Simple blood and urine tests are available to diagnose most cases of kidney dysfunction. The common blood tests are a complete blood count (CBC) and a serum biochemical profile. Dogs with kidney disease have elevated levels of blood urea nitrogen (BUN), creatinine, phosphorus, potassium and other electrolytes, caused by the kidneys’ progressively deteriorating ability to filter waste products from blood and excrete them in urine.
The other main diagnostic tool for renal disease is a urinalysis. Veterinarians have chemical reagent test strips, instruments and other tools to help them evaluate a dog’s urine. Urine can be sampled by the “free catch” method (caught mid-stream to reduce contamination), by urinary catheterization or by a technique called cystocentesis. Cystocentesis involves puncturing the abdominal and bladder walls with a sterile needle and aspirating an uncontaminated urine sample into a syringe. The sample is assessed for color, odor, viscosity/turbidity/cloudiness and the presence of blood, casts, stones, crystals, protein, bacteria, glucose and other sediments and substances.
The veterinarian will also determine the urine’s specific gravity. “Specific gravity” is the weight of a substance compared with the weight of an equal amount of some other substance taken as a standard. For liquids, the standard is water. One of the key functions of healthy kidneys is to concentrate urine by filtering circulating waste products into it. Normal canine urine has a specific weight when compared with an equal amount of water. Urine that is abnormally dilute (low specific gravity) is highly suggestive of kidney disease.
Many veterinarians recommend an abdominal ultrasound to visualize the physical structure of the kidneys. This can help determine whether one or both kidneys are affected and can identify masses or other anatomical abnormalities. Abdominal radiographs (X-rays) may be taken to identify kidney enlargement (renomegaly). An electrocardiogram (ECG) can be used to assess heart function, which often is adversely affected by the elevated blood potassium levels that accompany renal disease. Specific tests for ethylene glycol are available for cases of suspected antifreeze toxicity; tests are available to detect leptospirosis and lyme disease, as well. Urine culture and sensitivity are highly recommended in dogs with chronic kidney disease, as they can help identify asymptomatic urinary tract infections which commonly occur in these patients. The urine protein-to-creatinine ratio, and the glomerular filtration rate, can both be measured. Finally, biopsies can be taken of one or both kidneys, either by surgical exploration or with the guidance of ultrasonography. Biopsies are extremely valuable to guide treatment decisions and disclose the extent of kidney damage.
Genetic screening tests for predisposition to familial kidney disease are reportedly under development for the Lhasa Apso, Shih Tzu and Soft-Coated Wheaten Terrier.