Urinary Obstruction in Dogs

By: Christine New, DVM

TVMA Member
Dallas, Texas

Published January 2015

A pet with a urinary obstruction is unable to urinate normally. Urinary obstructions may be partial or complete, and the signs you may notice at home can range from subtle signs like taking longer than normal to urinate or urinating small amounts in several spots to severe signs such as collapse. Urinary obstruction can look similar to a urinary tract infection and can be difficult for pet owners to distinguish. If you feel your dog is not urinating normally, is in pain or crying out when urinating, a prompt veterinary exam is always needed!

How Does the Urinary System Work?

Just like in humans, your pet’s kidneys make urine and send the urine to the bladder via two tubes called ureters, which connect each kidney to the bladder. In a normal dog, urine is emptied from the bladder, leaving the body through a single tube called the urethra. The urethra starts at the bladder and provides the exit path out of the body. The most common areas for problems resulting in a urinary obstruction are the urinary bladder and the urethra, both in male and female dogs.

What are the Signs of Urinary Obstruction in Pets?

Signs of a urinary obstruction include crying when urinating, asking to go outside more frequently, posturing to urinate with no urine coming out, repeatedly posturing to urinate and only small amounts of urine are seen, bloody urine, vomiting, lethargy or lack of appetite. The composition of urine is waste products that are meant to be excreted from your pet’s body. If your pet is unable to urinate, these waste products can quickly reach toxic levels that can become dangerous or even life-threatening to your pet and will quickly make your pet ill.

What Causes Urinary Obstructions?

The most common causes of urinary obstructions in male and female dogs are bladder stones, urethral stones and cancer. Additionally, disease of the prostate gland can cause urinary obstruction in males only, as females do not have a prostate gland. Also, spinal cord injuries can render a pet unable to urinate.

Both male and female dogs are affected by urinary obstructions, although usually male dogs become more ill as they tend to form a complete obstruction. The reason male dogs are more seriously affected is because the urethra is longer in males than in females and narrows considerably as it approaches the penis. This is especially concerning when dealing with bladder and/or urethral stones. Stones are less likely to become lodged in a female urethra; the urethra in females is shorter and wider so a stone can more easily leave the body in the urine, although the process is still painful. In both sexes, almost all stones form in the bladder; large stones that are too small to leave the bladder through the urethra tend to remain in the bladder, resulting in pain, infection and potentially partial obstructions. Small stones or pieces of the larger stones can pass out of the bladder and become lodged in the urethra.

Tumors of the bladder and urethra also cause an obstruction when they grow large enough to stop the passage of urine. Signs seen are identical to what is seen with an obstruction caused by stones, and bloody urine is very common.

In male dogs, the urethra passes through the prostate gland, which forms a complete circle around the urethra. Enlargement of the prostate gland (prostamegaly) is extremely common in older dogs that have not been neutered. Prostamegaly also occurs in older neutered dogs but with less frequency and less severity. Severe prostamegaly closes off the urethra as it passes through the prostate, just after exiting the bladder, resulting most commonly in a partial urinary obstruction. Severe prostate enlargement can cause complete urinary obstruction. Prostamegaly can also be caused by a tumor of the prostate. Signs you may see at home are very similar to other causes of urinary obstruction. Some inflammatory prostate diseases can be treated by neutering an intact male.

How Does Your Veterinarian Diagnose and Treat Urinary Obstructions?

If your pet is unable to urinate, the urinary bladder will be very large and painful when examined by your veterinarian. Your veterinarian will complete X-rays to confirm a urinary obstruction and also to look for stones within the urinary bladder and urethra. Sometimes cancer can be seen on an X-ray, but typically an ultrasound exam is a better modality for identifying a tumor of the bladder or urethra. Your veterinarian will also collect a blood sample to test your pet’s electrolytes and kidney values. Specifically, the electrolyte potassium can become dangerously high if your pet cannot urinate; a very high potassium level can cause your pet’s heart to beat abnormally. Elevated kidney values may indicate kidney damage; whether the damage is permanent or transient can only be determined over the course of several days of treatment. The initial kidney values are almost always elevated with urinary obstruction, but unless your pet has pre-existing kidney disease or the obstruction was present for several days, the insult to the kidneys is usually transient and resolves within the first 48 hours of treatment. If your pet’s potassium level is high, additional treatment may be needed before your veterinarian can safely anesthetize your pet to relieve the obstruction. A urine sample will be analyzed for crystals, cancer cells, protein and infection.

In order to relive the urinary obstruction, a urinary catheter must be placed. To do this, your pet will be anesthetized briefly. A catheter will be inserted into the urethra and run all the way into the urinary bladder, sutured in place and secured to a collection bag that will hang outside of your pet’s hospital kennel. Your pet will now urinate out this catheter and into the bag. Typically, the urinary catheter is left in place for one to four days, meaning your pet will remain in the hospital during this time. Your pet will also be on IV fluids, pain medication and antibiotics. Bloodwork will be completed at least daily to monitor kidney values. Initially, blood testing may be needed to monitor electrolyte values every few hours until values are normal. As mentioned above, very high potassium values can be very dangerous, so your veterinarian will want to return the potassium level to a normal range as quickly as possible, and sometimes additional medications other than IV fluids may be indicated to achieve this.

Depending on the cause of the obstruction, surgery may be needed once the kidney and electrolyte values are normal and your pet is stable. Bladder and urethral tumors may require surgery as do male dogs with stones in the urethra or bladder typically. Female dogs with stones may be candidates to diet dissolution. Some stones may be dissolved by a special prescription diets, but this process may take months and re-obstruction can occur. Ask your veterinarian if your pet is a candidate for prescription diets meant to dissolve and prevent recurrence of stones. If you have a male dog and prostatic disease is the cause of the urinary obstruction, your veterinarian will likely recommend your dog be neutered immediately to encourage the prostate to decrease in size.

Regardless of the cause, urinary obstruction is a serious condition, and veterinary care should not be delayed. If you feel your pet is not urinating normally, always contact your family veterinarian or local emergency clinic for an immediate exam.

Dr. Christine New practices veterinary medicine at the Hillside Veterinary Clinic in Dallas.