urinary crystals

8/7/2019 Urinary Crystals

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URINARY CRYSTALSby Geoffrey K. Dube and Robert S. Brown

A 26 year-old man presents with a fever andweakness. His WBC is 133,000, with 83% blasts.Creatinine is 2.0 mg/dl and serum uric acid is 15.4mg/dl.

2004, Beth Israel Deaconess Medical Center, Inc.


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A 26 year-old man presents with fever and a rash. His WBC is 133,000,

with 83% blasts. Creatinine is 2.0 mg/dl and serum uric acid is 15.4 mg/dl.

Assuming that this patient has uric acid crystalluria,which of the following might you find on urine

dipstick?a. Urine pH 5.0b. 4+ hemec. 4+ glucosed. 4+ protein


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Uric acid crystals invariably form in acidic urine,

typically with a urine pH < 5.5. Uric acid is soluble inalkaline urine, preventing the precipitation of uratecrystals. The inability of uric acid to crystallize aturine pH > 7.0 is the rationale for urinaryalkalinization in patients at risk for acute uric acidnephropathy. Uric acid crystalluria is not associatedwith significant amounts of hematuria, glycosuria or

proteinuria.


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Although crystals can be seen in certain clinicalscenarios, such as kidney stone disease or acutecrystal nephropathy, visualizing crystals under themicroscope does not guarantee that the crystals were

present in the urinary system. Crystals can continueto form after micturition. Crystal precipitation aftermicturition is most commonly due to changes intemperature, as can occur if the urine is stored atroom temperature or in a refrigerator, or changes in

urinary pH, as can occur in the presence of infectiondue to urea-splitting organisms.


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Assuming that this patient has uric acid crystals, whatwould you expect to see on microscopy?

a. Amber-colored rhomboid crystalsb. Colorless, hexagonal crystalsc. Colorless, "coffin-lid"-shaped crystalsd. Colorless, dumbbell-shaped crystalse. "Shocks of wheat"


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Uric acid crystals can vary in both size and shape, as can beseen in the slide above. They can look like barrels, rosettes,

rhomboids, needles or hexagonal plates. They are usuallyamber in color, irrespective of the size or shape of the individualcrystal. However, urate crystals may assume the color of anypigments (such as bilirubin or the medication pyridium) that arepresent in the urine. Urate crystals can occasionally be seen innormal subjects, although they are much more common in

patients with urate nephrolithiasis or acute urate nephropathy.


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The slide on the left shows a a uric acid crystal as viewed withlight microscopy. The slide on the right shows the same crystal

as viewed under polarized light. Uric acid crystals arebirefringent and beneath polarized light assume a polychromaticappearance. Their bright colors under polarized lightdistinguishes uric acid crystals from other types of crystals.


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In contrast to polymorphic urate crystals, cystine crystals aremonomorphic, colorless hexagonal plates which look similar to

benzene rings. The urine sediments from two patients withcystine crystals are shown above. Cystine crystals may beisolated or may be heaped upon one another. They occur in thesediment of patients with cystinuria, a genetic defect in renalcystine transport. They are found in acidic urine, typically with aurine pH < 6.0.


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Triple phosphate, or struvite, crystals are described

as having a "coffin-lid"-shaped appearance. Severalstruvite crystals are shown above. Struvite crystalsare composed of magnesium ammonium phosphate.They are typically seen in alkaline urine, with a urinepH > 7.0.


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Triple phosphate crystals are seen in patients with urinary tractinfections caused by urea-splitting bacteria, such as Proteus

mirabilis, and are frequently found in the urine of patients withinfected calculi (struvite stones). In addition to triple phosphatecrystals, microscopy in these patients with urinary tract infectionsmay show significant leukocyturia (arrows, above right) andbacteriuria.


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Calcium oxalate crystals are usually found in acidic urine. They mayoccur as either bihydrated or monohydrated calcium oxalate. Calciumoxalate bihydrate crystals appear as colorless bipyramids of varioussizes (envelope form, above left). Calcium oxalate monohydrate

crystals are colorless and can assume several shapes, includingovoids, biconcave disks, rods and dumbbells (above right, yellowarrows). They can be seen in normal individuals with high dietaryoxalate ingestion, in patients with nephrolithiasis, and in patients withacute renal failure due to ethylene glycol ingestion.Above right, reprinted with permission, Coe F.L. et al.. New Engl J Med 327:1141-1152.


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Urinary crystals can also be seen in patients taking certain medications.One example is sulfadiazine: these crystals appear as striated shells or"shocks of wheat. A sulfadiazine crystal is shown on the left. Othermedications that can cause urine crystals to form include indinavir,intravenous acyclovir, and triamterene. When these medications aregiven in high doses or to volume depleted patients, the crystals cancause acute renal failure by crystalline blockage of the renal tubules.An example of an indinavir crystal is shown on the right: the top panelshows rectangular plates of various sizes containing needle crystals,while the bottom panel shows indinavir crystals in a sheaf of numerous,densely packed needles.Indinavir crystals reprinted with permission, Gagnon, R. F. et. al. Ann Intern Med 1998;128:321

urinary crystals

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