The American Veterinary Medical Association estimates that 25% of US households own cats. If so, you may have seen targeted advertisements for a health-monitoring cat litter on the internet. These items claim to react to certain disease indicators in a cat’s urine by changing color, assisting owners in identifying early sickness symptoms before more severe ones appear.

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According to Jody Lulich, a small-animal internal medicine specialist at the University of Minnesota College of Veterinary Medicine, “the goal with any disease is to pick up disease early, not late.” A disease’s chances of recovery are higher the sooner it is discovered.

Per the Cornell Feline Health Center website, cats are more likely to experience urinary tract problems as they age or become overweight. Since litter is used to absorb urine, it seems sense that health-monitoring cat litters concentrate on looking for any issues with a cat’s urinary system, which includes the kidneys, bladder, and the plumbing that links them. However, how can these litters achieve that? C&EN made the decision to investigate and learn more.

A fascinating subject

In contrast to certain other consumer items, like urine-testing dipsticks, which are useful for monitoring a cat’s urinary health at home, health-monitoring litters also need to be used like regular cat litter. This implies that, ideally without creating too much dust, their primary purpose is to absorb moisture and smells from your cat’s excretory activity.

According to Mariangela Imbrenda of the Clorox firm, the parent firm of the Fresh Step litter brand, clay makes up the majority of cat litters—roughly 92%. Nevertheless, silica, which makes up around 2% of the litter industry overall, is used to make indicator litters. The various organic litter items, such as maize, wood, paper, and even tofu, make up the remaining 6%.

Made from amorphous silica gel, which is frequently found in packets inside shoe boxes and bags of jerky to keep those goods dry, silica litter, also referred to as “crystal” litter, is sold. Numerous microscopic holes in the silicon and oxygen structure of silica gel are designed to absorb small molecules that have the potential to form hydrogen bonds. These molecules are water and ammonium ions, which are created when bacteria in urine break down urea, in cat litter. Ammonium is the source of a dirty litter box’s strong odor.

While silica litter is more costly and doesn’t clump like other clay litters, it is often lighter, less dusty, and more effective at capturing moisture and odor-causing molecules—it can absorb up to 35% of its weight in water without expanding. Additionally, pure silica gel is naturally white, which may aid in the appearance of colors if dyes are added during the production process. One example of this would be color-changing indicators used to examine a cat’s urine.

The fundamentals of colorimetry

According to Jessica Beard, a PhD candidate in chemistry at the Massachusetts Institute of Technology who is creating colorimetric tests for the detection of water contaminants, an important part of every chemical test is a reaction to a chemical interaction. A color shift is the result of a colorimetric test.

According to Beard, colorimetric indicators are helpful for tests in which complex equipment is not desired since it is possible to make the results obvious to the naked eye. Furthermore, she notes that commercial indicators frequently rely on long-established chemistry, which is a significant benefit. “It’s probably tolerant of a lot of interference if they could get it to work in the early 1900s.”

According to veterinary specialist Lulich, using colorimetric assays for a fast urine analysis is nothing new. Veterinarians first use a dipstick test strip with colorimetric markers to evaluate a pet’s urine; if required, they can next do more specialized testing. These test strips could test for pH as well as specific illness signs like blood, protein, or glucose.

The primary characteristic promoted by health-monitoring cat litters is their capacity to identify pH variations through color. When C&EN tested the pH-indicating ability of a bag of litter by getting our hands dirty, we saw just that. Indicator component bromothymol blue is present, according to the company’s patent. When this substance is deprotonated (pH 7.6), it is blue, and when it is protonated (pH 6) it is yellow. Green hues vary in solutions containing a mixture of protonated and deprotonated molecules.

In the at-home experiments conducted by C&EN, the litter became yellowish green when filtered water (pH of about neutral) was used, orangey-yellow when vinegar water (pH of about 3) was used, and vivid blue when baking soda was added to water (pH of about 8). After a few hours, the orange and yellow hues disappeared, which Beard speculates might be the result of a proton transfer between the indicator and the silica. The blue stayed blue.

Suggesting an issue?

The Merck Veterinary Manual states that cat pee typically has a pH of 6.3–6.6. It also states that some bacterial illnesses can cause alkaline urine, and that the pH of urine might influence the development of bladder stones. However, a cat’s urinary system can withstand a significant amount of pH change, according to Lulich. He states that “the body is going to get rid of it if the animal takes in a lot of alkali.” This also applies to excessive acid production or consumption. “If the body can eliminate it, then it isn’t abnormal.”

It did not reply to inquiries on the contents of the litter by the date set by C&EN, but since the indicator is bromothymol blue, it is most likely warning cat owners about urine that is above pH 7.6 and below pH 6. Since “pH is not very useful by itself,” according to Lulich, a pH reading outside of that range may indicate that a cat is ill, but it can also alter for entirely unrelated causes. Rather, veterinarians will take into account pH levels in conjunction with additional symptoms and risk factors such the age, food, and medical background of the cat.

Blood in the pee is another feature that many health-monitoring litters are meant to detect. That test could be far more useful. Blood in the pee, according to Lulich, can indicate a variety of dangerous illnesses. He claims that almost every detectable level warrants further investigation.

Medical-grade urine test strips detect blood in the clinic by using 3,3′,5,5′-tetramethylbenzidine and diisopropylbenzene dihydroperoxide. Hemoglobin, which is found in blood, includes iron (II). In the event that the urine test contains any hemoglobin, the iron(II) and peroxide molecules will react, forming radicals. The tetramethylbenzidine subsequently undergoes oxidation by the radicals, changing its hue from yellow to blue green.

However, three manufacturers claim that if a cat urinates and there is blood in it, the blood-detecting litter will turn red instead of blue. C&EN conducted tests using various amounts of hemoglobin in water with the assistance of Matthew Hartings, a scientist at American University. Hartings is on the advisory board for C&EN. C&EN discovered that the hue of the hemoglobin solution was mirrored in the color of the litter. Therefore, it appears that blood detection, at least for that purpose, depends less on a chemical test and more on the contrast between the reddish hue of bloody urine and a white background.

While Lulich warns against drawing too many conclusions from a single data point, he says he views at-home pet health monitoring as generally beneficial since it helps facilitate communication between veterinarians and pet owners, which may improve health outcomes. He claims that just your wallet will be harmed. “If early disease detection can be achieved while avoiding unnecessary and potentially harmful testing, then the answer should be positive.”