Scoping Review Finds Major Gaps in How Vets Diagnose and Treat Pyelonephritis in Cats and Dogs

Bacterial pyelonephritis, an infection of the kidney that is usually caused by bacteria ascending from the lower urinary tract, is widely regarded as a potentially life-threatening but often treatable condition in both dogs and cats. Yet according to a new scoping review published in BMC Veterinary Research, the scientific literature on this disease is far thinner and far more fragmented than many clinicians might assume. After systematically searching five bibliographic databases, a team of Swedish researchers identified 176 original studies covering spontaneous pyelonephritis in the two species, and concluded that the field lacks universally accepted clinical diagnostic criteria, contains no clinical trials of antimicrobial or other treatments, and offers almost no data on long-term outcomes for affected animals.

The review, led by L. Pelander together with C. Ekstrand and K. Scahill, was designed to map the volume, nature and characteristics of published research on pyelonephritis in dogs and cats, to collate case definitions and diagnostic criteria, antibacterial regimens and reported outcomes, and to identify knowledge gaps that should shape future research. The study protocol was drafted using the PRISMA-ScR reporting guidelines and registered prospectively with SYREAF, the Systematic Reviews for Animals and Food registry, in March 2023. The authors report that no substantial deviations were made from the registered protocol.

The search itself was extensive. An initial search performed on 22 March 2023 across Biosis, CAB Abstracts, Medline, Web of Science Core Collection and Scopus identified 6,443 references, which reduced to 3,994 unique records after duplicates were removed. A second search on 5 February 2025 added a further 315 unique studies, bringing the total number of records screened at title and abstract level to 4,309. Reference lists of recent review texts and chapters in four companion animal medicine textbooks were also screened. To be included, studies had to be written in English or German and report on any aspect of spontaneous pyelonephritis in cats or dogs, including risk factors, signalment, history, clinical findings, diagnostic criteria, treatment, prognosis and outcome. Studies of experimentally infected animals, infections with Leptospira species, and research in people were excluded, although case reports were eligible.

The final evidence base comprised 176 studies involving approximately 1,600 cats and dogs with pyelonephritis. Notably, 817 of those animals came from just two retrospective studies of prescription data in dogs and cats diagnosed with upper or lower bacterial urinary tract infections at veterinary practices in the USA and Canada. One hundred and fifty-five of the included studies concerned dogs, 55 concerned cats, and six covered both species. The publications spanned the years 1954 to 2025, with an increase in publication numbers over the last decade. Geographically, the United States dominated with 60 studies, followed by Germany with 19, India with 15, the United Kingdom with 14, Australia with 11, Canada with 10 and Korea with 10, while the remaining 37 studies came from 14 other countries.

Perhaps the most striking structural finding of the review is that the literature effectively describes three distinct entities under one disease label: histologically diagnosed pyelonephritis, clinically diagnosed pyelonephritis, and pyonephrosis, the accumulation of purulent material in the renal pelvis secondary to an obstruction. Histopathology studies, typically based on necropsy or biopsy series, included both acute suppurative and chronic renal interstitial patterns, frequently alongside other urinary tract pathology such as ectopic ureters. Because case identification in these studies was often post-mortem and clinical information was limited, the authors note that some of these cases are likely to have been subclinical. The pyonephrosis literature, by contrast, focused on obstructive, pus-filled renal pelves and described renal-sparing interventions such as retrograde ureteropelvic lavage with ureteral stenting in dogs and subcutaneous ureteral bypass devices in cats, but only short-term clinical resolutions were documented.

In terms of study design, the review identified 95 observational studies and 81 case reports, but not a single clinical trial. Only one meta-analysis was found, which investigated mortality in dogs and cats with acute kidney injury by aetiology and suggested higher rates of overall mortality in animals with noninfectious causes relative to infectious causes. Clinical diagnostic criteria for pyelonephritis were provided in only 19 of the 176 studies, and those criteria were markedly heterogeneous. Most combined elements from two or more of four domains: microbiology, most often a positive urine culture obtained by cystocentesis, with a minority using pyelocentesis as a reference standard; clinical signs such as lethargy, inappetence, vomiting, fever and renal or abdominal pain; clinicopathological abnormalities including azotaemia, leucocytosis, a left shift or increased acute phase proteins; and imaging findings such as renal pelvic dilation, proximal ureteral dilation, hyperechoic cortices and retroperitoneal changes. The authors argue that this variation produces different clinical populations across studies, making evidence synthesis and generalisation difficult.

The diagnostic evidence that does exist is limited and, in places, sobering. Six studies evaluated diagnostic tests. Two feline studies assessed serum amyloid A, an acute phase protein: one found that a value above 51.3 mg/L was suggestive of pyelonephritis in cats with suspected or confirmed disease, while another found the marker could not discriminate among groups of cats with kidney injury of different causes, although all four azotaemic cats with pyelonephritis in that study had values above 100 mg/L. Two studies explored urinary microRNA profiles as potential discriminatory markers, identifying differentially abundant microRNAs between cats with pyelonephritis and controls or other urological conditions. Imaging fared less well. In two studies with comparator groups, renal pelvic width measured ultrasonographically overlapped substantially across animals with normal renal function, nonobstructive urinary tract disease and obstructive disease, and in cats, ultrasonographic features overlapped considerably among stable chronic kidney disease, clinically diagnosed pyelonephritis and ureteral obstruction. Taken together, the authors conclude that renal pelvic or proximal ureteral width on ultrasound should not be used as a standalone diagnostic test for pyelonephritis.

Treatment evidence is equally sparse. No prospective trials have compared the efficacy of different antibacterial substances or treatment durations in dogs or cats. In the only cohort-level treatment data, from a study of 32 cats with pyelonephritis by Whitehouse et al., the median treatment duration was 29 days, ranging from 10 to 62 days. In that same cohort, among 12 cats with post-therapy cultures, bacteriologic cure occurred in 10. In that cohort, survival to discharge was 94 percent (29/31), and three-month survival among cats with follow-up was 70 percent (14/20), with non-survivors showing higher admission creatinine, BUN and phosphorus concentrations. Across 81 case reports covering 93 animals, amoxicillin/clavulanic acid and fluoroquinolones were the most frequently used antibacterials, with reported durations typically ranging from two to six weeks, but no reliable efficacy comparisons were possible because cases varied widely in severity and reporting detail.

The treatment-duration question carries real weight, because fluoroquinolones are recommended internationally for pyelonephritis in both species yet are classified as critically important in human medicine, and the European Medicines Agency holds that their use in animals should be restricted to mitigate public health risk, one reason the authors give for keeping overdiagnosis to a minimum. Reported veterinary durations of two to six weeks contrast with the current recommendation of 10 to 14 days, and with human systematic reviews indicating that five to seven days are as effective as longer courses for acute uncomplicated pyelonephritis in adults. The authors call for randomised veterinary trials comparing shorter with longer durations, stratified by drug class, alongside work to establish agreed clinical diagnostic criteria and core outcome sets. Information on short-term outcomes was scarce and long-term renal functional data were described as virtually absent, leaving the long-term impact of pyelonephritis on kidney health unclear. The review’s limitations include its restriction to English and German publications and the absence of any search for grey literature.

Subject of Research: Diagnostic criteria, antimicrobial treatment and outcome reporting for bacterial pyelonephritis in dogs and cats

Article Title: Pyelonephritis in cats and dogs – a scoping review

Article References: Pelander, L., Ekstrand, C., & Scahill, K. (2026). Pyelonephritis in cats and dogs – a scoping review. BMC Veterinary Research, 22(1), Article 635. https://doi.org/10.1186/s12917-026-06042-1

Image Credits: AI Generated

DOI: 10.1186/s12917-026-06042-1

Keywords: pyelonephritis, dogs, cats, veterinary medicine, scoping review, antimicrobial treatment, diagnostic criteria, urinary tract infection, pyonephrosis, ultrasound, fluoroquinolones, knowledge gaps