Thank you, Steven.
Now when we see discoloration and odor change of a cat's urine, we do have a few different issues to consider. Provided he hasn't had access to some strangely pigmented food stuffs (very unlikely for this species), then the most common reason in an cat Sasha's age would be a bacterial bladder infection (+/- kidney infection). Often the bacterial presence in the urine leads to changes in color (sometimes the urine also seems cloudy or flocculant) and to the odor (the product of the bacteria altering the urine componsition). Cats with bladder infections may also show belly discomfort, increased urinary frequency (sometimes passing only small volumes), increased straining to urinate, going in odd places, and increased grooming of their irritated genitals.
That said, your mention of a very distinct bright discoloration (obviously I cannot see the urine but I am thinking you are seeing a almost highlighter orange type urine that would be so color intense that it may stain in contact surfaces), along with his sickness, appetite decline, and belly tenderness last night does make me a wee bit concerned that we could seeing something more sinister. Specifically, we can see bright orange/yellow discoloration in cat's urine with the appearance of bilirubin in the urine. Bilirubin is a bile pigment that is produced by the liver. If the liver is in distress (with bacterial or viral infection, toxic damage, obstructions in the gall bladder, tumors, etc) or if a cat is suffering from an anemia due to red blood cell rupture, we can see bilirubin leak into the blood and then into the urine. In severe cases, cats may start to show yellow staining of the skin (which is why I noted having a peek at his gums, in his ears and the whites of his eyes --though we'd expect to see urine changes first).
In this situation, with two different concerns for Sasha, I must say that it would be prudent to have him checked by his vet today even if he is feeling a bit better. Ideally or if you wanted to do so before having him seen, we'd want to collect a urine sample and submit it to your vet to analyze. Often we can obtain a ‘donation’ if the kitty is left in a non-carpeted room with an empty litter box, or if a sample is collected from the non-carpeted floor. The vet will be able to analyze it and determine if there is anything abnormal. They will be able to appreciate changes to the urine's white blood cell content (a marker of infection, which would let us know if this is just a bladder infection), bilirubin (that marker of liver disease or blood cell hemolysis --and just to note ANY bilirubin in a cat's urine is abnormal and a red flag that we need to check for anemia or liver issues), specific gravity (to tell is the urine is as concentrated as it should be - an issue for some liver diseases and for kidney troubles) and the presence of glucose/ketones (markers of diabetes). Furthermore, the sample can be analysed under the microscope for white cells, bacteria, bilirubin crystals, and other signs of infection. Overall, this is quite a non-invasive means of determining the root for these urinary signs you have seen. Depending on their findings, it may just be a case of antibiotics to treat a bladder infection. But if the liver values are abnormal or he is pale/anemic, then it would be prudent to have his vet check bloods and examine him to get to the bottom of these signs. Because if there is a problem in his liver or something rupturing his red blood cells, then quick diagnosis and treatment will give him the best chance of settling this.
Overall, we do have to have a few concerns about Sasha's urinary signs. As I said before, bladder infections tend to top the list when we see changes to urine but with the discoloration and his other signs I would be concerned that we may be seeing a start to a liver based issue. Therefore, I'd strongly advise being proactive and at least getting a urine sample checked today. Depending on the findings of this (or if you do have him checked), your vet can give you an idea of what is affecting Sasha and the next step to diagnose or treat this issue for him.
I hope this information is helpful.
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