Introduction
Kidney disease in dogs is reliably diagnosed through blood and urine tests. In some cases, ultrasonography is also used to assess the extent of the disease.
Diagnosing Kidney Disease in Dogs
The clinical signs of both acute and chronic kidney disease are largely nonspecific and seem to appear in dogs suddenly, even though the damage may have been progressing for some time. Simple blood and urine tests are available to diagnose kidney dysfunction. The common blood tests are a complete blood count and a serum biochemical profile. Dogs with kidney damage have elevated blood levels of blood urea nitrogen (BUN), creatinine, phosphorus and potassium, caused by the kidneys’ progressively worsening ability to filter waste and other products from blood and excrete them in urine.
The other component of diagnosing renal disease is a urinalysis. Veterinarians have different test strips, instruments and other tools to help them assess the make-up of a dog’s urine sample. Urine can be taken by the “free catch” method or by a technique called cystocentesis.
Cystocentesis involves puncturing the bladder with a sterile needle, usually passed through the abdominal wall, and drawing an uncontaminated urine sample through a syringe. The veterinarian will then examine the urine to identify its “specific gravity” and determine whether protein is present in the sample. 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 waste products into it. Normal urine in dogs therefore has a certain normal weight. Abnormally dilute urine is highly suggestive of kidney abnormalities. Proteins can end up in the urine when damaged kidneys are unable to manage the balance of products normally filtered from blood. Urinalysis can also disclose the abnormal presence of stones or crystals.
Once kidney disease is diagnosed via blood and urine analysis, many veterinarians will recommend an ultrasound examination to look at the physical structure of the kidneys. This can be helpful to determining whether one or both kidneys are affected. Abdominal radiographs are often taken to identify kidney enlargement (renomegaly). Electrocardiograms can be used to assess heart function, which can be affected by elevated blood potassium levels seen in cases of renal disease. In cases of suspected antifreeze toxicity, ethylene glycol testing is available. Finally, renal biopsies can be taken and are very valuable prognostically.