PrettyLitter detects three things in your cat’s urine: high pH (alkaline), low pH (acidic), and the presence of blood. It does this through color-changing silica gel crystals that shift from their baseline dark yellow or olive green when they come into contact with urine that falls outside a typical range. It’s a screening tool, not a diagnostic one, but it can flag problems days or weeks before your cat shows visible symptoms.
How the Color System Works
The litter starts white and turns dark yellow or olive green when it absorbs urine with a normal pH. That’s the color you want to keep seeing. When urine pH shifts significantly in either direction, the crystals change to a different color. Blood detection works differently: there’s no chemical reaction involved. Red-tinged urine is simply visible against the white silica base.
The color change is strongest in the first five minutes to one hour after your cat urinates, then gradually fades. Most of the signal disappears after three to four hours, so checking the box shortly after your cat uses it gives you the clearest reading.
Blue: Alkaline Urine
Blue crystals indicate your cat’s urine pH is higher than normal, meaning it’s too alkaline. This matters because alkaline urine creates favorable conditions for struvite crystals and stones to form. Struvite is a mineral compound that crystallizes more readily at neutral to alkaline pH levels. Urinary tract infections are a common driver of alkaline urine in cats, because bacteria produce enzymes that raise pH.
Healthy cat urine typically falls in the 6.0 to 6.5 range. Research on cats fed a natural diet of whole prey found an average pH closer to 7.0, so there’s some natural variation. But consistently high pH is worth investigating, particularly in combination with other signs like frequent trips to the litter box or straining to urinate.
Orange: Acidic Urine
Orange crystals signal urine that’s more acidic than normal. Acidic urine is associated with calcium oxalate crystals, a different type of stone that has become increasingly common in cats over the past few decades. Diets formulated to produce a urine pH between 6.0 and 6.2 are three times more likely to lead to calcium oxalate stones compared to those targeting a pH of 6.5 to 6.9.
PrettyLitter also notes that orange may reflect metabolic acidosis or kidney tubular acidosis, conditions where the body either produces too much acid or can’t eliminate it properly. These are less common but more serious. Acidic urine also increases calcium loss from bones, which further raises stone risk over time.
Red: Blood in the Urine
Red spots or a pinkish tint in the litter indicate blood, a condition called hematuria. Unlike the pH indicators, this isn’t a chemical reaction. The red color of blood simply shows up against the white silica crystals. The list of possible causes is broad: feline lower urinary tract disorder (FLUTD), bladder stones, kidney stones, bladder inflammation, certain kidney diseases, and clotting disorders. Blood in the urine is never normal and always warrants a veterinary visit, even if your cat seems fine otherwise.
What It Can’t Tell You
PrettyLitter flags that something may be off, but it can’t identify the specific problem. Blue litter tells you urine pH is elevated. It doesn’t tell you whether that’s from a bacterial infection, a dietary issue, or something else entirely. The same applies to orange or red readings. A veterinarian still needs to run a proper urinalysis to pinpoint the cause.
Several factors can also produce misleading results. If litter isn’t changed frequently enough, ammonia buildup from older urine can shift the pH reading of fresh deposits. The silica gel base is chosen specifically because it doesn’t release acid or base ions that would interfere with readings, but environmental contamination (cleaning products near the box, for instance) could theoretically affect results. Multi-cat households add another layer of difficulty, since you may not know which cat produced the color change.
The product also can’t detect conditions that don’t alter urine pH or produce blood. Diabetes, hyperthyroidism, and many other feline illnesses won’t trigger a color change. So a green litter box is reassuring for urinary health specifically, but it’s not a clean bill of health overall.
Why Early Screening Matters for Cats
Cats are notoriously good at hiding pain and illness. A cat with a developing urinary blockage may behave normally until the situation becomes an emergency. Color-changing litter gives you a passive way to catch shifts in urinary chemistry before your cat starts showing obvious distress. Veterinary professionals have noted that these litters can be a useful early detection tool, particularly for cats with a history of urinary issues or breeds prone to bladder stones.
The practical takeaway: treat any persistent color change as a prompt to schedule a vet appointment, not as a diagnosis in itself. A single orange or blue reading could reflect a temporary dietary fluctuation. Repeated abnormal colors over multiple days are a stronger signal that something needs attention.