How to Use Fluorescein Stain When Cats Urinate Outside the Litter Box

Do you need to know which cat is urinating outside the litter box? I recently got this question from a very frustrated cat lover with 6 cats. It seems that one of them was urinating on the carpet in the dining room and in her bed! Despite watching her cats closely she has never caught one "in the act" and wanted to know how to find the guilty party.

How can you tell which cat is urinating outside the litter box in a multicat home? One very effective method is the use of fluorescein stain.

How to Use Fluorescein Stain When Cats Urinate Outside the Litter Box

Fluorescein stain is a pet-safe common dye used to diagnose ulcers on the cornea of the eye. It is sometimes used to help owners determine which cat is inappropriately eliminating. Go here for more information on how it is used in dogs.

This stain is typically given to cats by way of a small, digestible piece of paper inside of a gelatin capsule. The dye on the paper makes its way safely through the cat's digestive system. When a cat who has received the dye urinates, the waste is typically a bright yellow or apple green color. By observing the color of the inappropriate urine, you can tell which cat eliminated there.

Dosage works like this: pick one cat to monitor and give them one capsule with dyed paper. Monitor the urine for 24 to 48 hours. If you do not see any inappropriate urination you can try for one more day. If the inappropriate urine is not brightly colored, you will know it is not that cat.

For home with more than 2 cats, you can still use the dye to determine "whodunit." If your test with the first cat yields no conclusions, wait 48 hours and give a different cat the dye capsule. Repeat until you identify the source of the urine.

Although the bright color of the urine can usually be seen without the aid of a black light, using one can help. These can be purchased at most pet stores near carpet cleaning solutions. They will often resemble small handheld flashlights or wands.

Please note that fluorescein dye is considered water soluble but will stain some carpets and fabrics, so you will want to use it sparingly.

I recommend giving the dye very early in the morning and monitoring the patient for 24 to 48 hours. This can depend on how many cats you have and how much time you have to spend doing observation.

I hope this tip helps you figure out which cat is urinating outside the litter box in your home.