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. 2026 Oct 5;40(5):aalag232. doi: 10.1093/jvimsj/aalag232

Retrospective evaluation of lipiduria in urine from 140 dogs and 74 cats

Mario Cervone 1,✉, Damien Legroux 2,3, Gaelle Barral 4, Eve Ramery 5,6
PMCID: PMC13637813  PMID: 42832652

Abstract

Background

Lipiduria has recognized physiopathological and diagnostic relevance in human medicine, while data regarding its relevance in animals remain limited.

Hypothesis/Objectives

To determine the frequency of lipiduria in dogs and cats and to assess whether lipiduria represents an epiphenomenon or is associated with animal-related factors.

Animals

Urinalysis results from 140 dogs and 74 cats.

Methods

Retrospective study. Cases were included if complete urinalysis data were available. Animals were classified as lipiduric or non-lipiduric. Animal characteristics, as well as selected hematologic and urinary abnormalities, were compared between groups. In dogs, factors potentially associated with the presence of lipiduria were further evaluated using multivariable logistic regression analysis.

Results

Overall, 58% (125/214) animals were lipiduric, including 46% (64/140) dogs and 82% (61/74) cats. Lipiduria was significantly more frequent in cats (82%) than in dogs (46%) (P < .00001). Among cats, lipiduric individuals were older (mean age 9.5 years; SD ± 4.5; P = .02). In dogs, females (63%; 40/64) were overrepresented in the lipiduric group (P = .0008). Lipiduric dogs had a higher mean urine pH (6.4; SD ± 1.2; P = .00054) and more frequently exhibited struvite crystalluria (17%; 11/64; P = .003). In multivariable analysis, female dogs had 3.5-fold higher odds of lipiduria (OR, 3.5; 95% CI, 1.7-7.3), and the odds of lipiduria increased by 5% for each 0.1-unit increase in urine pH.

Conclusions and clinical importance

Lipiduria was a common finding in this study, particularly in cats. In dogs, our findings suggest a potential link between lipiduria, female status, and high urine pH.

Abstract Translated to French

Contexte

Les données concernant la signification clinique de la lipidurie chez les chiens et les chats restent limitées.

Objectifs

Déterminer la fréquence de la lipidurie chez le chien et le chat et évaluer si elle présente un caractère pathologique.

Animaux

Analyses urinaires chez 140 chiens et 74 chats.

Méthodes

Étude rétrospective. Les animaux étaient inclus lorsqu’une analyse urinaire complète était disponible et étaient classés comme lipiduriques ou non lipiduriques. Les caractéristiques des animaux et certaines anomalies biologiques, ont été comparées entre les animaux lipiduriques et non lipiduriques. Chez le chien, des facteurs potentiellement associés à la lipidurie ont été évalués.

Résultats

Cinquante-huit % (125/214) des animaux présentaient une lipidurie, qui était significativement plus fréquente chez les chats (82%; 61/74) que chez les chiens (46%; 64/140) (P < .00001). Les chats lipiduriques étaient plus âgés (âge moyen: 9,5 ans; SD ± 4,5; P = .02). Les chiennes lipiduriques étaient surreprésentées (63%; 40/64; P = .0008). Les chiens lipiduriques présentaient un pH urinaire moyen plus élevé (6,4; SD ± 1,2; P = .00054) et plus fréquemment des struvites (17%; 11/64; P = .003). En analyse multivariée, les chiennes présentaient une probabilité de lipidurie 3,5 fois plus élevée (OR, 3.5; 95% CI, 1.7-7.3), et les chances de présenter une lipidurie augmentaient de 5 % pour chaque augmentation de 0,1 unité du pH urinaire.

Conclusions et relevance clinique

La lipidurie était fréquente dans cette étude, particulièrement chez les chats. Chez le chien, les résultats suggèrent une association potentielle entre la lipidurie, le sexe femelle et un pH urinaire plus élevé.

Keywords: fat, lipids, nephropathy, obesity, urine

Introduction

Lipid metabolism is recognized as a key contributor to the progression of human chronic kidney disease (CKD).1 Lipiduria is reported in association with a variety of renal disorders, including both glomerular and tubular diseases.2,3 In contrast, only minimal amounts of lipids are typically detected in the urine of healthy individuals.2 More recently, lipiduria has emerged as a potential predictor of specific histopathological lesions on renal biopsy.4 Urinary lipids might also play a role in urinary stone formation by facilitating crystal nucleation and contributing to calcification processes.5,6 Furthermore, elevated urinary concentrations of specific lipid compounds have been documented in human patients with bacterial cystitis and interstitial cystitis/bladder pain syndrome, also suggesting a possible relationship between urinary lipid and inflammatory diseases affecting the lower urinary tract.7

In veterinary medicine, lipiduria is commonly identified on urine sediment examination and abdominal ultrasonography (AUS) in both cats and dogs.8–10 However, despite its apparent frequency, it has been only sparsely investigated. Lipiduria in cats is proposed to originate from tubular shedding, as felids physiologically store lipids (including triglycerides, phospholipids, and cholesterol) within epithelial cells of the proximal convoluted tubule.11–16 An age-associated increase in renal lipid content is reported in clinically healthy cats.16 However, lipid infiltration of the renal interstitium is described in up to 90% of cats with CKD, whereas it is absent in cats without CKD.17–19 Notably, interstitial lipid accumulation is consistently associated with renal inflammatory changes in both healthy and CKD-affected cats.16,18 Collectively, these findings support a potential role for lipid-mediated toxicity in pathogenesis of CKD in cats, possibly through promotion of tubular degeneration and atrophy. In dogs, urinary lipid metabolites are investigated in the context of hepatic masses,20 and, as in cats, from an ultrasonographic perspective.10,21 Lipiduria was identified in up to 77% of dogs.10

Given the paucity of data regarding lipiduria in cats, and even more so in dogs, as well as the conflicting evidence concerning the role of lipids in renal disease in dogs and cats, the primary objective of this retrospective study was to describe the frequency of lipiduria in cats and dogs. In addition, we sought to determine whether lipiduria represents an epiphenomenon or is associated with selected urinalysis variables, and whether its frequency and magnitude are influenced by animal-related factors. We hypothesized that lipiduria is a common finding in both dogs and cats.

Materials and methods

Urinalysis results of urine collected from dogs and cats admitted to a private veterinary referral centre between January 2021 and June 2022 were retrospectively reviewed. Cases were included only if complete urinalysis results were available (Appendix). Animals were categorized as lipiduric or non-lipiduric based on the presence or absence of lipid droplets in urine, respectively. For each animal, signalment, body weight and body condition score (BCS), urine collection method, urinalysis results, plasma creatinine (pCreat) and total cholesterol (tChol) concentrations (where available), and the final diagnosis were recorded. Final diagnoses were classified into urinary, gastrointestinal, hepato-pancreatic, endocrine, inflammatory/infectious, neoplastic, or miscellaneous. Body condition score was assessed using a 5-point scale.22 In dogs, renal azotemia was diagnosed based on the combination of urine specific gravity (USG) < 1.030 and increased pCreat concentration.23 Because cats with naturally occurring CKD might retain their urine concentrating ability,24 renal azotemia was diagnosed based only on pCreat concentration. Overall, azotemia was defined as pCreat higher than 14 mg/L in dogs and 16 mg/L in cats.23

Data were analyzed using SPSS Statistics® and 2 online calculators.1,2 Data are presented as mean when normally distributed and as median otherwise. The frequency of crystalluria, proteinuria, pyuria, bacteriuria, and hematuria was compared between lipiduric and non-lipiduric animals using Fisher’s exact test or the χ-square test, as appropriate. Continuous variables were compared between groups using the Student’s t-test for normally distributed data or the Mann–Whitney U test for non-normally distributed data. Statistical significance was set at P < .05. Univariate logistic regression analysis was performed to assess the association between lipiduria and age, sex, BCS, USG, urine pH, as well as the presence of hypercholesterolemia, azotemia, crystalluria, proteinuria, pyuria, bacteriuria, and hematuria. Subsequently, 2 multivariable logistic regression models were constructed. The first model included variables potentially influencing the presence of lipiduria (age, sex, BCS, azotemia, and hypercholesterolemia), whereas the second model included variables that could be affected by lipiduria (USG, urine pH, azotemia, crystalluria, proteinuria, pyuria, bacteriuria, and hematuria). Variables with a P ≤ .20 in univariate analyses were considered for inclusion in the multivariable models. Multivariable logistic regression analyses were performed only in dogs because of the limited number of cats, particularly in the non-lipiduric group.

Results

Signalment and BCS

Complete urinalysis results from 214 out of 248 animals were included in this retrospective study. Thirty-four samples were excluded because of incomplete urinalysis results. There were 140 dogs and 74 cats. Breeds are presented in Supplementary Materials 1. The mean age was of 7.4 years (SD ± 4) among dogs, and of 8.7 years (SD ± 4.8) among cats. Among dogs, 47% (66/140, including 52 spayed dogs) were female, and 52% (73/140, including 30 castrated dogs) were male. The sex was not reported in 1 dog. Among cats, 59% (44/74, including 41 castrated cats) were male, and 41% (30/74) were spayed females. Overall, 58% (125/214) animals were lipiduric, while 42% (89/214) were non-lipiduric, including 46% (64/140) lipiduric dogs and 82% (61/74) lipiduric cats. Overall, lipiduria was significantly (P < .00001) more frequent in cats compared to dogs.

For dogs, the mean age was not significantly different between lipiduric (7.5 years; SD ± 3.6) and non-lipiduric (7.3 years; SD ± 4.3) animals; while lipiduric cats (mean age of 9.5 years; SD ± 4.5) were significantly older (P = .02) compared to non-lipiduric ones (mean age of 6.2 years; SD ± 5.4) (Table 1). In the canine group, females (63%) were overrepresented among lipiduric dogs (P = .0008), while no difference about sex was found in cats. Among dogs, the median BCS was of 3/5 (range: 1-5), with no difference in median BCS between lipiduric (3/5; range: 1-5) and non-lipiduric (3/5; range: 1.5-5) animals. Among cats, the median BCS was of 2.5/5 (range: 1-5), with no difference in median BCS between lipiduric (2.5/5; range: 1/5) and non-lipiduric (2.5/5; range: 2-4) animals.

Table 1.

Signalment and body condition score (BCS) (5-point scale) of lipiduric and non-lipiduric dogs and cats.

Lipiduric Non-lipiduric P-value
Cats
Age, years (mean ± SD) 9.5 ± 4.5 6.2 ± 5.4 .02
Sex (n) 35 males; 26 females 9 males; 4 females .5
BCS (median with range) 2.5 (1-5) 2.5 (2-4) .6
Dogs
Age, years (mean ± SD) 7.5 ± 3.6 7.3 ± 4.3 .80
Sex (n) 24 males; 40 females 50 males; 26 females .0008
BCS (median with range) 3 (1-5) 3 (1.5-5) .2
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Statistically significant (P < .05) results are in bold.

Urinalysis results

Refractometry and dipstick urinalysis results are shown in Table 2. The urine collection method was known for 110/140 dogs and 76/78 cats. In the dogs, urine samples were collected by cystocentesis in 88% (97/110) dogs, while spontaneous voiding was reported in 11% (12/110) dogs. In the cats, urine samples were collected by cystocentesis in 97% (74/76) cats, while spontaneous voiding was reported in 1 cat and collection at the SUB port in another cat.

Table 2.

Urine specific gravity (USG), dipstick urinalysis, and sediment examination results in lipiduric and non-lipiduric dogs and cats.

Lipiduric Non-lipiduric P-value
Cats
USG (mean ± SD) 1.040 ± 0.013 1.030 ± 0.016 .2
pH (mean ± SD) 5.8 ± 0.74 5.8 ± 0.80 .1
Proteinuria, % (n)  
Median (IQR) 		88% (54/61) 1 (0) 100% (13/13) 1 (0) .37
Hematuria % (n) 57% (33/61) 46% (5/13) .6
Pyuria, % (n)  
Median (IQR) 		34% (21/61) 0 (1) 23% (3/13) 0 (0) .45
Bacteriuria % (n) 6% (4/61) 8% (1/13) 1
Dogs
USG (mean ± SD) 1.030 ± 0.013 1.027 ± 0.013 .1
pH (mean ± SD) 6.8 ± 1.17 6.1 ± 1.18 .00054
Proteinuria, % (n)  
Median (IQR) 		80% (51/64) 1 (1) 75% (57/76) 1 (1.25) .57
Hematuria % (n) 42% (27/64) 50% (38/76) .8
Pyuria, % (n)  
Median (IQR) 		70% (45/64) 0 (1) 64% (49/76) 0 (1) .53
Bacteriuria % (n) 6% (4/64) 6% (5/76) 1
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Statistically significant (P < .05) results are in bold.

In dogs, the overall mean USG was 1.030 (SD ± 0.013), with no difference between lipiduric (1.030; SD ± 0.013) and non-lipiduric (1.027; SD ± 0.013) dogs. In cats, the overall mean USG was 1.040 (SD ± 0.014), with no difference between lipiduric (1.040; SD ± 0.013) and non-lipiduric (1.030; SD ± 0.016) cats.

In dogs, the overall mean urine pH was 6.4 (SD ± 1.2), with a significant (P = .00054) higher urine pH in lipiduric dogs (6.8; SD ± 1.17) compared to non-lipiduric dogs (6.1; SD ± 1.18). In cats, the overall mean urine pH was 5.8 (SD ± 0.74), with no difference between lipiduric (5.8; SD ± 0.74) and non-lipiduric (5.8; SD ± 0.80) cats.

Concerning the other urinalysis results, neither the frequency of proteinuria, hematuria, pyuria, and bacteriuria, nor median proteinuria and pyuria differed between lipiduric and non-lipiduric animals, in both dogs and cats.

At urine cytology, 41% dogs (58/140) and 15% cats (11/74) had urine crystals. Among dogs, 11% had struvites (15/140) crystals, 25% had calcium oxalate (CaOx) crystals (25/140), and 7% had bilirubine crystals (12/140) (Table 3). Four dogs had both CaOx and struvite crystalluria. There was no difference in the overall urinary crystal frequency between lipiduric (42%) and non-lipiduric (41%) animals. However, lipiduric dogs had more frequently (P = .003) struvites crystals (17%; 11/64) compared to non-lipiduric ones (5%; 4/76). Moreover, bilirubine crystals were significantly (P = .0005) more frequent in non-lipiduric dogs (16%; 12/76) compared to lipiduric dogs (0%; 0/64). The frequency of CaOx crystals was similar between lipiduric (28%; 18/64) and non-lipiduric (22%; 17/76) dogs (Table 3).

Table 3.

Frequency of urinary crystals in lipiduric and non-lipiduric dogs and cats.

Lipiduric Non-lipiduric P-value
Cats
Struvite, % (n) 8% (5/61) 0% (0/13) .6
Calcium oxalate, % (n) 3% (2/61) 8% (1/13) .4
Urates, % (n) 2% (1/61) 8% (1/13) .3
Bilirubin, % (n) 2% (1/61) 0% 0/13) 1
Dogs
Struvite, % (n) 17% (11/64) 5% (4/76) .003
Calcium oxalate, % (n) 28% (18/64) 22% (17/76) .4
Urates, % (n) 0% (0/64) 0% (0/76) 1
Bilirubin, % (n) 0% (0/64) 16% (12/76) .0005
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Statistically significant (P < .05) results are in bold.

In the cats, 7% had struvites crystals (5/74), 4% (3/74) had CaOx crystals, 1% (1/74) had urate crystals, and 3% (2/74) had non-classified crystals. There was no difference in the overall urinary crystal frequency between lipiduric (15%) and non-lipiduric (15%) cats. Furthermore, no difference was found in the frequency of specific crystal types between lipiduric and non-lipiduric cats (Table 3).

Bloodwork results

Plasma creatinine concentration was measured in 136 dogs (including 61 lipiduric and 75 non-lipiduric dogs), and in 74 cats (including 61 lipiduric and 13 non-lipiduric cats). The median pCreat concentration was of 10 mg/L (ranging between 2 and 50 mg/L) in dogs, and of 17 mg/L (ranging between 4 and 40 mg/L) in cats. The median pCreat concentration was similar between lipiduric and non-lipiduric animals, in both dogs and cats. Overall, 11% dogs (15/136; including 4 lipiduric and 11 non-lipiduric dogs) and 72% cats (53/74; including 45 lipiduric and 13 non-lipiduric cats) had azotemia. No difference was found in the frequency of azotemia between animals with and without lipiduria (P = 0.18), neither in dogs nor in cats.

Plasma tChol concentration was measured in 97 dogs (including 38 lipiduric and 59 non-lipiduric dogs), and in 50 cats (including 42 lipiduric and 8 non-lipiduric cats). The mean plasma tChol concentration was of 2.3 g/L (SD ± 1.06) in dogs, and of 1.6 g/L (SD ± 0.61) in cats, without difference between lipiduric and non-lipiduric animals. Hypercholesterolemia (tChol > 3.2 mg/L) was present in 10% dogs (10/97), without difference (P = .4) between lipiduric (13%; 5/38) and non-lipiduric (8%; 5/59) animals. No cats had hypercholesterolemia.

Magnitude of lipiduria and its correlation with putative variables

The median lipiduria (see Appendix) was not significantly different between dogs (1.5; ranging between 0.5 and 3) and cats (0.5; ranging between 1 and 3), including 9% dogs (6/64) and 2% cats (1/61) with fair lipiduria, 67% dogs (43/64) and 56% cats (34/61) with mild lipiduria, 28% dogs (18/64) and 38% cats (23/61) with intermediate lipiduria, 28% dogs (18/64) and 34% cats (21/61) with frequent lipiduria, 9% dogs (6/64) and 18% cats (11/61) with very frequent lipiduria, and 1% dogs (1/64) and 8% cats (5/61) with severe lipiduria. The magnitude of lipiduria did not correlate with the age, the BCS, the pCreat concentration, nor with the plasma tChol concentration, neither in dogs nor in cats (Supplementary Materials 2).

Multivariable logistic regression in dogs

At univariable analysis, the female sex (<.01), the mean BCS (P = .2), the mean USG (P = .1), the mean urinary pH (P < .001), and the mean pCreat concentration (P = .2) were significantly associated with the presence of lipidura. In the first multivariable model, only female sex remained independently associated with lipiduria (P < .001), with female dogs having approximately 3.5 times the odds of lipiduria compared with male dogs. In the second multivariable model, only urinary pH remained independently associated with lipiduria (P < .01). Odds of having lipiduria increased by a factor of 1.05 per 0.1 unit of urinary pH increase.

Final diagnoses

The diseases finally diagnosed are summarized in the Figure 1. Overall, the frequency of each disease category was similar in lipiduric and non-lipiduric animals, in both dogs and cats.

Figure 1.

For image description, please refer to the figure legend and surrounding text.

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Frequency of disease category in lipiduric and non-lipiduric dogs and cats. No statistically significant differences were identified between groups.

Discussion

This is a large-scale study evaluating the frequency of lipiduria in both dogs and cats, and assessing its potential associations with epidemiological and clinicopathological variables. Lipiduria was identified as a common finding in both species, but it was more common in cats, as hypothesized. Overall, lipiduric cats were significantly older, whereas a higher proportion of lipiduric dogs were female. On urinalysis, dogs with lipiduria exhibited a higher urine pH, a greater frequency of struvite crystalluria, and a lower frequency of bilirubin crystals. No significant association was observed with BCS or concurrent diseases.

As previously described, lipiduria was a common finding in both dogs and cats in the present study, with a higher prevalence observed in cats.8,10,16 In cats, it is proposed that lipid droplets identified in urine sediment originate from tubular epithelial shedding, either as part of normal cellular turnover or secondary to tubular injury.8,16 In a study evaluating the ultrasonographic appearance of lipiduria in cats, lipids were detected in 90% (36/40) of cases, most of which were clinically healthy cats and had unremarkable urinalysis findings.21 In that cohort, lipiduria consisted predominantly of cholesterol esters, triglycerides, and phospholipids, with smaller quantities of diacylglycerol, cholesterol, and free fatty acids. In humans, only minimal amounts of cholesterol esters and phospholipids are detected in the urine of healthy individuals, whereas increased lipid excretion is more commonly associated with nephrotic syndrome, hyperlipidemia, and CKD.3,25–29

In the present study, the distribution of disease categories did not differ significantly between lipiduric and non-lipiduric animals. These findings align with those of previous retrospective studies in cats.8,21 However, the absence of association between lipiduria and concomitant pathological conditions observed in our study should be interpreted with caution, as only diseased animals were included. In addition, the lack of lipid characterization by chromatographic techniques precluded a more detailed evaluation of the biochemical composition of urinary lipids and their potential diagnostic or pathological relevance.

In the present study, lipiduric cats were significantly older than non-lipiduric cats, while no difference was found among dogs. The older feline cohort among lipiduric cats is consistent with previous reports documenting an increased prevalence of both lipiduria and renal interstitial lipid accumulation in aged cats, with more extensive lipid deposition identified in older individuals.16,18 Such findings might suggest that renal lipid accumulation occurs progressively over time, potentially because of repeated episodes of tubular injury and subsequent release of lipids after disruption of tubular epithelial cell membranes.18 Supporting this hypothesis, 1 study demonstrated that cyclooxygenase-derived metabolites constitute a substantial proportion of urinary lipid metabolites in healthy cats,30 further highlighting the potential link between lipid metabolism, inflammatory conditions, renal pathology, and age-related changes.

In our study, no sex predisposition was identified in cats, whereas female dogs were overrepresented among lipiduric individuals. Interestingly, histopathological investigations have shown that the most extensive interstitial lipid deposition might occur in female cats, which could suggest a potential sex-related susceptibility to renal lipid accumulation.18 This observation might, in part, provide a biological rationale for the higher frequency of lipiduria observed in female dogs in the present study.

We identified no association between azotemia and urinary lipid droplet shedding in either dogs or cats. This finding is consistent with a previous work.8 However, feline necropsy studies have reported that interstitial lipid accumulation is relatively common and frequently associated with focal inflammatory lesions on renal histopathology.16,18 This phenomenon has been attributed to disruption of the tubular basement membrane in the context of tubular injury.19,31 Lipids have been proposed to act as pro-inflammatory mediators, potentially contributing to or accelerating the progression of CKD.32–34 Based on this hypothesis, one might expect azotemia to be more prevalent in animals with lipiduria. Supporting this concept, a necropsy study including both dogs and cats reported an absence of microscopic renal lipid deposition in animals without CKD.18 Serum creatinine is known to lack sensitivity for the detection of early renal dysfunction.35,36 This limited sensitivity might explain why animals with lipiduria, even when marked, can remain non-azotemic.

In the present study, dogs (but not cats) with lipiduria exhibited a significantly higher mean urinary pH compared with their non-lipiduric counterparts. Urinary pH is inherently variable and influenced by multiple factors.37 In dogs, an alkaline urinary environment has been associated with an increased risk of urolith formation, particularly struvite. Interestingly, an increase of urinary struvites crystals was also noticed in the present study.38 In human medicine, persistently elevated urinary pH has been linked to proximal tubular alterations affecting cellular acid–base handling.39 Moreover, increased urinary lipid excretion has been associated with tubular oxidative stress and tubular injury.16,40 Taken together, these observations raise the hypothesis that lipiduria could reflect, or contribute to, tubular injury, potentially resulting in impaired urinary acidification and consequently higher urinary pH in affected dogs. However, this interpretation remains speculative and warrants further investigation. Moreover, although the difference in urinary pH between lipiduric and non-lipiduric dogs reached statistical significance, the magnitude of this difference was small and is unlikely to be clinically relevant. The risk of canine struvite urolithiasis is generally higher with more alkaline urine (typically pH > 7), although struvite uroliths are reported in dogs with lower urinary pH values.38

Lipiduric dogs in the present study exhibited a higher prevalence of struvite crystalluria and a lower frequency of bilirubin crystals compared with non-lipiduric dogs. The increased occurrence of struvite crystals might, at least in part, be explained by the higher mean urinary pH observed in lipiduric dogs, given the well-established association between alkaline urine and struvite formation.38 Beyond pH-related effects, lipid metabolism has been increasingly implicated in lithogenesis in both human and veterinary medicine.40–43 Moreover, obese cats have an increased risk for struvite uroliths.44 In humans, lipids are commonly identified within the stone matrix and are thought to contribute to stone formation processes.40 Experimental data indicate that lipid-rich matrices might act as a nidus for mineral nucleation.45 Consistent with these findings, human studies have demonstrated increased urinary excretion of lipids in patients with urolithiasis, in individuals with calcium oxalate stones, compared with controls.45,46 The lower prevalence of bilirubin crystalluria observed in lipiduric dogs in this study might be sex-related, as most lipiduric dogs were females. In male dogs, renal tubular epithelial cells can conjugate bilirubin, and the presence of bilirubin in urine is therefore more commonly encountered physiologically than in females.47

In dogs, hypertriglyceridemia has been associated with an increased risk of CaOx urolithiasis.43 The same has been reported in human patients with dyslipidemia.48 In addition, recent metabolomic data in dogs suggest that upregulation of the glycerophospholipid metabolic pathway might be involved in the pathogenesis of struvite urolithiasis, potentially reflecting broader alterations in lipid metabolism occurring during renal disease.49 We failed to document any association between plasma tChol concentration and lipiduria. However, plasma tChol concentration was not measured in all animals, and triglyceride concentration, considered a more relevant indicator of hyperlipidemia in dogs, was not evaluated. In addition, only a small number of breeds classically predisposed to dyslipidemia were represented in the study. These factors might have limited our ability to detect a true association.43

We did not identify an increased prevalence of overweight animals among lipiduric dogs or cats. These findings differ from those of a recent canine study reporting a higher proportion of obese dogs among individuals with CaOx urolithiasis, although BCS was not retained in multivariable analysis.43 However, the relationship between overweight status and urolith risk remains inconsistent across canine studies.50,51 The use of a 5-point BCS scale in the present study might have limited the precision of adiposity assessment compared with the 9-point system, which is considered more sensitive for estimating body fat percentage.52

This study has several limitations, mainly related to its retrospective design. First, no healthy control group was included, and the study sample encompassed heterogeneous disease categories, which might limit generalizability. Second, assessment of lipiduria relied exclusively on conventional urine sediment microscopy. However, lipid droplets are generally readily recognizable in urine under standard microscopy.2 Additionally, dietary history was not recorded, precluding assessment of any potential association between a high-fat diet and lipiduria. Finally, the interval between urine collection and sediment examination represents an additional important limitation, as storage conditions can alter urinary findings, particularly crystal formation. While storage for up to 24 hours appears to have minimal impact on struvite crystalluria, it might promote calcium oxalate crystal formation.53 In the present study, significant differences were observed only for struvite crystalluria in dogs, which is less influenced by storage conditions. Regarding lipid stability, available data in human medicine suggest that storage duration and conditions have minimal effects on urinary lipid profiles.54 It has also been suggested that lipiduria in cats might result from lipid contamination secondary to needle passage through body wall fat during percutaneous cystocentesis. Nevertheless, adipocytes derived from subcutaneous tissue are cytologically distinct from the lipid droplets observed on urinalysis.9

Lipiduria was a common finding in dogs and cats in the present study, particularly in cats. Although definitive conclusions cannot be drawn given the study limitations, our results suggest that age influences the frequency, but not the severity, of lipiduria in cats, without evidence of a sex predisposition. Concerning dogs, females were overrepresented among lipiduric individuals, and a possible association with struvite crystalluria was observed.

Supplementary Material

Supplementary_Materials_1_aalag232
supplementary_materials_1_aalag232.docx (21.6KB, docx)
Supplementary_Materials_2_aalag232
supplementary_materials_2_aalag232.docx (51.7KB, docx)

Abbreviations

AUS

abdominal ultrasonography

BCS

body condition score

CaOx

calcium oxalate

CKD

chronic kidney disease

pCreat

plasma creatinine

tChol

total cholesterol

USG

urine specific gravity

Appendix

Detailed description of the materials and methods

Urinalysis

Complete urinalysis included the USG measured by refractometry, the urine dipstick analysis performed using a 10-patch dipstick Multistix10SG® (Siemens), and microscopic examination of urine sediment. When available, quantitative bacterial culture results were also recorded. Proteinuria was only assessed by urine dipstick analysis, while hematuria and pyuria were considered only if confirmed at urine sediment examination.

In-house urinalysis (both USG and urine dipstick analysis) was performed shortly after sampling (<15 minutes), by visual assessment. Urine samples for cytological evaluation were collected in sterile tubes, stored at 4 °C for up to 8 hours, and subsequently shipped to an external laboratory at room temperature within 24 hours.

Microscopic examination of urine sediment was performed by conventional light microscopy, after centrifugation of urine at 1500 rpm for approximately 5 minutes in a conical tube. Urine microscopy was performed directly on wet preparations (before and after centrifugation) and on a stained air-dried smear (after centrifugation). The air-dried slides were stained with May-Grunwald-Giemsa stain. For direct sediment examination after centrifugation, the sediment was gently resuspended after removing the supernatant, then a drop of re-suspended sediment was pipetted on a glass slide and covered by a coverslip. For direct examination, urine was screened at 10× and 40×. The average number of erythrocytes, leukocytes, epithelial cells, crystals, casts, lipids (Table A1), and bacteria per high-power field was estimated semi-quantitatively.

Table A1.

Semi-quantitative ordinal categories used for routine assessment of lipiduria severity.

Category Score
Absent 0
Fair 0.5
Mild 1
Intermediate 1.5
Frequent 2
Very frequent 2.5
Severe 3
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Footnotes

2

Medistica. pvalue.io, a Graphic User Interface to the R statistical analysis software for scientific medical publications. 2019-2024. Available on: https://www.pvalue.io

Contributor Information

Mario Cervone, Clinique Vétérinaire Sevetys Crozatier, Paris 75012, France.

Damien Legroux, ANTECH Laboratories, Massy, Essonne 91300, France; Laboratoire de biologie médicale, Université de Lyon, VetAgro Sup, Campus Vétérinaire de Lyon, Marcy L'Etoile, France.

Gaelle Barral, Laboratoire de biologie médicale, Université de Lyon, VetAgro Sup, Campus Vétérinaire de Lyon, Marcy L'Etoile, France.

Eve Ramery, Laboratoire de biologie médicale, Université de Lyon, VetAgro Sup, Campus Vétérinaire de Lyon, Marcy L'Etoile, France; VetCyt, route de la Croix du Ban, Pollionnay, Essonne 91300, France.

Author contributions

Mario Cervone (Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing—original draft), Damien Legroux (Investigation, Writing—review & editing), Gaelle Barral (Investigation), and Eve Ramery (Investigation, Supervision, Writing—review & editing)

Conflicts of interest

Authors declare no conflicts of interest.

Funding

Authors received no specific funding for this work.

Off-label antimicrobial declaration

Authors declare no off-label use of antimicrobials.

Institutional animal care and use committee or other approval declaration

Authors declare no institutional animal care and use committee or other approval was needed.

Human ethics approval declaration

Authors declare human ethics approval was not needed.

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Associated Data

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Supplementary Materials

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Supplementary_Materials_2_aalag232
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