Glad he's still alive! If this was renal failure I'm quite sure the little guy would have perished long ago... Are you maintaining temps/humidty as per Amy (Lilypad's) directions? When is the last time you saw him poop? Did you have him fecal tested for parasites? What is he eating now? Should be able to eat tiny crickets, small waxworms (on occasion), and very small/baby night crawlers & baby dubia, at this point. Reptocal- Cal/D3 can be given daily, except for the one day a week he should have a multi-vit. I would give him bottled spring water treated with Reptisafe to soak in; If you have live plants in the tank never use treated water on them though! Makes brown spots, just use untreated spring water for misting the tank and watering plants.
Have you ever given him a lukewarm honey bath?