Comparative Imagery

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72.......................................................................................................................................................................NAVC Clinicians Brief / January 2010 / Comparative Imagery

Urine Crystals inDogs & Cats

Susan E. Fielder, DVM, MS, Diplomate ACVP,

Texas Veterinary Medical Diagnostic Laboratories, &

Theresa E. Rizzi, DVM, Diplomate ACVP, Oklahoma State University

Microscopic examination of urine sediment should be included aspart of a complete urinalysis. Crystalluria is not typically of clinicalsignificance and is often not associated with urolithiasis; however,

the presence of abnormal crystals or large numbers of common crystals mayindicate disease.

Metabolism, diet, underlying disease, sample collection, sample storage, andiatrogenic causes (eg, drug or IV contrast agent administration) may con-tribute to crystalluria. Crystal formation is often dependent on urine pH,osmolality, and temperature, as well as concentration and solubility of the

crystal-forming material. Identification of urine crystals is typically basedon their shape and color.

Match each of the pictures provided to one of the urine sediment find-

ings listed below. Each finding corresponds with only 1 picture.

See pages 74-75 for answers.

C o m p a r a t i v e I m a g e r y U R O L O G Y

___ AMMONIUM BIURATE

CRYSTALS

___ BILIRUBIN CRYSTALS

___ CALCIUM OXALATE

DIHYDRATE CRYSTALS

___ CALCIUM OXALATE

MONOHYDRATE CRYSTALS

___ CYSTINE CRYSTALS

___ HEMOGLOBIN PRECIPITATES

___ MELAMINE CYANURATE

CRYSTALS

___ TALC GRANULES

___ STRUVITE CRYSTALS

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Comparative Imagery / NAVC Clinicians Brief / January 2010.......................................................................................................................................................................73

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C o m p a r a t i v e I m a g e r y C O N T I N U E D

Ammonium biurate crystalsappear as yellow to brown spherules with irregular projections(thorn apple or sarcoptic mange appearance). A smooth, spheroid form may also be seen.Crystals typically form as a result of liver disease or portal vascular anomalies. Decreased con-version of ammonia to urea results in hyperammonemia, and increased concentration of ammo-nia in the urine leads to crystal formation. These crystals may also be seen in animals withammonium biurate urolithiasis. In general, they should be considered a pathologic crystal indica-tive of underlying hepatic disease; however, they may be seen in low numbers in clinicallynormal dalmatians and English bulldogs.

Struvite (magnesium ammonium phosphate) crystalsare often found in the urine of nor-mal dogs and occasionally in the urine of normal cats. The crystals typically appear as variablysized, colorless, rectangular (casket cover appearance) prisms (A). Struvite crystals can alsoform large, flat, square prisms or, uncommonly, X-shaped crystals (B). Struvite crystals usuallyform in alkaline urine, urine stored in the refrigerator, or urine left in an uncovered container atroom temperature. They may be present in animals with uroliths or urinary tract infection(caused by urease-producing bacteria, which convert urea to ammonium). In cats, struvite crys-talluria can occur in the absence of infection, likely due to ammonia excretion by the renaltubules.

Calcium oxalate monohydrate crystalsoccur as colorless, flat, elongated crystals withpointed ends, which give them a picket

fence appearance, or as spindle- or dumb-bell-shaped crystals. The latter 2 shapes canalso be formed by other calcium-containingcrystals, such as calcium carbonate (notobserved in dogs and cats). Calcium oxalatemonohydrate crystalluria can be observedwith acute ethylene glycol (antifreeze) toxic-ity; however, by the time animals present withclinical signs of acute renal failure, the crystalsmay no longer be detectable in the urine.

Melamine cyanurate crystalsare small, yel-low to brown spheres with centrally radiating

lines. These crystals have been associated withmelamine- and cyanuric acid-tainted food.Although their morphology is similar to spher-ical calcium carbonate crystals and the spheri-cal form of trimethoprim-sulfa crystals, theyare significantly smaller in size.

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Cystine crystalsare flat, hexagonal, colorless,variably-sized crystals that are often observedstacked together. These crystals are uncommon indogs and rarely found in cats. Cystinuria is due to

an inherited metabolic disorder involving defec-tive amino acid transport across renal tubularcells, which causes a selective increase in renalclearance and urinary excretion of cystine. Thecrystals form due to high concentration ofexcreted cystine and decreased solubility in acidicurine. Not all dogs with cystinuria will form cys-tine crystals, but if observed, the crystals arediagnostic for cystinuria. Dogs with cystinuria areat risk for developing cystine uroliths. In cats, cys-tine crystals may be confused with some forms ofstruvite crystals that are flat and 6- to 8-sided.

ilirubin crystalsappear as groups of goldenpicules. They may be seen in highly concen-rated urine from normal dogs, especially

males. When present in high numbers innconcentrated urine or in cats, these crystalsuggest an abnormality in bilirubin metabo-sm due to either hemolysis or cholestatic dis-ase (hepatic or posthepatic).

alcium oxalate dihydrate crystalsappears colorless squares with intersecting diagonalnes (envelope or Maltese cross appear-nce). They often occur in acidic urine or in

rine that has been stored either at room tem-erature or in the refrigerator. Calcium oxalateihydrate crystalluria is seen in animals withnhanced urinary oxalate excretion after

ngestion of oxalate-rich plants or plant-basedoods, those with enhanced urinary calciumxcretion due to hyperadrenocorticism orypercalcemia, those treated with urinarycidifiers, and those with certain urinary tract

nfections or uroliths. They can also be seen ininically normal animals.

Hemoglobin precipitatesappear as small,yellow to brown, variably sized, round topolygonal, refractile particles that resemblecrystalline material. Hemoglobin precipitates

can be present when there is overwhelmingintravascular hemolysis (eg, zinc toxicosis).This is an uncommon finding, even in dogswith intravascular hemolysis, and shouldalways be interpreted in light of other clinicalfindings. Amorphous phosphates and amor-phous urates have a similar appearance andare encountered commonly.These typicallyhave no significance.

Talc granulesmay be observed when pow-dered gloves are used to handle the sample.

They are variably sized, round with irregularborders, and often contain central cruciformlines. Talc granules, glass chips, and plantpollen are common crystal-like contaminantsof urine samples, and may be mistaken forurine crystals.

Comparative Imagery / NAVC Clinicians Brief / January 2010.......................................................................................................................................................................75

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