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in Journal of the American Veterinary Medical Association

  • Recognition of the diverse shapes of various urine crystals is necessary for their accurate identification.

  • Calcium oxalate dihydrate crystals most commonly have an octahedral or envelope shape.

  • Calcium ions and oxalic acid may form calcium oxalate crystals in urine.

  • Calcium oxalate dihydrate crystalluria is a risk factor for urolith formation.

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine effects of storage temperature and time on pH and specific gravity of and number and size of crystals in urine samples from dogs and cats.

Design—Randomized complete block design.

Animals—31 dogs and 8 cats.

Procedure—Aliquots of each urine sample were analyzed within 60 minutes of collection or after storage at room or refrigeration temperatures (20 vs 6°C [68 vs 43°F]) for 6 or 24 hours.

Results—Crystals formed in samples from 11 of 39 (28%) animals. Calcium oxalate (CaOx) crystals formed in vitro in samples from 1 cat and 8 dogs. Magnesium ammonium phosphate (MAP) crystals formed in vitro in samples from 2 dogs. Compared with aliquots stored at room temperature, refrigeration increased the number and size of crystals that formed in vitro; however, the increase in number and size of MAP crystals in stored urine samples was not significant. Increased storage time and decreased storage temperature were associated with a significant increase in number of CaOx crystals formed. Greater numbers of crystals formed in urine aliquots stored for 24 hours than in aliquots stored for 6 hours. Storage time and temperature did not have a significant effect on pH or specific gravity.

Conclusions and Clinical Relevance—Urine samples should be analyzed within 60 minutes of collection to minimize temperature- and time-dependent effects on in vitro crystal formation. Presence of crystals observed in stored samples should be validated by reevaluation of fresh urine. (J Am Vet Med Assoc 2003;222:176–179)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To identify demographic or signalment factors associated with calcium carbonate urolith formation in goats.

Design—Retrospective case series and case-control study.

Animals—354 goats with calcium carbonate uroliths (case animals) and 16,366 goats without urinary tract disease (control animals).

Procedures—Medical records of the Minnesota Urolith Center were reviewed to identify case goats for which samples were submitted between January 1, 1984, and December 31, 2012. Control goats evaluated at US veterinary teaching hospitals in the same time period were identified by searching Veterinary Medical Database records. Age, breed, sex, reproductive status, geographic location, season, and anatomic location of collected uroliths were analyzed to identify risk or protective factors associated with calcium carbonate urolithiasis.

Results—Nigerian dwarf goats had higher odds of developing calcium carbonate uroliths than did Pygmy goats (reference group). Several breeds had lower odds of this finding, compared with Pygmy goats; odds were lowest for mixed, Anglo-Nubian, and Toggenburg breeds. Breeds of African origin (Pygmy, Nigerian Dwarf, and Boer) comprised 146 of 275 (53%) case goats with data available. Goats of African descent had a higher risk of developing calcium carbonate uroliths than did goats of non-African descent (reference group). Males and neutered goats had higher odds of calcium carbonate urolithiasis, compared with females and sexually intact goats, respectively. Age category, geographic location, and season were associated with detection of calcium carbonate uroliths.

Conclusions and Clinical Relevance—Goats with calcium carbonate uroliths were typically neutered males, > 1 year of age, and of African descent. This study identified factors associated with calcium carbonate urolithiasis in goats; however, these associations do not allow conclusions regarding cause-and-effect relationships.

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine frequency of and interval until recurrence after initial ammonium urate, calcium oxalate, and struvite uroliths in cats and whether breed, age, or sex was associated with increased risk for urolith recurrence.

Design—Case-control study.

Animals—4,435 cats with recurrent uroliths.

Procedures—To identify recurrence of uroliths in cats for which uroliths were submitted for analysis at the Minnesota Urolith Center in 1998, the facility's database was searched for urolith resubmissions from the same cats between 1998 and 2003. Risk factors and differences in mean interval until recurrence were assessed.

Results—Of 221 cats with ammonium urate uroliths in 1998, 29 (13.1%) had a first and 9 (4.1%) had a second recurrence. Mean interval until recurrence was 22 and 43 months for the first and second recurrence, respectively. Of 2,393 cats with calcium oxalate uroliths in 1998, 169 (7.1%) had a first, 15 (0.6%) had a second, and 2 (0.1%) had a third recurrence. Mean interval until recurrence was 25, 38, and 48 months for the first, second, and third recurrence, respectively. Of 1,821 cats with struvite uroliths in 1998, 49 (2.7%) had a first and 3 (0.2%) had a second recurrence. Mean interval until recurrence was 29 months for first and 40 months for second recurrences.

Conclusions and Clinical Relevance—These results provided insights into the frequency of urolith recurrence in cats. Because some uroliths associated with recurrent episodes probably were not submitted to our facility, our data likely represented an underestimation of the actual recurrence rate.

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine whether storage in neutral-buffered 10% formalin in vitro has any effect on the composition of biogenic minerals of canine and feline uroliths.

Design—Prospective in vitro study.

Sample Population—Canine and feline uroliths submitted to the Minnesota Urolith Center from 34 dogs and 27 cats.

Procedures—Submissions from each dog or cat consisted of multiple uroliths of a single mineral type. After retrieval from the urinary tract, none of the uroliths had been placed in a preservative before submission. Evaluated uroliths were exclusively composed of the following: only struvite (uroliths from 5 dogs and 5 cats), calcium oxalate (5 dogs and 5 cats), calcium phosphate apatite (5 dogs and 5 cats), cystine (5 dogs and 5 cats), ammonium urate (5 dogs and 5 cats), or silica (5 dogs). One urolith from each dog or cat was quantitatively analyzed by polarized light microscopy, infrared spectroscopy, or both. Another urolith from the same animal was immersed in 1 mL of neutral-buffered 10% formalin for 48 hours at room temperature (22.5°C). Uroliths exposed to formalin were then air-dried for 30 minutes, and the analysis was repeated.

Results—After exposure to formalin, a portion of every struvite urolith was transformed into newberyite. This was not observed with any other urolith mineral type. Quantitative mineral analysis of nonstruvite uroliths revealed no detectable change in mineral composition. However, 3 of 10 ammonium urate uroliths dissolved when placed in formalin.

Conclusions and Clinical Relevance—To avoid misdiagnosis of mineral composition, uroliths should not be immersed in formalin prior to analysis.

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective

To determine whether morphology of single-mineral urocystoliths and age, sex, or breed data could be applied to facilitate radiographic and clinical urocystolith mineral type prediction, respectively, in dogs.

Sample Population

Database of 2,041 dogs with pure mineral composition urocystoliths.

Procedure

All uroliths were characterized according to geologic descriptive terminology and by breed, sex, and age of dog at time of sample submission. Summary statistics were used to compare features with specific mineral types. Observed trends were analyzed for statistical relevance between observed and expected frequencies for age, sex, color, size, shape, and surface, using the null hypothesis that differences by urocystolith mineral type did not exist. On the basis of expected breed occurrence derived by equations, the null hypothesis that urocystolith occurrence paralleled canine breed popularity was tested.

Results

Urocystoliths > 10 mm in any dimension were > 92% likely to be magnesium ammonium phosphate hexahydrate (MAP). Smooth, blunt-edged or faceted, and pyramidal urocystoliths were usually MAP. Jackstone shapes were almost always silica. Botryoidal (grape-like clusters) urocystoliths were likely to be oxalates. Breeds with high relative likelihood of urocystoliths included: English Bulldog, Pekingese, Pug, Welsh Corgi, and West Highland White Terrier. Breeds with low relative likelihood of urocystolith production included: German Shepherd Dog, Shar-Pei, and German Shorthaired Pointer. About 94% of urocystoliths produced in females or spayed females were MAP, whereas males and neutered males produced a greater assortment.

Conclusions and Clinical Relevance

For pure mineral composition urocystoliths, trends in mineral type among breeds and between sexes can be exploited clinically in the diagnosis and management of urolith-related disease. Size and shape, used in conjunction with age, breed, and sex, can facilitate pure urocystolith mineral type prediction. (Am J Vet Res 1998;59:379–387)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To evaluate the reliability of taurine concentrations measured in a single urine sample obtained from dogs 8 hours after eating, compared with taurine concentrations measured in 24-hour urine samples.

Animals

18 healthy Beagles.

Procedure

After emptying the urinary bladder by transurethral catheterization, dogs were fed a canned maintenance diet. Approximately 8 hours later, urine, plasma, and serum samples were obtained for determination of fractional urinary excretion of taurine and urine taurine-to-creatinine concentration ratios (Utaur:Ucr). Results were compared with 24-hour urinary taurine excretion rate.

Results

Unbound and total fractional urinary taurine excretion correlated well with unbound and total 24- hour urinary taurine excretion. However, bound fractional urinary taurine excretion correlated poorly with bound 24-hour urinary taurine excretion. Unbound and total Utaur:Ucr correlated well with unbound and total 24-hour urinary taurine excretion. However, bound Utaur:Ucr correlated poorly with bound 24-hour urinary taurine excretion.

Conclusion and Clinical Relevance

Fractional urinary excretion of unbound and total taurine, and unbound and total Utaur:Ucr are reliable indicators of 24-hour urinary unbound and total taurine excretion in healthy dogs. However, determination of 24-hour urinary taurine excretion is recommended for evaluating urinary bound taurine concentrations of dogs. (Am J Vet Res 1999;60:186–189)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To evaluate the effects of dilution on Stability of xanthine in canine urine stored at −20 C, and to evaluate the effects of storage at −20 C on Stability of xanthine in canine plasma.

Animals

6 reproductively intact female Beagles, 3.9 to 4.2 years old and weighing 8.5 to 10.1 kg.

Procedure

Dogs were fed a 31.4% protein (dry weight), meat-based diet for 21 days, and administered allopurinol (15 mg/kg of body weight, q 12 h) during days 14 to 21; urine and plasma samples were obtained on day 22, Urine samples were preserved undiluted or diluted, and divided into 1-ml aliquots for storage at −20 C for 1 to 12 weeks. Plasma samples were divided into 1-ml aliquots for storage at −20 C for 1 to 12 weeks. Urine and plasma xanthine concentrations were measured on day of collection (baseline) and after 1, 2, 4, 6, 9, and 12 weeks.

Results

Dilution of urine samples did not have a significant effect on consistency of xanthine concentration measured for up to 12 weeks of storage. Although xanthine concentration did not differ significantly between undiluted and diluted urine samples, average xanthine concentration measured in diluted samples was consistently higher, compared with that in undiluted samples. Compared with baseline values, plasma xanthine concentration was significantly lower at 6, 9, and 12 weeks of storage.

Conclusions

Measurement of xanthine concentration is reproducible in undiluted or diluted urine samples for up to 12 weeks, although dilution may provide better results. Measurement of plasma xanthine concentration is reproducible in samples stored for up to 4 weeks.

Clinical Relevance

To ensure reproducibility of measurements of xanthine concentration in urine samples collected from dogs that are affected with urate uroliths and receiving allopurinol, urine should be diluted 1:20 with deionized water. These measurements may be useful for monitoring dogs that are receiving allopurinol for dissolution or prevention of urate uroliths. (Am J Vet Res 1997;58:118–120)

Free access
in American Journal of Veterinary Research

Abstract

Objectives

To determine whether diet influences the metabolism of IV administered allopurinol in healthy dogs.

Animals

6 healthy female Beagles, 4.9 to 5.2 years old and weighing 9.6 to 11.5 kg.

Procedures

Allopurinol was administered IV (10 mg/kg) while dogs consumed a 10.4% protein (dry weight), casein-based diet or a 31.4% (dry weight), meat-based diet. After each dose, plasma samples were obtained at timed intervals, and concentrations of allopurinol and its active metabolite, oxypurinol, were determined by high-performance liquid chromatography. An iterative, nonlinear regression analytical program was used to determine the weighted leastsquares, best-fit curves for plasma allopurinol and oxypurinol concentration-time data. From these data, pharmacokinetic parameters were calculated.

Results

Pharmacokinetic parameters for allopurinol and oxypurinol were not different when comparing the effect of diet.

Conclusion

There is no influence of diet on pharmacokinetic parameters of allopurinol or oxypurinol.

Clinical Relevance

In contrast to observations in human beings, allopurinol metabolism is not influenced by diet. Therefore, formation of xanthine-containing calculi in dogs consuming a high-protein diet and receiving allopurinol is probably not attributable to alteration of allopurinol metabolism. (Am J Vet Res 1997;58:511–515)

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in American Journal of Veterinary Research