The blood you are seeing in the urine is likely related to inflammation of the bladder lining. The fact that xrays, and urinalysis are all clear does make a sterile cystitis likely. This is can occur when the bladder lining is inflammed and in some cases there is no obvious cause. This may respond to NSAIDs (non steroidal antiinflammatory drugs) or steroids (may be a little excessive) to reduce the inflammation in the bladder.
It may be worth discussing a bladder ultrasound with your vet. This may reveal stones that are not evident on xrays or urinalysis, bladder tumor (not likely at this age), or sludge (this is sediment in the bladder that can irritate things, but may not show up on xrays or urinalysis) in the bladder.
If this ends up being a case of cystits, you may find that it could clear up on its own. However, if you are noting an increase in frequency of urinations or straining to urinate, then I would discuss being more aggressive with your vet by looking into some of the things I have mentioned above. I hope this helps and gives you direction.
He did get a shot of something the first time the vet said would calm the bladder. He isn't worse and is actually better than a couple of weeks ago. He will have a big normal looking "wee" and then he will have a few tiny bloody ones.
I've already spent $400 on this and ultra sound sounds like another $200. When you say NSAID can I give him a baby aspirin?
Also, he mentioned low ash dog food? How is that related? He eats Natural Balance Lamb & rice now.
Aspirin in a human NSAID but can cause some clotting issues. This could actually make for more blood in the urine. The drugs approved in dogs would be a better choice as they will not have the same anticoagulant effect.
Unfortunately, the ultrasound could be rather pricey, but that would be the next diagnostic test.
Your vet mentioned low ash food there can be a correlation with this and lower urinary tract disease. While this is rather common in cats, it can be seen once in a while with dogs. Your vet will have several urinary specific diets that may help based on what was found on urinalysis. In some cases, a diet change can help. Since I have some clients that are not happy about using a prescription food (I like these foods, but in practice I have also learned to pick my battles so if clients do not like these, for whatever reason, I will try other options), I will often recommend a holistic brand such as Pinnacle. Here is there website with more.
While I see great succes with some of my dogs with food allergies, there could definitely be a benefit with the urinary tract as well especially if the prescription foods are not an option. I hope this helps.
The concern to watch for, is an inability to pee. There is a stone called a urate stone which may not be evident on xrays. While these typically occur in dalmations or dogs with a congenital liver issue (not likely with your dog), it could cause irritation to the bladder and urinary obstruction. For now, I would discuss some of the medical options I discusses. One other option is a product called Cosequin. This was initially produced to help arthritic dogs, but a benefit to the bladder lining was discovered in some dogs. While results are inconsistent it may be worth asking your vet about it.
I hope this helps.