Page 1194 - Clinical Small Animal Internal Medicine

1132 Section 10 Renal and Genitourinary Disease

urine stasis, high rate of urinary excretion of drugs that
VetBooks.ir are poorly soluble in urine, and/or prolonged treat­
ment with high doses of potentially lithogenic drugs.

Urolith Diagnosis

Urinalysis
Urine Sediment
Urolithiasis typically induces inflammatory urine sedi­
ment, such as pyuria (presence of white blood cells),
hematuria (red blood cells), and proteinuria. Bacteria may
also be present if there is a primary or secondary UTI,
(i.e., infection induced by urolith‐associated trauma).
Figure 123.8 Suture‐induced stone (60% struvite, 40% calcium
phosphate) removed from a 4‐year‐old female spayed miniature Urine pH
schnauzer. Source: Courtesy of Andrew Moore, Canadian The urine pH of dogs and cats depends on many factors
Veterinary Urolith Centre. and can be affected by method of measurement. A study
in dogs found that urine dipstick tended to overestimate
Potassium magnesium pyrophosphate: the etiology of
● pH, in some cases yielding an alkaline result for a sample
these uroliths is not definitively known, and it is theo­ that had a mildly acidic urine as determined by the refer­
rized that formation is related to a type of temporary ence method. As such, if accurate measurement of urine
or permanent enzymatic dysfunction causing pyroph­ pH is important, a pH meter should be used. Relatively
osphate supersaturation of the urine. inexpensive hand‐held instruments are commercially
Melamine and/or cyanuric acid‐induced uroliths: after
● available.
a devastating occurrence of diet‐related renal failure in Certain minerals are more soluble in acidic or alkaline
dogs and cats, melamine urolithiasis or crystalluria pH. For these reasons, some minerals tend to precipitate
was noted in affected patients (Figure 123.9). and form stones in acidic (e.g., cystine, purine, calcium
Drug and drug metabolite uroliths: these are most
● oxalate) or in alkaline pH (e.g., struvite, calcium carbon­
commonly related to the use of the sulfonamides or ate, and calcium phosphate stones). At present, research
allopurinol and there are reports of fluoroquinolone indicates conflicting results regarding the role urine pH
(ciprofloxacin), primadone, and tetracycline uroliths. plays in the formation of calcium oxalate stones.
Factors predisposing to precipitation of drugs in urine
include reduced volume of highly concentrated urine, Crystals
Crystals may indicate the presence of uroliths or be nor­
mal, that is, no urolith. As such, specific therapy for crystal­
luria is not indicated unless a urolith is documented
through imaging, the patient has a history of urolithiasis or
urethral plugs (cats), and/or specific crystal types are noted.
In order to correctly identify crystalluria, urine should
be analyzed within one hour of collection. This is advised
because both calcium oxalate and struvite crystals can
form in vitro if there is a delay prior to analysis or due to
refrigeration. Crystal types that are not normally present
in the urine, and demand attention regardless of urolith
presence, include cystine, xanthine, and urate (excluding
Dalmatians).

Urine Culture
Urine culture and susceptibility should be performed in
Figure 123.9 Melamine cyanuric acid removed from the bladder
of a Burmese cat. Source: Courtesy of Andrew Moore, Canadian all patients with urolithiasis in order to detect infections
Veterinary Urolith Centre. and start appropriate antibiotic treatment if necessary,