Welcome to Justanswer! I am Dr. Altman and happy to assist you both today!
Unfortunately starting antibiotics before a urinalysis is run will effect results and treatment options. In addition, if a urine culture is run it can deter finding the bacteria that is causing his symptoms
As an alternative, ideally until you are able to get to your veterinarian, please increase water intake. You can do this by supplementing the dry food with water and flavoring the water (maple syrup or no salt broth for example) as well. Increasing the water intake will help "flush" out the bladder and reduce the pain associated with the possible infection.
Collecting a first morning sample in a tupperware container and refrigerating the sample if more than an hour old to have your vet evaluate the sample will help determine the cause of the blood in the urine.
Your vet will run a urinalysis, potentially do a urine culture to look for bacteria if antibiotics are not started tonight, an X-ray to rule out a bladder stone, and bloodwork to ensure there is not a metabolic cause or kidney issues causing the symptoms
Diagnosing the issue will help determine how best to treat the blood in the urine to get your pet comfortable swiftly
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