Hi there. My name is ***** ***** I'm happy to help you with your question today.
I'm sorry to hear that your dog isn't feeling well. Unfortunately, bleeding during urination can be caused by many things that range from the rather benign (like a urinary tract infection) to the more dangerous (such as bladder cancer). In addition, there are issues like bladder stones or kidney disease that can present with bloody urine.
Stones are caused by things such as minerals in the urine, bacteria, certain medications, an excess of Vitamin C in the diet or even their diet (which can affect the pH of the urine). There are some breeds that are more prone to stones than others (such Poodles, Yorkies Shih Tzus and Schnauzers) although any breed can get them (I have a Maltipoo who has had them twice!). Usually a course of antibiotics and a diet change to a prescription diet takes care of the problem.
Kidney disease can happen in any breed and unfortunately, at most any age. The contributing factors can include dehydration, cardiac issues, tumors, blood loss from traumas and both infections and ingestion of toxins. Even some medications can impair kidney function and lead to kidney disease. Generally this is treated with supportive care to keep the dog comfortable and to help improve kidney function.
Bladder cancer generally affects middle-aged or older dogs. Although not nearly as common as some of the other possibilities, I wanted to mention this as well since it is ofen over-looked as a cause of bloody urine especially if the dog is otherwise healthy and hasn't had any long-term issues.
Urinary tract infections (also known as UTIs) are the number one most common cause for bloody urine in dogs. The infection can be located anywhere in the urinary tract from the bladder to the kidneys and in unneutered male dogs, even in the prostate. Certain medications and underlying health problems such as diabetes or viral infections can also lead to UTIs.
The important thing is to have your pup seen by a vet as soon as possible for evaluation of the blood in the urine. Bloody urine is never 'normal' and can get worse if left untreated. Your vet will likely want to run a urinalysis, so if you can catch urine from your dog before going (you can catch it up to 24 hours before your appointment, just keep it in a clean, closed container in your fridge. Do not leave it out of the fridge as that will cause bacteria to grow in the urine and may give you false positives). Hopefully it'll end up being nothing too severe, but early intervention is the key.
I hope this helps!!