Crystalluria indicates that the urine is supersaturated with the compounds that comprise the crystals, e.g. ammonium, magnesium and phosphate for struvite. Crystals can be seen in the urine of clinically healthy animals or in animals with no evidence of urinary disease (such as obstruction and/or urolithiasis). However, some crystals can be pathologically relevant in certain circumstances (see example of ammonium biurate below). Note that crystals may not form in all urines supersaturated with these compounds. A number of in vivo and in vitro factors influence the types and numbers of urinary crystals in a given sample as indicated in the table below.
In vivo factors include:
- Concentration and solubility of crystallogenic substances contained in the specimen,
- Urine pH,
- Diet,
- Excretion of diagnostic imaging and therapeutic agents.
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In vitro factors include:
- Temperature (solubility decreases with temperature),
- Evaporation (increases solute concentration),
- Urine pH (changes with standing and bacterial overgrowth).
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Crystlas are subjectively quantified in urine as few, moderate and many. For crystals that are large, e.g. calcium carbonate and struvite, this assessment is made from low power (10x objective). For smaller crystals (e.g. amorphous, calcium oxalate dihydrate), the high power (40x objective) is used.
Source : © Cornell University |
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