The condition can be hard to distinguish from other urological issues.

New research has identified serum amyloid A (SAA) as an accurate biomarker of pyelonephritis in cats.

Researchers describe SAA as having ‘high diagnostic accuracy’, which could support veterinary surgeons in distinguishing pyelonephritis from other urological conditions.

Pyelonephritis is a serious bacterial infection of the kidneys, caused by bacteria from the lower urinary tract. It is considered challenging to diagnose, with its clinical signs overlapping with conditions such as chronic disease and ureteral obstruction.

The diagnosis of the condition will usually rely on a positive bladder urine culture. This is considered alongside clinical, laboratory or ultrasonographic signs usually suggestive of upper urinary tract infections.

To improve the diagnostic process of identifying pyelonephritis, researchers studied how SAA and leukocyte ratios may help distinguish between the condition and other similar urological diseases.

The research team, from the University of Copenhagen, analysed the urine and blood samples of 71 cats. The cats had either been enrolled in this study from 2020-2024, or enrolled in previous studies from 2015-2019 with stored urine and blood samples.

Cats were either classified as having confirmed pyelonephritis, presumptive pyelonephritis, having other urological disorders or being clinically healthy. Serum amyloid A was assessed at enrolment, with neutrophil:lymphocyte and monocyte:lymphocyte ratios calculated for each cat.

The median SAA concentrations were found to be significantly higher in cats with confirmed pyelonephritis and presumptive pyelonephritis. There was minimal overlap compared to cats which had other urological conditions or healthy cats.

Following antimicrobial treatment, SAA levels went on to decline and normalise in the vast majority of cats. 

Meanwhile the neutrophil:lymphocyte and monocyte:lymphocyte ratios, despite being significantly higher in cats with pyelonephritis, had a substantial overlap with other urological conditions. This limited their usefulness as a diagnostic tool.

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 full study can be found in the Journal of Small Animal Practice.

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