Urinalysis basics: USG, protein, and what they reveal

Articles · Lab Values

A urinalysis is one of the most underrated tests on a cat’s panel. It often shifts before the blood numbers do, which is why your vet wants a urine sample alongside the bloodwork. This guide explains urine specific gravity, urine protein, and the UPC ratio in plain language, and why they reveal so much.

What is urine specific gravity (USG), and what is normal for a cat?

Urine specific gravity (USG) measures how concentrated your cat’s urine is, in other words, how well the kidneys are pulling water back out of the urine. Healthy cat kidneys produce highly concentrated urine, so a well-functioning cat typically has a USG above about 1.035. A low USG can mean the kidneys are losing their ability to concentrate.

A quick reference, from clinical pathology and IRIS resources:

• Above ~1.035: the cat is concentrating urine well. Cats normally make more concentrated urine than dogs.
• 1.008 to 1.012 (isosthenuria): the urine is no more or less concentrated than blood plasma, which suggests the kidneys are not concentrating effectively.
• Wide normal variation exists: a hydrated, healthy cat’s USG can range widely, so one value is read together with hydration status and blood results.

Why does urine concentration shift before blood values do?

The kidneys lose their ability to concentrate urine relatively early, often before waste products like creatinine climb in the blood. So a falling USG can be an early hint of kidney change while the chemistry panel still looks normal. That early-warning quality is exactly why a urinalysis adds so much to a senior-cat work-up.

Here is the logic vets use:

• A cat with dilute urine plus a normal creatinine raises the question of early kidney change, since healthy feline kidneys should be concentrating.
• A cat with dilute urine and a high creatinine points more clearly toward kidney involvement.
• USG also helps interpret a high creatinine: well-concentrated urine alongside high creatinine suggests dehydration (pre-renal) rather than kidney damage.

This pairing is why your vet ideally wants urine and blood from around the same time. For how the kidney picture fits together, see our guide for CKD cats and our overview of SDMA.

What does protein in the urine mean?

Protein in the urine (proteinuria) can be an important marker of kidney health, because healthy kidneys keep most protein in the bloodstream. Persistent protein loss through the kidneys is associated with faster progression of kidney disease, so it is something vets watch and quantify rather than ignore. A trace on a dipstick, though, is just a starting point.

Why a dipstick alone is not enough:

• A urine dipstick is a rough screen and can be affected by how concentrated the urine is.
• To measure protein loss properly, vets calculate the urine protein-to-creatinine ratio (UPC), which corrects for concentration.
• Proteinuria should be confirmed as persistent (on more than one sample) and the urine checked for infection or inflammation, which can also raise protein.

How is the UPC ratio interpreted in cats?

The UPC ratio quantifies how much protein the kidneys are leaking, corrected for urine concentration, so it is far more reliable than a dipstick. In cats, broadly accepted reference points are: under 0.2 is non-proteinuric, 0.2 to 0.4 is borderline, and above 0.4 is proteinuric and worth attention. These thresholds feed directly into kidney-disease staging.

How vets use those bands:

• UPC under 0.2: considered non-proteinuric.
• UPC 0.2 to 0.4: borderline; usually rechecked to see if it is rising or stable.
• UPC above 0.4: significant protein loss in a cat, which the International Renal Interest Society (IRIS Staging of CKD, 2023) uses to sub-stage kidney disease alongside creatinine and blood pressure.

Because borderline values are common, a single UPC is often confirmed on a fresh sample, ideally without active urinary infection.

What else does a urinalysis check besides USG and protein?

A full urinalysis also examines the urine sediment and runs several chemical tests, which together can reveal infection, inflammation, crystals, or metabolic clues. So beyond concentration and protein, the same sample can flag a urinary tract infection or hint at conditions like diabetes. That breadth is part of why it pairs so well with bloodwork.

Other things a urinalysis looks at:

• Glucose: sugar in the urine can be a clue to diabetes, prompting a look at the blood glucose. Our guide for diabetic cats covers this further.
• Blood and white cells / bacteria: can point to infection or inflammation in the urinary tract.
• Crystals and pH: relevant to bladder stones and urinary health.
• Casts and cells in the sediment: can reflect changes within the kidney itself.

Because some of these (like infection) can also affect protein readings, the sediment helps your vet interpret a high UPC correctly.

Why does the way the sample is collected matter?

How urine is collected affects which tests are reliable, especially infection cultures and the UPC. A sample caught from a clean litter tray is fine for screening concentration, but a sterile sample collected directly from the bladder is preferred when an accurate culture or a clean protein measurement is needed. This is why your vet may ask to collect it a particular way.

Collection considerations:

• Free-catch samples are easy and useful for USG and basic screening, but can pick up contaminants.
• Cystocentesis (a sterile sample drawn directly from the bladder) is preferred for urine culture and for a clean UPC.
• Timing matters too: a urine sample taken close to the bloodwork lets your vet compare urine concentration against the blood values from the same window.

None of this is something you need to manage yourself; it is just helpful to understand why your vet handles collection deliberately.

What should I ask my vet about my cat’s urinalysis?

Ask what the USG says about your cat’s hydration and kidney concentration, whether any protein found was confirmed with a UPC, and how the urine results line up with the bloodwork. Those questions tie the urinalysis to the rest of the picture, which is how it becomes genuinely useful rather than a page of isolated values.

Helpful follow-ups include:

• Does the USG suggest dehydration or reduced concentrating ability?
• Should we confirm any proteinuria with a repeat UPC?
• Was a urine sample taken close in time to the bloodwork?

How can I track urine and hydration trends at home?

Urine and hydration clues show up at home long before the next test, so logging them adds real value. Pawtient AI’s bathroom tracking lets you note urination patterns and changes day to day, and stores them alongside water intake and lab results, so when your vet reviews a urinalysis you can show what was happening at home. Our lab value translator and FAQ can help with individual values.

Pawtient AI is an AI assistant and second opinion, never a diagnosis — always consult your veterinarian.

Sources

• International Renal Interest Society. IRIS Staging of CKD (modified 2023). iris-kidney.com
• IRIS / eClinPath (Cornell University College of Veterinary Medicine). Urine Specific Gravity and Urine Protein:Creatinine Ratio. iris-kidney.com, eclinpath.com
• WSAVA. A Case-Oriented Approach to Urinary System Laboratory Profiling in Dogs and Cats. World Small Animal Veterinary Association Congress proceedings.

By Pawtient AI Editorial Team. Educational content reviewed against published veterinary guidelines (IRIS, AAHA, WSAVA, ACVIM, AAFP). Not a substitute for veterinary care.