Tanya's Comprehensive Guide to Feline Chronic Kidney Disease

CKD is normally diagnosed via blood tests and urinalysis (urine tests).
Sometimes other tests may be appropriate, for example, if a kidney infection is suspected, or if a young cat has CKD.
The tests below are listed in order of invasiveness.

Occult Blood Test for Gastro-Intestinal Bleeding Back to Page Index

This test is the least invasive, because initially it does not require that you take your cat to the vet.

If you suspect that your cat has gastro-intestinal bleeding (which could be the case if your cat's BUN:creatinine ratio is high, PCV or HCT is falling and albumin and/or the MCV are low), you should take a stool sample to your vet for testing and ask for an occult blood test.

You can also buy the EZ Detect test from pharmacies, which tests for blood in the stool or urine (this is a human test but can also be used for cats).

I did this test when Ollie was anaemic. My vet had never been asked to do this test before, but Ollie's test was positive.

Do not give iron supplements for a couple of days before obtaining a sample for testing. Ideally you should also feed no red meat products beforehand, because red meat may give a false positive. I was reluctant to restrict Ollie's diet because he was already anaemic and not eating too well, but Ollie seemed to do well enough on chicken-based foods. Do check what you are feeding though, many commercial foods contain more than one meat source.

Veterinary Partner has some helpful information on gastro-intestinal bleeding.

Effect of dietary factors on the detection of fecal occult blood in cats (2001) Tuffli SP, Gaschen F & Neiger R Journal of Veterinary Diagnostic Investigation 13(2) pp177-9 explains more about dietary restrictions and concludes "Both tested kits are clinically useful for occult blood in cat feces; however, the diet fed prior to testing must be taken into consideration, and dietary restrictions are advisable before testing."

Palpation of Kidneys Back to Page Index

The first thing your vet will do is usually a physical examination of the kidneys by palpating (feeling and moving) them through the skin. This will tell your vet whether the kidneys feel small or large (renomegaly) and he/she may also be able to feel scar tissue, although kidney palpation alone is not sufficient for a diagnosis.

Most CKD cats, though by no means all, have small, scarred kidneys.

Oral Check Back to Page Index

Many cats with CKD have dental problems, which in some cases may even have contributed to the development of CKD. It is therefore important for your vet to keep a close eye on your cat's mouth and to treat any dental disease, and also to look for mouth ulcers. Most vets will examine your cat's mouth routinely at visits, but many dental problems are invisible to the naked eye.

There is a page devoted to dental problems.

Ultrasound Back to Page Index

This allows the vet to examine the kidneys to check their size and to look for certain abnormalities.Some vets perform ultrasounds routinely, but they are unlikely to be worthwhile if kidneys are small, though are worth considering if kidneys are larger than expected, or if the vet thinks kidney stones might be present..

Ultrasound can also be helpful in diagnosing the existence of a kidney infection (pyelonephritis). In these cases, the renal pelvis may be dilated (this is known as pyelectasis), which would be visible on ultrasound. This dilation may also occur when kidney stones are present. Ultrasound may also be helpful in diagnosing urinary tract infections, but only if the bladder is full. In all cases you need an experienced operator.

Where a type of kidney disease called Polycystic Kidney Disease (PKD) is suspected, an ultrasound can give you some idea how advanced the condition is.

Ultrasounds are not invasive and can usually be done without anaesthesia or even sedation, so there is no need to fast the cat beforehand. The cat may need to be shaved at the examination site (although my extremely fluffy Chinchilla Persian had a cardiac ultrasound without being shaved). Cold gel has to be applied to the body to allow the equipment to work properly, which may be a little uncomfortable when first applied (ask if you can warm it a little in your hands first), but all my cats who have had ultrasounds coped just fine.

Long Beach Animal Hospital has information on ultrasounds (note: the needle shown is not used during ultrasounds of hearts or kidneys!; that is for a stomach biopsy, performed under anaesthesia).

Diagnostic imaging: ultrasound of cats with chronic kidney failure not always black and white (2008) Zwingenberger A DVM News Magazine explains how CKD kidneys look different to healthy ones.

Pet Place explains more about abdominal ultrasounds (no need to register to read the article, just click on Close at the bottom of the irritating pop-up).

X-Rays Back to Page Index

X-rays can be used to look at the kidneys and to check for stones, but in most cases palpation and, if necessary, the use of ultrasound make the use of x-rays unnecessary.

X-rays may require the cat to be sedated. Some members of Tanya's CRF Support Group have been allowed to don lead aprons and hold their cats still for the x-ray instead, but not every vet permits this.

Long Beach Animal Hospital has information on x-rays.

Intravenous Pyelogram (IVP) Back to Page Index

An IVP is a special type of X-ray which uses a contrast agent to clearly show the urinary tract. IVPs may be used when tumours or blockages are suspected. However, the dyes used as a contrast agent may be toxic to the kidneys, particularly if there is a blockage, so this must be borne on mind when deciding whether to have this procedure.

Children's Health System has information on this procedure in humans.

Planar Renal Scintigraphy Back to Page Index

This is a less invasive way of evaluating renal function and does not require anaesthesia in most cases. However, it is normally only used to assess kidney function prior to removing a kidney because of a tumour or prior to a nephrectomy (cutting into the kidney, e.g. to remove kidney stones). It is unlikely to be of any benefit for the typical CKD cat with small, scared kidneys.

Advanced Medical Veterinary Imaging has a helpful overview of renal scintigraphy.

Biopsy Back to Page Index

This may be used in cases where cancer is suspected. Since it requires an anaesthetic, it should only be done where absolutely necessary. For general CKD cases, it is unlikely that a biopsy will be of sufficient value to justify the risks associated with it, but discuss this in more detail with your vet - there may be a valid reason in your cat's case.

Renal biopsies: what are some benefits and risks is an interesting article by Dr Carl Osbourne of the College of Veterinary Medicine at the University of Minnesota.

Renal biopsy in the cat and dog is an overview of biopsies by Idexx Reference Laboratories.

Renomegaly (Enlarged Kidneys) Back to Page Index

Most CKD cats have small, scarred kidneys. However this is not always the case. Cats with a disease called Polycystic Kidney Disease (PKD) usually have large, swollen kidneys. Cats with renal lymphoma, a form of cancer, may also have large kidneys, as may cats with perinephric pseudocysts. Another condition called hydronephrosis may cause enlargement of the kidneys with urine because of obstruction of the ureter, which prevents urine from passing through. Cats with acute renal failure may have enlarged kidneys.

Occasionally a cat will have one small kidney and one large kidney, a condition known with startling originality as "big kidney little kidney syndrome". This is commonly caused by stones or obstructions.

DVM News Magazine has more information on renomegaly.

Pet Place has information on hydronephrosis (no need to register to read the article, just click on Close at the bottom of the irritating pop-up).

Cats with chronic renal failure (CRF) - how different than CRF in dogs? (2007) is a presentation by Drs DJ Chew and SP DiBartola to the World Small Animal Veterinary World Congress which mentions big kidney little kidney syndrome.

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This page last updated: 02 December 2011

Links on this page last checked: 24 November 2011