Biomarker shows high diagnostic accuracy for pyelonephritis in cats, study finds

8 July 2026

A new study has identified serum amyloid A (SAA) as a highly accurate biomarker for distinguishing pyelonephritis in cats from other urological conditions.

Pyelonephritis is challenging to diagnose, as its clinical signs often overlap with other urological disorders, such as chronic kidney disease and ureteral obstruction. Diagnosis typically relies on a positive bladder urine culture coupled with clinical, laboratory and/or ultrasonographic signs suggestive of upper urinary tract infection.

Published in the Journal of Small Animal Practice, the study assessed whether SAA and leukocyte ratios could help differentiate pyelonephritis from other urological diseases.

Researchers at the University of Copenhagen’s University Hospital for Companion Animals analysed urine and blood samples from 71 cats. Cats were classified as having confirmed pyelonephritis (based on a positive urine culture from the renal pelvis), presumptive pyelonephritis (based on positive bladder urine culture plus clinical and/or clinicopathological findings), having other urological disorders (chronic kidney disease, ureteral obstruction, cystitis, subclinical bacteriuria, or a combination of these), or being clinically healthy. Serum amyloid A (SAA) was measured at enrolment and neutrophil:lymphocyte and monocyte:lymphocyte ratios were calculated for each cat.

Median SAA concentrations were significantly higher in cats with pyelonephritis (180.3 mg/L) and presumed pyelonephritis (607.4 mg/L), with minimal overlap compared to cats with other urological conditions (0.4 mg/L) or healthy cats (0.0 mg/L).

SAA levels declined and normalised in the vast majority of cats following antimicrobial treatment. Although neutrophil:lymphocyte and monocyte:lymphocyte ratios were also significantly higher in cats with pyelonephritis than in healthy cats, these measurements had substantial overlap with other urological conditions, limiting their diagnostic usefulness.

The findings suggest that at a threshold of 49 mg/L, SAA offers a highly accurate, non-invasive tool to improve diagnostic confidence. An SAA concentration above 50 mg/L increases the likelihood of pyelonephritis in cats with urological disease, whereas concentrations below 50 mg/L make pyelonephritis less likely.

Dr Lisbeth Jessen, lead author of the study, said: “Our findings closely align with those reported by the French research group led by Kurtz et al. 2024, who also identified SAA as a useful indicator of pyelonephritis at a similar threshold of 51 mg/L. This consistency strengthens our confidence in the robustness of the results. As an acute-phase protein, SAA is not specific to pyelonephritis, and results should always be interpreted alongside other clinical and paraclinical findings”.

The study also found elevated urinary kidney injury marker-1 in more than half of cats with pyelonephritis and in those with ureteral obstruction. This suggests that proximal tubular injury is common in cats with pyelonephritis, although the clinical implications require further investigation.

Read the study in the Journal of Small Animal Practice: https://onlinelibrary.wiley.com/doi/10.1111/jsap.70140