Cat urine

My 17.5 yr old tuxedo make has a bit of froth/bubbles in his urine. Not sure if it’s from interaction with litter or high protein in his urine 

Hello!  Your vet can check for protein in the urine easily enough, by using a protein dipstick on a fresh sample.  It can be helpful to pick up warning signs of other diseases too such as diabetes and (with a refractometer) kidney disease, so your vet may be happy to do this for your old cat if you can provide a fresh sample.   I have never heard of bubbles in urine as a warning sign of protein, but a urine test may be a useful way in which to find out.  If your vet knows something I don't know about this, please do let me know!    

Was just something I had heard and looked it up. I know of course you can’t believe everything you read, so that’s why I asked. Thank you so much for your reply!!