Comparison of three techniques for the diagnosis of urinary tract infections in dogs with urolithiasis

OBJECTIVES: To identify an appropriate sampling technique(s) to accurately detect the bacteria causing urinary tract infections in dogs with urolithiasis. METHODS: Twenty-one dogs with urolithiasis were included in the study. Three types of samples were taken from each dog. Urine was collected by cystocentesis, and a urinary bladder mucosal biopsy and urolith were retrieved during cystotomy. The samples were then cultured on blood agar and MacConkey's agar to identify the bacteria associated with urinary tract infections. RESULTS: Bacterial urinary tract infection was found in 16 cases (76.19 per cent). The most prevalent bacteria found to cause urinary tract infection were Escherichia coli (n=7), followed by coagulase-positive Staphylococcus species (n=4), Klebsiella pneumoniae (n=2), Pseudomonas aeruginosa (n=2) and Proteus mirabilis (n=1). In the case of a positive urine culture, the same bacteria were also cultured from the urinary bladder mucosal biopsy alone or from both the urinary bladder mucosal biopsy and urolith. However, in the case of a negative urine culture, bacteria were found to be present in the urinary bladder mucosal biopsy or urolith cultures in 23.81 per cent of dogs. The uroliths that gave positive culture results were either infection-induced uroliths composed of struvite and calcium carbonate phosphate, ammonium acid urate only or metabolic uroliths composed of calcium oxalate and calcium phosphate, or calcium phosphate only. All the uroliths that gave negative culture results were metabolic uroliths composed of calcium oxalate and/or calcium phosphate, and uric acid and calcium phosphate. CLINICAL SIGNIFICANCE: When the culture from the urine obtained by cystocentesis is negative, cultures of urinary bladder mucosal biopsy and urolith are recommended in dogs with urolithiasis in order to accurately assess the microbiological status of the urinary tract.     

Etiopathogenesis of canine struvite urolithiasis

Urine must be oversaturated with magnesium ammonium phosphate for struvite uroliths to form. Oversaturation of urine with magnesium ammonium phosphate may be associated with several factors, including urinary tract infections with urease-producing microbes, alkaline urine, diet, and genetic predisposition. Of the urease-producing microbes, staphylococci are most struvitogenic in dogs. The precise mechanisms resulting in formation of sterile struvite uroliths in dogs have not been determined.     

Surgical removal of canine uroliths

Surgery is indicated for patients with obstructive uropathy; calcium oxalate, calcium phosphate, silica, and perhaps cystine uroliths; uroliths refractory to medical dissolution; nephrolithiasis and progressive renal dysfunction; anatomic defects predisposing to urinary tract infection; and problems precluding medical management. The goals of surgical management include removal of all uroliths while preserving organ function, eliminating partial or complete obstruction to urine outflow, and correction of anatomic abnormalities that predispose the patient to infection and or urolithiasis.     

Medical dissolution of feline struvite urocystoliths

The efficacy of a diet designed to facilitate dissolution of feline magnesium ammonium phosphate (struvite) uroliths was evaluated in 30 cases of urolithiasis, sterile struvite uroliths dissolved in a mean of 36 days after initiation of dietary treatment. In 5 cases of urolithiasis, struvite urocystoliths associated with urease-negative bacterial urinary tract infection dissolved in a mean of 23 days after initiation of dietary and antimicrobial treatment. In 3 cases of urolithiasis, struvite urocystoliths associated with urease-positive staphylococcal urinary tract infection dissolved in a mean of 79 days after initiation of dietary and antimicrobial treatment. Dissolution of uroliths in cats fed the treatment diet was associated with concomitant remission of dysuria, hematuria, and pyuria, and reduction in urine pH and struvite crystalluria. In one case, a urocystolith composed of 100% ammonium urate, and in another case, a urolith composed of 60% calcium phosphate, 20% calcium oxalate, and 20% magnesium ammonium phosphate did not dissolve.     

Nutrient intake and urine composition in calcium oxalate stone-forming dogs: comparison with healthy dogs and impact of dietary modification

Nutrient intake and urine composition were analyzed in calcium oxalate (CaOx)stone-forming and healthy control dogs to identify factors that contribute to CaOx urolithiasis. Stone-forming dogs had significantly lower intake of sodium, calcium, potassium, and phosphorus and significantly higher urinary calcium and oxalate concentrations, calcium excretion, and CaOx relative supersaturation (RSS). Feeding a diet used in the treatment of canine lower urinary tract disease for 1 month was associated with increased intake of moisture, sodium, and fat; reduced intake of potassium and calcium; and decreased urinary calcium and oxalate concentrations, calcium excretion, and CaOx RSS. No clinical signs of disease recurrence were observed in the stone-forming dogs when the diet was fed for an additional 11 months. The results suggest that hypercalciuria and hyperoxaluria contribute to the formation of CaOx uroliths in dogs and show that dietary modifications can alter this process.     

Associations between dry dietary factors and canine calcium oxalate uroliths

OBJECTIVE: To identify factors in dry diets associated with the occurrence of calcium oxalate (CaOx) uroliths in dogs. ANIMALS: 600 dogs with CaOx uroliths and 898 dogs without urinary tract diseases. PROCEDURE: Univariate and multivariate logistic regression were performed. RESULTS: Compared with diets with the highest concentrations of sodium, dry diets with the lowest concentrations of sodium, phosphorus, calcium, chloride, protein, magnesium, or potassium were linearly associated with increased risk of CaOx urolith formation. Significant nonlinear associations between increased occurrence of CaOx uroliths and urine acidifying potential and low moisture content were observed. Significant nonlinear associations between decreased occurrence of CaOx uroliths and carbohydrate and fiber contents were observed. A significant association between the occurrence of CaOx uroliths and dietary fat was not observed. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that dry diets formulated to contain high concentrations of protein, calcium, phosphorus, magnesium, sodium, potassium, and chloride may minimize formation of CaOx uroliths. In addition, comparison of risk and protective factors of various diet ingredients fed to dogs with CaOx uroliths suggests that although similar findings were observed in canned and dry formulations, in general, greater risk is associated with dry formulations. However, before these hypotheses about dietary modifications are adopted by food manufacturers, they must be investigated by use of appropriately designed clinical studies of dogs with CaOx urolithiasis.     

Etiopathogenesis, clinical manifestations, and management of canine calcium oxalate urolithiasis

Calcium oxalate uroliths are commonly called metabolic uroliths because they are sequelae of a variety of metabolic abnormalities that alter the composition of body fluids and urine. Factors incriminated in the etiopathogenesis of calcium oxalate urolithiasis include hypercalciuria, hyperoxaluria, and hyperuricosuria. The predominant type of calcium oxalate urolith encountered in dogs is the monohydrate form; however, the dihydrate form may also occur. Male dogs have been more frequently affected than female dogs. Medical therapy should be formulated with the goal of reducing urine concentration of calculogenic substances.     

Evaluation of urine and serum metabolites in miniature schnauzers with calcium oxalate urolithiasis.

To evaluate underlying causes of calcium oxalate urolithiasis, 24-hour excretion of urine metabolites was measured in 6 Miniature Schnauzers that formed calcium oxalate (CaOx) uroliths during periods when they were fed a standard diet and during periods when food was withheld. Serum concentrations of parathyroid hormone and 1,25-dihydroxyvitamin D also were evaluated. Serum calcium concentrations were normal in all 6 affected Miniature Schnauzers; however, during diet consumption, mean 24-hour urinary excretion of calcium was significantly (P = 0.025) higher than calcium excretion when food was withheld. In 1 dog, urinary calcium excretion was lower during the period of food consumption, compared with the period when food was withheld. Compared with clinically normal Beagles, Miniature Schnauzers that formed CaOx uroliths excreted significantly greater quantities of calcium when food was consumed (P = 0.0004) and when food was withheld (P = 0.001). Miniature Schnauzers that formed CaOx uroliths excreted significantly less oxalate than clinically normal Beagles during fed (P = 0.028) and nonfed (P = 0.004) conditions. Affected Miniature Schnauzers also excreted abnormally high quantities of uric acid. Excretion of citrate was not different between Miniature Schnauzers with CaOx urolithiasis and clinically normal Beagles. In 5 of 6 Miniature Schnauzers with CaOx urolithiasis, concentrations of serum parathyroid hormone were similar to values from age- and gender-matched Miniature Schnauzers without uroliths. The concentration of serum parathyroid hormone in 1 dog was greater than 4 times the mean concentration of clinically normal Miniature Schnauzers. Mean serum concentrations of 1,25-dihydroxyvitamin D in Miniature Schnauzers with calcium oxalate urolithiasis were similar to concentrations of clinically normal Miniature Schnauzers.     

Urolithiasis in finishing pigs

Urolithiasis in sows and neonatal pigs is well-known, but information on its occurrence and impact in finishing pigs is sparse. This study reports three outbreaks of urolithiasis in finishing pigs. In one herd, no symptoms were observed, whereas in the other herds the presence of calculi caused obstruction of the urinary tract resulting in death. Using infra-red spectroscopy, the predominant mineral-type found in the uroliths was calcium carbonate (calcite). Only small amounts of calcium oxalate (< 1%) could be detected. A high urinary pH, small abnormalities in the mineral composition of the feed and insufficient drinking water were the most important risk factors identified. To prevent urolithiasis, it is important to ensure adequate water intake, to provide a balanced mineral diet, and to avoid urinary tract infections.     

Medical management of male and female cats with nonobstructive lower urinary tract disease

This case is typical of recurrent urolithiasis managed by repeated surgery. Retrospective assessment of the disorder indicates the need for quantitative analyses of uroliths removed by cystotomy. Compliance of the owners with recommendations to minimize recurrent urolithiasis might have been beneficial. Results of medical therapy designed to induce dissolution of uroliths in this case are representative of preliminary findings of medical dissolution of naturally occurring struvite uroliths in ten other cats. It is of interest that the uroliths dissolved even though no effort was made to induce diuresis. The underlying cause of UTI in this patient may have been damage to the lower urinary tract induced by previous diagnostic and therapeutic procedures and/or sterile struvite uroliths that compromised local host defense mechanisms. Lack of urease production by the uropathogens suggests that they did not play a causative role in formation of uroliths. The need for preventative therapy of recurrent formation of uroliths after their medical dissolution is worthy of further comment. In this patient, specific measures to prevent urolith recurrence were not initiated because it is a part of a prospective clinical study. In the event uroliths recur, medical therapy designed to induce dissolution of uroliths would be repeated. Need for long-term preventative therapy would be dependent on the time interval between recurrent episodes (weeks, months, or years), and the effectiveness of medical therapy for urolith dissolution. Long-term prophylactic therapy would include urine acidifiers and diets low in magnesium.     

Levels of retinol and retinyl esters in plasma and urine of dogs with urolithiasis

Vitamin A (VA) deficiency and Tamm-Horsfall glycoprotein (THP), a protein that binds retinol and retinyl esters in canine urine, might be involved in the pathogenesis of urolithiasis in dogs. In the present study, we assessed levels of retinol, retinyl esters, retinol-binding protein (RBP) and THP in plasma and urine of dogs with a history of urolithiasis (n = 25) compared with clinically healthy controls (n = 18). Plasma retinol concentrations were higher in dogs with uroliths of struvit (P < 0.01), calcium oxalate (P < 0.05), urate (P < 0.01) and cysteine, but there were no differences in the concentrations of plasma RBP and retinyl esters. Excretion of urinary retinol and retinyl esters were tentatively, but not significantly higher in the stone-forming groups, which was accompanied by increased levels of urinary RBP (P < 0.01) and lower excretions in THP (P < 0.01). The results show that VA deficiency may be excluded as a potential cause for canine urolithiasis. However, the occurrence of RBP and a concomitant reduction of THP in urine indicates a disturbed kidney function as cause or consequence of stone formation in dogs.     

Canine and feline urolithiasis: Examination of over 50 000 urolith submissions to the Canadian Veterinary Urolith Centre from 1998 to 2008

This study reports on trends in canine and feline urolithiasis in Canada during the past 10 years. Age, sex, breed of animals and mineral composition from 40 637 canine and 11 353 feline bladder uroliths submitted to the Canadian Veterinary Urolith Centre between 1998 and 2008 were recorded. Struvite and calcium oxalate uroliths comprised > 85% of all uroliths submitted. In dogs, the number of struvite submissions has declined and the number of calcium oxalate submissions has increased. Struvite uroliths were most common in female dogs and calcium oxalate uroliths in male dogs. The shih tzu, miniature schnauzer, bichon frisé, lhasa apso, and Yorkshire terrier were the breeds most commonly affected for both struvite and calcium oxalate uroliths. Urate uroliths were most common in male dalmatians. In cats, struvite submissions declined and calcium oxalate submissions remained constant. Struvite and calcium oxalate uroliths were common in domestic, Himalayan, Persian, and Siamese cats. Urate uroliths were over-represented in Egyptian maus.     

Evaluation of the efficacy of a commercial diet in the dissolution of feline struvite bladder uroliths

Clinical signs of struvite urolithiasis resolved in an average of 19 days in cats fed either a canned or dry urine-acidifying, magnesium-restricted diet, and stones completely dissolved in 31 of 39 cats in an average of 30 days. Stones were surgically removed from five cats, and analysis revealed that these stones were not composed of struvite. The results of this study strongly suggest that the diet will dissolve naturally occurring feline struvite bladder uroliths.     

Evaluation of urinary and serum metabolites in Asian small-clawed otters (Aonyx cinerea) with calcium oxalate urolithiasis.

Baseline renal function data was collected during 24-hr periods of feeding and fasting from three male and three female adult Asian small-clawed otters (Aonyx cinerea) with calcium oxalate urolithiasis. Urine was analyzed for calcium, phosphorus, and oxalate, and urinalyses were performed. There was no evidence of glucosuria, which has been previously reported in Asian small-clawed otters with urolithiasis. Urinary oxalate levels were quite high when compared with those of dogs and humans without uroliths, and the ratio of urinary oxalate to calcium was close to 1:1 during periods of food consumption. There was no significant difference in urinary oxalate excretion between the fed and fasting states. Urinary calcium excretion was five times greater during feeding than during fasting. Calcium levels were higher in the otters than those reported for dogs without uroliths but were similar to those for normal humans. Water consumption and urine production were significantly higher during periods of food consumption. Serum chemistry analyses and electrolyte levels were also determined. There was no evidence of hypercalcemia. Fractional clearance of calcium and phosphorus and endogenous creatinine clearance were significantly higher during food consumption than during fasting. Parathyroid hormone levels were similar to those reported for dogs and cats. Serum 25-hydroxy-vitamin D was slightly lower in the otters than in dogs.     

Detection of occult urinary tract infections in dogs with diabetes mellitus

Dogs with diabetes mellitus may develop occult urinary tract infections. In this study, diabetic dogs with negative and positive bacterial urine cultures were compared. Records from 51 dogs with diabetes mellitus were reviewed at the University of Illinois. No difference was identified between the groups in urine specific gravity, pH, glucose, ketones, protein, red blood cells, white blood cells, or epithelial cells. Dogs with occult urinary tract infection did have an increased incidence of bacteriuria, but this was not a consistent finding. Therefore, the urine on all diabetic dogs should be cultured to accurately identify the presence or absence of bacterial urinary tract infections.     

Obstructive struvite ureterolithiasis in 4-month-old intact male Bernese mountain dog

A 4-month-old, 7 kg, intact male, Bernese mountain dog was presented for obstructive struvite ureterolithiasis. Multiple urethroliths, ureteroliths, and urocystoliths were present. Based on an abdominal ultrasound, there was severe left hydronephrosis and hydroureter from distal ureterolith obstruction, just proximal to the vesicoureteral junction. The dog was not azotemic. Successful treatment was accomplished via ventral cystotomy. Bladder wall culture revealed a methicillin-resistant Staphylococcus spp. No predisposing cause was identified. There are no known genetic predispositions in Bernese mountain dogs for struvite urolithiasis. The urinary tract infection resolved with surgical retrieval of the uroliths and antibiotic treatment. The dog remained clinically normal after the cystotomy but developed a subclinical urinary tract infection 4 mo post-operatively.Key clinical message:Urolithiasis is rare in pediatric veterinary patients. To the authors’ knowledge, this is the first report of obstructive ureterolithiasis in a puppy. There is no known genetic predisposition for urolithiasis in Bernese mountain dogs.     

Risk factors associated with feline urolithiasis

Urinary tract diseases are among the main reasons for consultation in veterinary clinics and hospitals. It affects animals of any age, breed and gender. Among the diseases that affect this system, urolithiasis is the second largest cause of clinical signs compatible with feline urinary tract disease. The term urolithiasis refers to the presence of uroliths in any region of the urinary tract, but it is more commonly seen in the bladder and urethra. Uroliths are classified based on the type of mineral present in their composition, therefore, quantitative and qualitative analyzes are important for a better therapeutic approach. The animals may suffer from the disease and be asymptomatic, or show nonspecific clinical signs, making the diagnosis difficult. The disease should not be seen as a single problem, but as a consequence of various disorders. As dietary, metabolic, genetic and infectious causes, as well as factors that potentiate the chance of development of uroliths such as breed, age, sex, age range, obesity, sedentary lifestyle, geographic region and climate. Thus, the knowledge of the factors that influence the formation of uroliths, as well as the understanding of the pathophysiology, are key elements for better alternatives of therapy and prevention. The recognition of these factors helps to identify susceptible populations, minimizing exposure and increasing the protection factors, which facilitates the diagnosis and treatment of patients with urolithiasis. The objective of this paper is to present the main risk factors involved in the formation of urinary lithiasis in felines.     

Prevalence of canine uroliths. Minnesota Urolith Center

Uroliths obtained from 839 dogs were evaluated by quantitative methods. Struvite was the most prevalent mineral detected; newberyite, calcium oxalate, calcium phosphate, uric acid, sodium and ammonium urate, cystine, and silica were detected much less frequently. Seven per cent of the uroliths had an identifiable nucleus and one or more surrounding layers of different mineral types. Although uroliths were found in all parts of the urinary tract, the urinary bladder was most common. Uroliths of different composition were encountered in a variety of breeds of both sexes and different ages.     

Treatment and prevention of feline struvite urolithiasis

A diet providing less than 20 mg of magnesium per 100 kcal that maintains urine pH near 6.0 3 to 5 hours after eating, or a diet providing this amount fo magnesium (see Table 2) with 1 gm of ammonium chloride or 1.5 gm of dl-methionine added daily, should be fed for 1 to 3 months to dissolve struvite uroliths (see Fig. 1). The low-magnesium diet should be fed indefinitely to prevent recurrence, because struvite urolithiasis and all of its effects (hematuria, pollakiuria, and/or complete to partial obstruction to urinary excretion) recurs repeatedly in cats that have previously experienced the condition if they are returned to regular cat food. In contrast, if a diet low in magnesium is fed, recurrence is uncommon. For cats that have never been affected, feeding a low-magnesium ration is unnecessary. For all cats, the following measures are recommended: encourage exercise, allow frequent urination, prevent obesity, decrease confinement, keep the litter box clean, and always have palatable water readily available.