Crystalluria
Crystalluria is defined as the presence of crystals in the urine. Calcium carbonate and calcium phosphate crystals are abundant in normal equine urine. These, along with mucus, impart a turbid, slightly opaque quality to normal equine urine (see Fig.
10.2). Herbivore urine is normally alkaline, which reduces the solubility of certain calcium- and phosphate-based compounds in urine, inducing crystal development. Therefore calcium phosphate, calcium carbonate, or calcium oxalate crystals may be present as an incidental finding in highly concentrated ruminant urine if the animal is healthy and free from signs of urinary tract disease. However, in male ruminants, heavy or persistent crystalluria may be a risk factor for urolithiasis because the combination of highly concentrated urine and urinary mineral precipitation is considered instrumental in calculogenesis. A precautionary review of diet, salt intake, and water management may be indicated in such cases.Crystalluria presents a medical problem when crystals enlarge through precipitation, causing microscopic or gross traumatic injury to the urinary epithelium and urinary tract obstruction. When crystals coalesce and enlarge to form calculi (uroliths), the calculi may remain occult or cause disease through trauma
■ BOX 10.4
■ BOX 10.5
Causes of Crystalluria in Horses and Ruminants
Alkaline urine
Calcium-based Crystalluria of horses (normal) Concentrated urine
Ethylene glycol intoxication
Oxalate intoxication
Urinary tract infection Urolithiasis
Vitamin C intoxication
to and obstruction of the urinary tract.20-22 As a result, the clinician usually detects Crystalluria in these animals during the diagnostic work-up for hematuria, dysuria, stranguria, pyuria, or signs of urinary tract obstruction. It is critical to note that the absence of crystalluria does not indicate that the urinary tract is free of calculi or renal mineralization, just as the presence of crystalluria does not necessarily indicate disease.23,24 Causes of crystalluria are listed in Box 10.4.
Approach to Diagnosis of Crystalluria
Toxins such as oxalic acid and ethylene glycol can induce calcium oxalate crystalluria, so access to oxalate-containing plants and storage areas or garages should be investigated.23,25 High doses of parenteral vitamin C can induce calcium oxalate deposition in the urinary tract, and there is also a suggestion that primary hyperoxaluria may be related to inherited metabolic defects.25,26 Previous urinary tract surgery, dystocia, or genital trauma may indirectly contribute to crystalluria, as abnormal structure of the urinary tract, suture material inadvertently placed in the tract, or loss of uroepithelial integrity can promote crystal precipitation into calculi.
The hairs surrounding the preputial orifice or vulva should be carefully examined for visible crystals that cling to the hair, indicating heavy crystalluria (see Fig. 10.3). In males, given that urolithiasis is an important diagnosis to investigate, urinary tract patency should be determined.
Crystalluria and calculus formation can be caused by UTI because urease-producing bacteria may increase the pH of urine to the point of inducing precipitation of certain minerals suspended in the urine into calculi.27 In addition, inflammatory exudation into the urinary tract provides nidi for deposition of urinary minerals.27