The Urinalysis, Annotated

Some of the oldest books print a short text mid-page, ringed by centuries of commentary. The urinalysis deserves the same. It’s short, dense, cryptic, and handed over at a frightening moment with one sentence of summary.

This is the commentary. It won’t let you interpret your own cat’s results — that takes the whole clinical picture and a vet. It will let you follow the conversation.

A lab report is a text. Read it twice.

§ 1How it was collected

The most important fact about a sample isn’t printed in its results. It’s how the urine got into the pot.

• Cystocentesis. A fine needle through the belly wall into the bladder. Sounds alarming, generally well tolerated, cleanest sample. The method of choice for culture: bacteria found here mean real infection.
• Catheter. A tube up the urethra; common in a blocked cat anyway. Can add a few cells or a little blood.
• Free catch. Caught mid-stream, or from a clean box at home. Easy and fine for many purposes, but lower-tract bacteria can contaminate it.

Then time. Best examined within about thirty minutes; usually fine refrigerated for up to a day. But cold can precipitate crystals in the pot that were never in the cat. Crystals in an old, cold sample are partly a report on the refrigerator. Ask when it was run.

§ 2Color and clarity

Normal cat urine is yellow and clear. Red, pink or brown suggests blood or blood pigments. Cloudiness can be cells, crystals, mucus or bacteria. A table of contents, not a chapter: it tells the lab where to look.

§ 3Specific gravity

The most important number for a urinary cat. Write it down.

It compares the urine’s density with water, 1.000. Higher means more concentrated. It should be read with a refractometer, ideally calibrated for cats — a human-calibrated one reads cat urine falsely high. The dipstick’s specific-gravity pad isn’t valid in animals. Ignore it.

Cats concentrate formidably. At or above roughly 1.035, a cat is showing its kidneys concentrate well. But for a cat with cystitis or stones the goal is usually lower — below somewhere around 1.030 to 1.040 — because dilute urine irritates less and grows fewer crystals. Track it across rechecks; it tells you whether the water project works.

Persistently low specific gravity in a cat not being deliberately diluted, especially one drinking more, is a different conversation, usually about kidneys and hormones.

The water project has one scoreboard. This is it.

§ 4The dipstick

A strip of pads that change color. Fast, cheap, useful — with exceptions in cats.

• pH. Matters mostly for stones: struvite forms more readily in alkaline urine, calcium oxalate in acidic. One reading swings with meals and sample age; a trend means more. Don’t push it with over-the-counter acidifiers without knowing the stone type.
• Protein. From inflammation or bleeding in the lower tract, or from the kidneys. The pad gives false positives more often in cats than dogs — partly a normal cat protein called cauxin, partly concentrated, alkaline urine. If kidney loss is suspected, the lab runs a urine protein-to-creatinine ratio: in cats, under about 0.4 is generally normal, over 1 abnormal, borderline between.
• Glucose. Normally absent. Diabetes is the classic cause. Stress can raise a cat’s blood sugar too, so one finding is read in context.
• Ketones. Normally absent. With glucose, they suggest poorly controlled diabetes. Taken seriously.
• Bilirubin. In dogs a trace can be normal. In cats, bilirubin in the urine is never normal — it prompts questions about the liver or red-cell destruction.
• Blood. Very often positive in FLUTD. Confirmed and counted under the microscope.
• Pads to ignore. White cells (leukocyte esterase), nitrite, specific gravity. Designed for human urine; not valid in animals.

Three pads on the strip are, for a cat, decorative.

§ 5The sediment

Spin the sample, look at what settles. Much of the real work happens here.

• Red cells. Fewer than about five per high-power field is normal. More means bleeding — cystitis, stones, obstruction, or the collection itself.
• White cells. Fewer than about five is normal. More means inflammation, infectious or not.
• Bacteria. In a cystocentesis sample, infection. In other samples, possibly contamination. Hence culture.
• Epithelial cells. Shed lining. Some are normal.
• Casts. Tiny molds of the kidney’s tubules. A few of certain kinds are normal; many point to the kidneys.

§ 6Crystals, overrated

The thing owners remember. The literature is emphatic: crystals are not stones, and not necessarily disease. Healthy cats can have them. They can form in the pot after collection. Stones can form without them ever showing up.

The type still matters. Struvite is common, and cats — unlike dogs — can form struvite stones without infection. Calcium oxalate forms in more acidic urine; persistent oxalate crystals may mean higher stone risk. In a blocked male, crystals are often part of the plug. In cystitis without obstruction, they may be incidental.

If the report says crystals present, ask: which kind, how many, how fresh was the sample, and anything on imaging?

§ 7The culture

A urinalysis can suggest infection. Only a culture confirms it. Part of the sample — ideally by cystocentesis — goes on growth media for a few days. If bacteria grow, the lab names them and tests which antibiotics work. In young and middle-aged cats, where most urinary disease isn’t bacterial, this is why many vets won’t prescribe antibiotics without it.

§ 8The report as a whole

§ 9What to ask

1. How was the sample collected, and how long before it was run?
2. What was the specific gravity, and what are we aiming for?
3. Crystals? Which kind? Do they matter here?
4. Any evidence of infection? Are we culturing?
5. Anything pointing beyond the bladder — kidneys, diabetes, liver?
6. When do we repeat it, and what should change?

Keep every report in one folder, in order. Read as a whole, each part against the others, the archive tells what no single report can.

Works cited

1. Merck Veterinary Manual. “Urinalysis.” Clinical Pathology and Procedures.
2. Grauer G.F., Pohlman L.M. “Urinalysis Interpretation in Canine & Feline Patients.” Clinician’s Brief, 2016.
3. Cornell Feline Health Center. Feline Lower Urinary Tract Disease. Cornell University College of Veterinary Medicine.
4. Today’s Veterinary Practice. “Diagnosing and Managing Feline Lower Urinary Tract Disease.”
5. He C., et al. “Prevalence, Risk Factors, Pathophysiology, Potential Biomarkers and Management of Feline Idiopathic Cystitis: An Update Review.” Frontiers in Veterinary Science, 2022.