Urianalisis

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Quantitative analysis of urinary calculi
in dogs and cats

Introduction
Accurate identification of the type or types of minerals present in a urolith is paramount in order to apply the appropriate therapeutic and preventative regime. Uroliths may be collected by spontaneous voiding (use an aquariumfishnet to catch a urolith), voiding urohydropropulsion, aspiration into a urethral catheter, cystoscopy, or surgical removal (1,2,3). All uroliths retrieved should be quantitatively analyzed by specialized laboratories to determine mineral composition of any/all of the 4 layers that may be present (Figure 1). There are several techniques available for quantitative analysis including polarizing lightmicroscopy, infrared spectroscopy, scanning electron microscopy with x-ray microanalysis and x-ray diffraction. Each of these techniques will be discussed in this article. Centers offering quantitative analysis include; The Canadian Veterinary Urolith Centre, University of Guelph, The Minnesota Urolith Center, College of Veterinary Medicine, University of Minnesota, The Department of Urology,University of Bonn, Germany, Urinary Stone Analysis Laboratory, University of California at Davis and The Budapest Urolith Centre.

Andrew Moore, MSc
Canadian Veterinary Urolith Centre, University of Guelph, Lab Services, Guelph, Ontario, Canada Andrew Moore completed an MSc in Botany in 1990, and has been the supervisor of the Analytical Microscopy Lab, Laboratory Services, University of Guelphsince 1992. This facility identifies foreign materials in food products for industry and government and provides microscopy services to support disease diagnosis in veterinary and plant pathology. In 1998, he helped to establish the Canadian Veterinary Urolith Centre, which continues to provide quantitative urolith analysis to Canadian Veterinarians in partnership with Medi-Cal/ Royal Canin VeterinaryDiet.

22 / / Veterinary Focus / / Vol 17 No 1 / / 2007

Uroliths containing at least 70% of a single mineral are classified as that mineral type (4). Uroliths with nidus and shells of different mineral types are classified as compound (4). Uroliths containing < 70% of a single mineral component and without an obvious nidus or shell were classified as mixed (4). Historically, the compositionof calculi has been determined by visual examination, appearance on radiographs, inferred from the presence of certain crystals in the urine, and by the use of commercially available test kits. While the physical appearance of many calculi is a good indication of their composition (4,5), we have found that all of the different stone types can form in a wide variety of shapes, sizes and colors.Even technicians who have analyzed thousands of stones in our facility are sometimes fooled in their initial, visual evaluation of what they expect specific calculi to be. Most importantly, the external appearance of a calculus almost never gives an indication of the composition of the interior, the very center of which is the key to accurate diagnosis and treatment, and which may be quite differentfrom the bulk of the stone. For example, Figure 2 shows a large calculus from a 16 year old spayed female domestic short hair, which might be mistaken for a silica jackstone. Quantitative analysis showed the nidus to be 95% calcium oxalate monohydrate, 5% calcium phosphate, and the stone and shell to be composed of 100% calcium oxalate monohydrate. Figure 3 is a good illustration of the visualdifferences present among canine ammonium urate stones. Appearance on a radiograph is also not 100% reliable, both in terms of the shape of the individual calculi, and whether the stones are even visible. We recently analyzed a stone from a Shih Tzu that was primarily struvite (normally radiodense), yet was invisible on a standard radiograph. The stone was sufficiently soft and porous to prevent...