Usually, a blockage will happen unilaterally (on one side). If a blockage develops in both ureters, both kidneys will be affected and complete renal failure will begin to develop. This is a life-threatening circumstance requiring immediate veterinary attention. When urine is trapped in a kidney, bacteria begin to grow, which leads to infection. This can also hinder kidney function and has the potential to spread to other organs. This issue is more common in young male cats and elderly cats, but it can develop in cats of any age or sex. 

The kidneys drain liquid metabolic waste (urine) that has been removed from the bloodstream down to the bladder through narrow tubes called “ureters”. Because these ureters are so narrow, they can become blocked or obstructed by many different causes. When this happens, urine is unable to leave the kidneys, and as the kidneys continue functioning, they overfill with liquid. If a blockage has existed for some time, the affected kidney will enlarge and begin to lose function. This is referred to as hydronephrosis.

In unilateral cases of hydronephrosis in cats, symptoms may be too mild to notice for the average owner. After the issue has existed for a period of time, the kidney will begin to swell to the point of visibility from outside the abdomen. If the hydronephrosis is bilateral, multiple symptoms will show in a short timeframe. Symptoms to watch for include:

Any health issue that causes the development of an obstruction can lead to hydronephrosis. Issues that cause extreme renal or pelvic swelling can also cause the ureters to be pushed shut from inflammation. Known causes include: 

If you suspect your cat is showing one or more of the listed symptoms of hydronephrosis, bring it to a veterinary clinic immediately. Once there you will be asked to provide the cat’s full medical history. The veterinarian will perform a complete physical examination, palpating the abdomen to determine if one of the kidneys is noticeably larger than the other. If the veterinarian notes that symptom onset is rapid, emergency procedures to stabilize the cat may be started before a complete diagnosis has been made.

Full blood work will be run including a complete blood count and a biochemical profile to determine the levels of potassium in the blood. Urinalysis may be useful to monitor the level of kidney function still present. A bacterial urine culture can help identify any harmful bacteria that may be causing infection in the affected kidney. X-rays of the abdomen can help rule out other kidney problems and locate the area of the blockage. Excretory urography using dye may be performed to get a better visual on the upper urinary tract to see the blockage more clearly. If a low heart rate is present, electrocardiogram tests may also be run.

Appropriate treatment will depend on the issue that has caused the blockage and the severity of the health condition. Bilateral hydronephrosis requires emergency care to save the cat’s life. In mild unilateral cases, sometimes a blockage will pass on its own.

IV Fluid Administration Many cats who suffer from hydronephrosis are dehydrated to some degree. Intravenous administration of saline and electrolytes can help restore stability to a severely dehydrated cat. The fluids should be given slowly, with insulin, dextrose, and potassium being added in some instances. Hospitalization is required for IV treatment.

In severe cases of hydronephrosis, surgery may be required to remove tumors causing the blockage. Because the ureters in a cat are so small, often a ureteronephrectomy (removal of the affected ureter and kidney) is performed instead. This procedure may also be done if the affected kidney has lost all or most of its function. Prior to this surgery being completed, the unaffected kidney must be tested (often with a biopsy) to ensure that it is healthy enough to take on the workload of the nonfunctional kidney. General anesthesia is required for the procedure. 

If a bacterial infection has been identified in the urinary tract, the corresponding antibiotic will be prescribed. Post surgery, antibiotics will often be prescribed as a preventative measure to keep infections from developing in the incision. These prescriptions generally last from one to four weeks. 

In mild cases, your veterinarian may create a diet specific to your cat’s needs to help ease kidney trouble and prevent the possible growth of urinary stones. 

If your cat has undergone surgery, be sure to follow all at-home care instructions closely. Monitor the incision site daily to look for early signs of infection including redness or swelling. Limit activity during the recovery period. Administer all painkillers and antibiotics as prescribed. Maintain a strict diet as advised by your veterinarian to help prevent urinary stones from forming. Provide fresh water to your cat multiple times a day to ensure it is hydrated. 

Follow-up appointments at the veterinary clinic will be needed to monitor your cat's recovery and to ensure that surgery has been performed correctly. If hydronephrosis is detected early (up to four weeks post obstruction), recovery is likely. If diagnosis is late, kidney damage may be permanent. Bilateral hydronephrosis needs to be identified and treated within the first 24 hours. Failure to do so may result in the cat’s death.