Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am very sorry that your fellow has blood in his urine, less of an appetite and is lethargic.
There are many reasons to have blood in the urine or bleeding from the penis/prepuce.
We often think of an infection but also crystals or stones in the urinary tract, masses on the penis or prepuce or in the urinary or reproductive tract or clotting disorders are possible causes. If he is an un-neutered male prostatic cysts or an abscess or a prostatic tumor are possible causes as well.
Are his gums and tongue white, pale pink or bubble gum pink? If they are nice and pink then he likely hasn't lost enough blood to make him anemic and that is a good sign.
Is he bleeding only when he passes urine (is he constantly straining and dribbling urine) or does the bleeding seem independent of passing urine?
If the bleeding is when he passes urine then concerns would be a genitourinary tract infection, crystals or stones in his urinary tract, a clotting abnormality or a mass in his urinary or reproductive tract.
If the bleeding is independent of him passing urine the concerns would be trauma to his penis, a mass in his prostate, prepuce or on his penis, or a clotting abnormality.
You can try to gently retract his prepuce over his penis to look for a mass or cut either in his prepuce or on his penis. If he hasn't been neutered and if his penis and prepuce look normal he may have prostatic disease. If you can see a mass or a cut on his penis or prepuce then a cold compress on it, followed by gently it patting dry and then applying some corn starch or flour to help form a clot may stop the bleeding. Then he should see his regular veterinarian for treatment tomorrow.
If he doesn't have a visible mass or cut and he were my patient I'd start with a urinalysis with culture and radiographs of his abdomen to look at his kidneys and bladder for signs of stones and the size and shape of his prostate. We may need an abdominal ultrasound to look at his kidneys, bladder and prostate. If he had pale gums signifying significant blood loss then I would want to check his clotting function too.
Is he running a fever (rectal temperature greater than 103F)? If so a kidney or prostatic infection are good possibilities.
If money was very tight and there were signs of infection on the urinalysis then an antibiotic prescription for 10 to 14 days would be reasonable to start.
If I saw lots of crystals or abnormal looking cells on the urinalysis I'd warn the owner that things may be more serious.
And I'd recommend a recheck of his urine at the end of the antibiotic therapy. If there was still blood then radiographs or an ultrasound of his bladder/kidneys is needed.
If this is a prostatic infection I highly recommend that he be neutered once he feels a little better. When they are neutered and the effects of high testosterone are gone the prostate shrinks which helps prevent infections.
All you can do for him at home is encourage fluid intake to flush out his urinary tract. Add water or low salt beef or chicken broth to his food or feed him canned food to encourage eating and increase his fluid intake.
Give him ice cubes. Offer him fresh water frequently.
And make sure he gets out frequently to urinate.
If he is straining but unable to pass urine, is vomiting, runs a fever (more than 103F rectally), has a tense, painful abdomen with gentle pressure, or his gums become very pale it is time for emergency veterinary care.
Let me know if you have any further questions.