Urinalysis & Imaging

Quick Answer: Urine tests, particularly urine specific gravity, can pick up early signs of CKD and help confirm a diagnosis alongside bloodwork. The complete blood count mainly rules infection in or out on the white blood cell side, since the red blood cell side is covered in detail on our anemia page. Imaging, especially ultrasound, is not always run automatically but is increasingly recommended at diagnosis, and is essential if kidney stones, infection, or a structural problem is suspected.

A urine sample gives your vet information that blood tests alone cannot, and all of it typically comes from a single sample. The main things it reveals for a CKD cat are how well the kidneys are concentrating urine, whether protein is leaking into the urine, and whether an infection is present.

Samples can be collected at home using a free catch method or non-absorbent litter, though these are not sterile and are not suitable if your vet needs to run a culture to check for infection. For that, a sterile sample taken by needle directly from the bladder, called cystocentesis, is needed, and despite how it sounds, most cats tolerate it well.

Urine specific gravity (USG) measures how concentrated the urine is, and it is one of the more useful early clues for CKD, since kidneys typically lose their concentrating ability before other changes show up in bloodwork.

Healthy, well-hydrated cats typically produce urine in the range of 1.035 to 1.060. A reading consistently below about 1.035 to 1.040 is generally considered a problem, and most CKD cats run considerably lower than that, often between 1.008 and 1.012, a state referred to as isosthenuria. That said, USG should never be read in isolation, since it naturally varies with how much a cat is drinking, whether they eat wet or dry food, and the time of day the sample was collected, and it becomes fairly unreliable once a cat is receiving regular fluid therapy. A low USG can also show up with conditions other than CKD, including diabetes, hyperthyroidism, and certain dental problems, so your vet will usually want to see it more than once, alongside bloodwork, before relying on it for a diagnosis.

Protein in the urine, known as proteinuria, is both a risk factor for CKD progression and one of the measures used to help stage the disease once it is diagnosed. We cover proteinuria in detail, including the UPC ratio used to measure it, on our dedicated proteinuria page.

Urinalysis is also a key tool for catching kidney and urinary tract infections, which are worth watching for in CKD cats since infections can accelerate kidney damage if left untreated. We go into the diagnosis and treatment of these infections on our pyelonephritis and UTI page.

The complete blood count is usually run from the same blood draw as the chemistry panel, and for a CKD cat it serves two main purposes. One is checking for anemia, which we cover in full on our anemia page since it is common enough in CKD to warrant its own detailed discussion. The other is looking at white blood cells, which can point toward infection or inflammation somewhere in the body. An elevated white blood cell count is common in acute kidney injury in particular, due to the buildup of toxins and associated inflammation, while a cat dealing with a more chronic, low-grade illness sometimes shows the opposite pattern of lower than normal white blood cells.

Ultrasound lets your vet look directly at the kidneys’ size, shape, and internal structure, and it does not usually require sedation or fasting, which makes it a relatively low-stress test for most cats.

It was once thought that ultrasound added little for a straightforward CKD diagnosis, since a cat can have significant kidney dysfunction with a fairly unremarkable-looking ultrasound, and vice versa. More recent research has shifted that view somewhat, suggesting that a baseline ultrasound at initial diagnosis is worthwhile for most CKD cats, since it can catch problems that bloodwork alone would miss.

Ultrasound is particularly worth prioritizing if any of the following are suspected: kidney stones, a kidney or urinary tract infection, polycystic kidney disease, an enlarged kidney, or certain cancers. Healthy cat kidneys typically show up as smooth and bean shaped, while CKD kidneys tend to look smaller and more irregular in outline. Occasionally a cat will show up with one shrunken kidney and one enlarged kidney, usually because a stone or blockage has damaged one side while the other has grown to compensate, a pattern sometimes referred to informally as big kidney, little kidney.

Whoever performs the ultrasound, ideally an experienced radiologist, is important. A poorly performed or poorly interpreted ultrasound can be misleading, so it is worth asking about the experience level of whoever is doing your cat’s scan.

X-rays are used less often for CKD specifically, since palpation and ultrasound generally provide the information needed. They can be useful for confirming kidney stones or, using a specialized contrast dye version, for evaluating the urinary tract more clearly when a blockage or tumor is suspected, though the contrast dye itself carries some risk to already compromised kidneys.

A kidney biopsy is rarely needed for typical CKD cases, since it requires anesthesia and carries a real risk of complications, most commonly bleeding. It is occasionally recommended in more specific situations, such as an enlarged kidney of unclear cause, CKD appearing in an unusually young cat, persistent and severe proteinuria, or when acute kidney injury needs a clearer prognosis. This is a decision worth making carefully with your vet, weighing the risk against how much the result would actually change your cat’s treatment.

My cat’s USG looked normal even though the vet suspects CKD. Is that possible? Yes, occasionally a cat with CKD and elevated kidney values on bloodwork will still show a higher than expected USG. It does not rule out CKD on its own, particularly if other kidney values remain persistently elevated.

Do all CKD cats need an ultrasound? Not strictly, but it is increasingly recommended at initial diagnosis, since it can catch structural problems that bloodwork cannot. It becomes more clearly worthwhile if stones, infection, or an unusual kidney shape on palpation is suspected.

Is a urine sample from home litter good enough, or do I need a vet visit? A home sample is fine for basic screening tests like USG and general appearance, but it is not sterile, so it cannot be used to test for infection through a culture. If infection is a concern, your vet will need to collect a sample directly.

Should I be worried if my cat’s white blood cells are elevated? Not automatically. It can reflect infection or inflammation, but it can also happen with stress, certain medications, or simply a difficult blood draw. Your vet will usually look at the full picture, including the type of white blood cells involved, rather than the total count alone.

• Using urine specific gravity (2024) Watson ADJ, Lefebvre HP & Elliott J International Renal Interest Society
• ISFM consensus guidelines on the diagnosis and management of feline chronic kidney disease (2016) Sparkes AH, Caney S, Chalhoub S, Elliott J, Finch N, Gajanayake I, Langston C, Lefebvre H, White J & Quimby J Journal of Feline Medicine & Surgery 18 pp219-239
• Pilot study to evaluate the potential use of the renal resistive index as a preliminary diagnostic tool for chronic kidney disease in cats (2018) Matos I, Azevedo P & Carreira LM Journal of Feline Medicine and Surgery 20(10) pp940-947
• Renal pelvic and ureteral ultrasonographic characteristics of cats with chronic kidney disease in comparison with normal cats, and cats with pyelonephritis or ureteral obstruction (2017) Quimby JM, Dowers K, Herndon AK, Randall EK Journal of Feline Medicine and Surgery 19(8) pp784-790
• Evaluation of and the prognostic factors for cats with big kidney-little kidney syndrome (2021) Wu Y-T, Hung W-C, Huang P-Y, Tsai H-J, Wu C-H & Lee YJ Journal of Veterinary Internal Medicine 35(6) pp2787-2796
• Renal biopsy: a retrospective study of methods and complications in 283 dogs and 65 cats (2005) Vaden SL, Levine JF, Lees GE, Groman RP, Grauer GF & Forrester SD Journal of Veterinary Internal Medicine 19(6) pp794-801
• IRIS treatment recommendations for CKD in cats (2023) International Renal Interest Society