Color-changing litters and smart litter box monitors can flag a change worth checking. They cannot diagnose anything. Here is how to read them and when to go straight to a vet.
Color-changing litter: What it watches — Urine pH and blood, by color; Examples — PrettyLitter (silica crystal litter); Main limitation — One reading per clump; pH swings with diet and time of day.
Indicator granules or test cards: What it watches — Urine pH and blood, mixed into or used with normal litter; Examples — Sold as add-ons to your usual litter; Main limitation — Same limits; easy to miss a reading.
Smart litter box or monitor: What it watches — Visits, time in the box and, on some models, the cat's weight; Examples — Litter-Robot 4 (Whisker app), Purina Petivity monitor; Main limitation — Tracks behaviour, not urine chemistry; needs Wi-Fi and an app.
Color-changing litters generally use a neutral base color, one color for alkaline urine, another for acidic urine and red for blood. PrettyLitter, for example, describes blue as alkaline, orange as acidic and red as a sign of blood. Check the chart for the product you use; the colors are not standard between brands.
Alkaline urine is associated with struvite crystals and some bacterial infections, but it also happens after a meal, with some diets, and if a sample sits.
Acidic urine can be associated with some metabolic and kidney problems, and also with high-protein diets.
Blood is the most useful signal. Blood in the urine is a reason to call your vet whatever the litter says.
A single odd color is not an emergency. A color that repeats for several days, or any red, is worth a vet visit with a fresh urine sample.
Watch the cat, not just the litter. Call a vet the same day if your cat:
strains in the box and produces little or no urine — in a male cat this can be a urethral blockage, which is an emergency;
goes to the box far more often than usual, or cries while urinating;
urinates outside the box, especially on cool smooth surfaces such as sinks and baths;
drinks noticeably more, or produces much larger clumps than usual — a classic early sign of kidney disease or diabetes, which pH litter does not detect.
They watch something different. A monitor that logs every visit can show that a cat is going twice as often as last week, which is one of the earliest signs of urinary trouble and something an owner with several cats would never notice. Some models also log the cat's weight on each visit, according to their makers, and steady weight loss in an older cat is worth a vet visit on its own. The trade-offs are cost, an app and Wi-Fi, and false alarms when two cats share a box.
1. Learn the baseline: note the usual color for a week before reading anything into a change.
2. Look at the same time of day, on fresh clumps, because readings change as a clump sits.
3. Write down any change with the date, so you can tell your vet when it started.
4. Take a fresh urine sample to the vet in a clean container if the change repeats; many vets also sell non-absorbent litter for collecting one.
5. Keep using the basics: one box per cat plus one, scooped daily. Most litter problems are box problems.
For clumping, crystal and natural litters compared on dust, odor and cost, see our cat litter guide.
Cornell Feline Health Center — feline lower urinary tract disease. vet.cornell.edu
International Cat Care — cystitis and urinary tract disease in cats. icatcare.org
American Association of Feline Practitioners and ISFM — guidelines on house-soiling and litter box management. catvets.com
PrettyLitter and Whisker (Litter-Robot) — manufacturers' published product descriptions.
It works as a prompt, not a test. The indicators do react to urine pH and blood, but pH changes with diet and time of day, and a normal color does not rule out infection, crystals, kidney disease or diabetes. Treat a repeated change, or any red, as a reason to take a urine sample to your vet.
PrettyLitter describes blue as alkaline urine, which can go with struvite crystals or some infections but also happens after meals and with some diets. If it repeats for several days, ask your vet to test a fresh sample.
pH and blood indicators do not detect them. More frequent visits and larger urine clumps are earlier clues, which is where a smart litter box monitor that logs visits can help. Your vet confirms either condition with blood and urine tests.
No. Straining with little or no urine, especially in a male cat, can mean a urethral blockage, which can be fatal within a day or two. Call a vet or emergency clinic now.