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Introduction to Canine Urolithiasis 821

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Figure 38-4. Photomicrographs of common crystals found in urine sediment. Calcium oxalate monohydrate (dumbbell form, large arrow) and
calcium oxalate dihydrate (octahedral form, small arrows) (Top, Left). Calcium oxalate dihydrate; octahedral form (Top, Right). Magnesium
ammonium phosphate (struvite); prisms (Middle, Left). Cystine; flat, colorless hexagonal plates (Middle, Right). Ammonium urate; thorn apple
form (Bottom, Left). Amorphous xanthine; spheroids (Bottom, Right).

specimen preparation (e.g., centrifugation vs. noncentrifugation ture of crystals should be evaluated, as well as their tendency to
and volume of urine examined) and preservation. As men- aggregate.
tioned above, in vitro changes that occur after urine collection Urinary pH influences the formation and persistence of sev-
may enhance formation or dissolution of crystals. Although in eral types of crystals.Therefore, it is often useful to consider pH
vitro changes may be used to enhance detection of certain types when interpreting crystalluria (Table 38-3). Different crystals
of crystals (e.g., acidification to cause precipitation of cystine), tend to form and persist in certain urinary pH ranges, although
in vitro crystal formation may have no clinical relevance to in there are exceptions. Exceptions may be related to large con-
vivo formation of crystals in urine. When knowledge of in vivo centrations of lithogenic substances in urine or recent in vivo or
urine crystal type is especially important, fresh, warm speci- in vitro changes in urinary pH.
mens should be serially examined. The number, size and struc- Refrigeration is an excellent method to preserve many phys-