The American Association of Veterinary Laboratory Diagnosticians issued the following protocol April 17.
If possible, serum and urine should be taken antemortem for a chemical analysis and urinalysis, including sediment examination. Typical crystals should be birefringent with polarized light. Information regarding the pet food involved—such as brand, lot number, and UPC—should be recorded. Samples of all food should be held by the client, the attending veterinarian, or the diagnostic laboratory.
A standard necropsy should be performed, using the judgment of the pathologist/veterinarian in charge, with particular attention paid to the urinary system. Photographs of pertinent lesions are recommended.
Samples of all important organs should be preserved in fixative. Lung, heart, liver, spleen, kidney, urinary bladder, adrenal gland, pancreas, thyroid/parathyroid, ileum, and brain are suggested, but others may be needed, depending on the lesions observed. Sections should be no thicker than 4 mm and fixed at fixative:tissue ratio of 10:1. In addition, samples of kidney, liver, fat, and urine should be taken, frozen, and held for future testing when a specific toxicologic assay is developed (as much tissue as is practical should be frozen and saved). If possible, sections of kidney should also be preserved in 100 percent (absolute) ethanol and/or snap-frozen in OCT medium to preserve crystals that might be washed away by prolonged formalin fixation.
All fixed tissues should be processed and embedded in paraffin within one to two days of fixation to best preserve crystal integrity. Routine H&E stains appear adequate to demonstrate crystals and renal tubular lesions, though Gomori's silver stain or polarized light may be used to highlight the crystals. Crystals can be viewed with or without staining on frozen or fixed sections.
Testing for other possible causes or contributing diseases should also be pursued, as a substantial proportion of the cases appear to be multifactorial. Examples include parvoviral enteritis, chronic tubulointerstitial disease, lymphosarcoma, or ethylene glycol toxicosis.
Questions or comments may be directed to Dr. Dalen W. Agnew, Diagnostic Center for Population and Animal Health, Michigan State University, 4125 Beaumont Road, Lansing, MI 48910-8104; phone, (517) 432-5806; firstname.lastname@example.org.