A dog that can’t urinate is almost always facing a physical blockage, a nerve problem, or inflammation somewhere in the urinary tract. This is a genuine emergency. When urine backs up, toxins build in the bloodstream and the bladder can rupture, so a dog that hasn’t peed in 12 or more hours, or is straining repeatedly without producing urine, needs veterinary attention the same day.
Bladder Stones Are the Most Common Cause
Urinary tract stones are the number one reason dogs develop a full urethral blockage. Minerals crystallize inside the bladder, and as the stones move toward the exit, they can lodge in the urethra and completely block urine flow. Male dogs are especially vulnerable because the male urethra narrows as it passes through a small bone in the penis called the os penis. Stones that would pass easily in a female dog get stuck at that bottleneck in males.
The type of stone depends partly on breed. Small breeds like Miniature Schnauzers, Chihuahuas, Bichon Frises, Yorkshire Terriers, Shih Tzus, and Lhasa Apsos are more commonly affected by calcium oxalate stones. Struvite stones, which are extremely common in cats, rarely form on their own in dogs. When they do appear in dogs, they’re almost always linked to a urinary tract infection that changes the chemistry of the urine. Cystine stones show up mostly in young, intact males, and because their formation is partly driven by male hormones, neutering can help prevent recurrence.
Prostate Problems in Unneutered Males
If your dog is an intact (not neutered) male, his prostate could be the problem. As unneutered male dogs age, hormones cause the prostate gland to enlarge, a condition called benign prostatic hyperplasia. The prostate sits right below the bladder and wraps around the urethra, so when it swells enough, it physically compresses the tube that carries urine out of the body. Dogs with this issue often strain to urinate and defecate, produce a thin or intermittent stream, or dribble urine without fully emptying.
Neutering resolves most cases of benign prostate enlargement because it removes the hormonal signal driving the growth. The prostate typically shrinks within weeks after the procedure.
Tumors That Block Urine Flow
Bladder cancer in dogs most often takes the form of a tumor called urothelial carcinoma. These tumors tend to grow at the trigone, the junction where the bladder connects to the urethra, which is the worst possible location for maintaining urine flow. As the tumor grows, it narrows or blocks the opening, making it progressively harder for the dog to urinate. Dogs with trigone tumors may strain, pass small amounts of bloody urine, or eventually stop being able to urinate altogether.
Tumors can also develop on or near the penis itself, creating external compression of the urethra. Any unexplained, worsening difficulty urinating in a middle-aged or older dog should raise concern about cancer, especially if antibiotics and dietary changes haven’t helped.
Spinal Cord and Nerve Damage
Urination requires coordination between the bladder muscle, which squeezes, and the sphincter, which relaxes to let urine out. The spinal cord manages that coordination. When a disc herniates, a fracture occurs, or a tumor compresses the spinal cord, the signals between the brain and bladder get disrupted. Depending on where the damage is, the result can be a bladder that fills but can’t contract, a sphincter that won’t relax, or both.
After a severe spinal cord injury in the mid-back region, dogs typically enter a phase of complete urinary retention that can last two to six weeks before any reflex bladder activity returns. During that time, the bladder must be manually emptied several times a day by a caregiver or veterinarian using a catheter or manual expression. Injuries lower on the spine, near the tailbone, can leave the bladder muscle permanently flaccid while the sphincter stays tight, creating a bladder that overfills and distends painfully.
If your dog suddenly can’t urinate and also has weakness or dragging in the hind legs, a spinal problem is likely. This combination is a surgical emergency.
Other Causes Worth Knowing
Not every case involves stones, tumors, or nerve damage. Scar tissue from a previous surgery, catheterization, or infection can narrow the urethra enough to partially or fully block it. Severe urinary tract infections cause enough swelling and inflammation to make urination painful and difficult, though complete blockage from infection alone is uncommon. Blood clots inside the bladder, sometimes from trauma or a bleeding disorder, can also plug the urethral opening.
A fractured os penis (the bone inside the male dog’s penis) from a pelvic injury can crush or deform the urethra. This is rare but worth mentioning because it’s easy to miss if the vet focuses only on the pelvis after a car accident or fall.
How Your Vet Figures Out the Cause
Your vet will start by feeling your dog’s abdomen. A bladder that’s full and firm like a water balloon tells them urine is being produced but can’t get out, which points to a blockage. If the bladder is small or empty, the issue might be that the kidneys aren’t producing urine at all, which is a different and equally serious problem.
X-rays can reveal most types of bladder and urethral stones, since many stone types show up clearly on film. Ultrasound picks up stones that don’t appear on X-rays, along with tumors, blood clots, and structural abnormalities inside the bladder. If a blockage is confirmed, the vet will likely pass a urinary catheter to relieve the pressure immediately, then move on to figuring out the underlying cause.
Blood work is important because a blocked dog’s kidneys may already be struggling. When urine can’t leave the body, waste products like potassium build up in the blood, and dangerously high potassium can cause fatal heart rhythm problems. This is the main reason urinary blockage kills dogs if left untreated.
What Treatment and Costs Look Like
The first priority is restoring urine flow. That usually means sedation and catheter placement to drain the bladder. If a stone is lodged in the urethra, the vet may be able to flush it back into the bladder with a saline solution (called retrograde flushing), then plan for surgical removal. Some small stones can be dissolved over weeks with a special diet, but a dog in active blockage needs mechanical relief first.
Emergency visits for urinary blockage tend to be expensive. Exam fees alone run $100 to $300, higher on nights and weekends. Bloodwork adds $150 to $300. Catheterization, hospitalization for monitoring, IV fluids, and medications can push the total well past $1,500. If surgery is needed to remove stones or a tumor, costs climb further. The total depends heavily on your location, the underlying cause, and how long your dog needs to stay hospitalized.
Signs That Suggest a Partial Blockage
Not every case starts as a total inability to urinate. Many dogs go through days or weeks of worsening partial blockage before owners realize something serious is happening. Watch for these signs:
- Straining for a long time with only drops or a thin stream coming out
- Frequent attempts to urinate with little result
- Blood in the urine, which can appear pink, red, or brownish
- Licking the genital area more than usual
- Crying or whimpering while trying to urinate
- A swollen, tense abdomen that’s painful when touched
A healthy dog produces roughly 20 to 100 milliliters of urine per kilogram of body weight per day. For a 20-pound dog, that’s about 180 to 900 mL daily. If your dog is making noticeably less than that, or nothing at all, don’t wait to see if it resolves on its own. Urinary blockage can progress from uncomfortable to life-threatening within 24 to 48 hours.