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

Markedly elevated serum CRP reliably differentiates acute pyelonephritis from bacterial cystitis in dogs.

This retrospective observational study evaluated the utility of serum C-reactive protein (CRP) in differentiating acute pyelonephritis (APy) from bacterial cystitis (BC) and acute prostatitis (APr) in dogs. One hundred fifteen client-owned dogs with positive urine cultures were enrolled and categorized into three groups: BC (n=56), APy (n=32), and APr (n=23), with four dogs presenting with concurrent APy and APr. Dogs with comorbidities known to affect CRP concentrations and those with subclinical bacteriuria were excluded. Dogs with BC had significantly lower median serum CRP (1.04 mg/dL) compared to those with APy (23.65 ± 11.96 mg/dL) and APr (20.9 mg/dL), with both differences reaching statistical significance (P < .001). No significant difference in CRP was observed between APy and APr groups. Post-hoc diagnostic accuracy analysis demonstrated that serum CRP had excellent discriminative ability to differentiate BC from upper urinary tract or prostatic infections (AUC = 0.99; 95% CI, 0.99–1.00). The authors conclude that markedly elevated serum CRP at diagnosis may serve as a clinically useful biomarker to distinguish BC from APy or APr in dogs without concurrent inflammatory diseases. This is particularly relevant given that clinical signs and urinalysis findings can overlap between these conditions, and definitive diagnosis often requires advanced diagnostics such as imaging or renal pelvis culture.

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