRP concentration is hypothesized to be higher in APy and APr than in BC. Animals: One hundred fifteen client-owned dogs were included: 56 with BC, 32 with APy, 23 with APr, and 4 with both APy and APr. Methods: Retrospective observational study. Dogs with positive urine culture were included and divided into 3 groups (BC, APy, and APr), based on medical history. Dogs with comorbidities potentially affecting CRP concentrations and dogs with subclinical bacteriuria were excluded. Data were compared among groups, and the diagnostic accuracy of CRP was assessed post-hoc. Results: Dogs with BC had lower median CRP (1.04 mg/dL; range, 0.08-7.21) than those with APy (23.65 ± 11.96 mg/dL; median difference [MD], 22.9 mg/dL; 95% CI, 18.2-26.5; P < .001) and APr (20.9 mg/dL; range, 5.93-55.97; MD, 19.9 mg/dL; 95% CI, 10.7-25.6; P < .001), whereas APy and APr did not differ (MD, -3.0 mg/dL; 95% CI, -10.6 to 4.4; P > .99). Serum CRP concentration had high discriminative ability to differentiate dogs with BC and APy, APr, or both (area under the curve [AUC], 0.99; 95% CI, 0.99-1). Conclusions and clinical importance: Serum CRP concentration evaluated at diagnosis, when highly increased, may help differentiate BC from APy in dogs without concurrent inflammatory diseases.