Have Cat Questions? Ask a Cat Vet Online.
I am sorry both you and your cat are going through this. I will certainly try to help.
Although I have never personally seen green urine, this is absolutely not normal. It could indicate infection. If you had him tested over a year ago, this is very outdated and things could have changed (that is the equivalent of about 8 years in his life span). If there hasn't been any major changes in his environment or stressful events, and if you have large, uncovered litter boxes, at least one per cat, this is probably a medical problem and should be addressed asap, especially since he is male.
First of all, there are 4 major medical conditions that occur that can cause urinating outside the box:
cystitis (sterile inflammation)
infection (least common)
The absolutely most important thing you can do is to have his urine checked and cultured (the best way to rule out infection). If he has anything other than an obvious infection, all other conditions have been linked to feeding dry foods (most any brand), and especially those foods with grains as fillers. The current recommendation for feeding cats is summarized on www.catinfo.org.
Dry foods over concentrate the urine and cause all 3 conditions except infection due to lack of moisture. Most all dry foods today contain lots of grains as low quality protein sources (corn, wheat, soy, rice). These are added to increase pet food companies profit margins, but are a very un-natural protein source for cats. The not only create metabolic waste products in the urine that cats were never designed to deal with, grains increase the ph of the urine, which predisposes them to all these conditions. Yes, there are "urinary" formulas out there, but they changed the ph with chemicals, not naturally.
Some canned, grain free brands to look for are Innova Evo, Wellness Core, Pinnacle, Instinct, Before Grain, Weruva, and others. They are usually available at private pet stores and on line.
Please have his urine checked before this becomes more serious! If it is completely normal, I would be glad to help you trouble shoot a behavioral problem. If it is an infection, make sure you check his teeth (rear upper molars) because dental disease is a big cause of urinary tract infections.
If you need a vet that is good with cats, try www.catvets.com.
Thanks for your question. Let me know if I can do anything else.