Diagnosis Of, And Screening For, Kidney Failure In Cats
Up to 75% of a cat's kidney function can be lost before it shows any outward signs of ill health. Inside the body, it's a different story. Earlier stages of kidney failure cause changes in the composition of a cat’s blood and urine. These changes can be picked up with simple screening tests by a veterinarian. Screening tests are important, as it's vital to catch the problem quickly if your cat is to stand the best chance of a longer, healthier life.
Which screening and diagnostic tests should be carried out, and when?
Regular physical exam
Recommended for all cats over 7 years of age
A basic annual physical examination by a veterinarian is simple, quick, non-invasive and can be carried out at low cost. The exam also gives your veterinarian the best chance of diagnosing other conditions early, not just kidney failure. Cats of any age will benefit from an annual health check. But they are increasingly important in middle to old age, and are recommended for all cats over seven years of age.
A physical examination to check for early signs of kidney failure will ideally include:
- A weight check, as weight loss can be an early indicator of many diseases, including kidney failure.
- Blood pressure measurement, as high blood pressure is a common consequence of kidney failure in cats.
- An examination of the eyes to check for any damage caused by high blood pressure.
- A urine test. Cats normally produce concentrated urine (they evolved as desert-living creatures); diluted urine can be an early sign of kidney disease. Urine can be collected from your cat at home using non-absorbent litter from your veterinarian. Urine can also be collected via cystocentesis (where it’s sampled using a needle inserted into the bladder).
A general physical examination can also reveal problems like dehydration, anaemia, if the kidneys feel abnormal (e.g. enlarged due to polycystic kidney disease) or issues caused by other diseases.
If urine and blood pressure checks reveal nothing untoward, they are still a useful exercise. They help to establish normal readings for your cat, against which your veterinarian can compare the results of future tests.
Blood tests
Blood tests are recommended when a physical exam indicates the possibility of kidney failure.
When two-thirds to three-quarters of renal function is lost, the kidney is less effective at excreting waste products produced by the body. These waste products build up in the bloodstream, a condition known as azotaemia. Along with urine test results, veterinarians can confirm a diagnosis of kidney failure by analysing blood for increased levels of two waste products: urea and creatinine.
Azotaemia can be seen for reasons other than kidney failure, for example, dehydration or analysis of a blood sample collected within a few hours of eating a meal. These need to be eliminated as possible causes before a diagnosis of kidney failure is made.
Blood tests can be slightly more expensive than the tests carried out during a basic exam (such as urinalysis), but they are a routine and straightforward procedure. A small amount of blood is taken from the cat, and the sample is usually sent to a laboratory for analysis.
Advanced Diagnostics
In some cases, further tests may need to be carried out to pinpoint the cause of kidney failure. They include:
Renal Ultrasound
Ultrasound equipment is sometimes used to scan the kidney for problems such as polycystic kidney disease. This is a relatively straightforward and non-invasive procedure. However, ultrasound equipment is not available in all practices, so the procedure may require referral to a specialist veterinarian.
Renal Biopsy
Kidney biopsy is not required in most renal disease patients. It is a specialist procedure and is usually performed in patients where cancer (e.g. lymphoma) or other rare causes of renal disease (e.g. glomerulonephritis, amyloidosis) are suspected. The procedure involves taking a sample of suspect tissue from the kidney, under general anaesthetic, and sending it for laboratory analysis.