Pyelonephritis (inflammation of the kidney) in dogs: causes, symptoms and treatment


Pyelonephritis is an inflammation of the kidney. In most cases, it is caused by an ascending bacterial infection from the lower urinary tract (urinary bladder) to the kidney. The predisposition to infections can be increased by factors such as congenital anomalies, metabolic disorders or systemic immunosuppression. However, pyelonephritis can arise even in the absence of underlying pathologies.

The clinical signs associated with pyelonephritis can be mild or go unnoticed, although this condition, if left untreated, can lead to the onset of kidney failure, sepsis (generalized infection throughout the body) and possibly death. In general, depending on each specific case, diagnostic and therapeutic procedures formulated on an expressly individual basis are recommended.

Since many pathologies or disorders can present themselves in a similar way, it is necessary to differentiate them from pyelonephritis. They include:

  • Urolithiasis (calculations) of the urinary tract
  • Chronic renal failure
  • Bacterial prostatitis (inflammation of the prostate)
  • Metritis (inflammation of the uterus)
  • Other causes of fever and abdominal pain, such as pancreatitis (inflammation of the pancreas) or peritonitis (inflammation of the abdominal cavity)
  • Other causes of increased thirst and polyuria (increased amount of urine emitted), such as hyperadrenocorticism (Cushing’s syndrome) diabetes mellitus, kidney disease and liver disease.

Signs and symptoms

  • Excessive water intake and excessive urination
  • Abdominal or back pain
  • Stress when urinating
  • Presence of blood in the urine



To diagnose pyelonephritis permanently and to exclude other pathological processes that can cause similar symptoms, certain diagnostic tests are required. Full history, description of clinical signs and thorough physical examination are important for achieving a presumptive diagnosis of pyelonephritis. In addition, the following exams are recommended:

  • Complete blood count test. Results may have values ​​within normal limits, but a high white blood cell count may be present.
  • Biochemical profile. The results may present values ​​within normal limits, but may reveal elevations of renal enzymes or electrolyte disturbances.
  • Urine analysis. It can reveal the presence of blood, white blood cells, proteins or bacteria in the urine. The absence of one or all of these elements does not exclude pyelonephritis.
  • Urine culture. It is performed to confirm the presence of a urinary tract infection. However, in some cases of pyelonephritis, the outcome can be negative.
  • Abdominal radiographs. They are an important part of the basic diagnostic process. Although the outcomes may be within normal limits, abdominal radiographs may reveal changes in kidney size, urinary stones or help rule out other pathologies and causes of the patient’s clinical signs.
  • Abdominal ultrasound. It is recommended in most cases where pyelonephritis is suspected. It is useful for evaluating the kidney and for differentiating a possible lower urinary tract infection from an upper urinary tract infection. In the presence of pyelonephritis, characteristic changes in the renal pelvis can be observed. In acute cases, the kidneys may appear enlarged, while in chronic cases they may appear small. Furthermore, ultrasound is useful for assessing the presence of stones in the urinary tract. It is a non-invasive procedure that often requires the expertise of a specialist.

To rule out or diagnose concomitant conditions, the veterinarian may recommend further tests. These are not always necessary and are selected on an individual basis according to each specific case. These exams include:

  • Excretory Urography. It is a radiographic study with contrast medium (administered intravenously) of the upper urinary tract (kidneys and ureters) and is useful for documenting pyelonephritis. The excretory urography also helps to identify the presence of stones in the urinary tract and other anomalies, such as ectopic ureters. Urethral ectopia is a congenital anomaly in which the ureter (excretory canal of the kidney that brings urine to the bladder) joins the bladder in an improper anatomical position, causing a set of clinical signs, such as urinary incontinence and recurrent infections.
  • Bacterial culture of a sample taken from the renal pelvis. By means of an ultrasound-guided procedure, this examination can be particularly important in the patient who presents a negative result following a urine culture performed on a sample collected from the urinary bladder.
  • Kidney biopsy. In some cases, this invasive procedure can be helpful in diagnosing pyelonephritis and, in certain cases, may require exploratory surgery.


If the patient is stable, the treatment can be carried out at home, provided that the animal is carefully monitored. Most dogs, after adequate therapy, can fully recover. In more chronic cases, the response to therapy may take longer and sometimes the response may be poor. It is essential that the dog owner scrupulously follow all the recommendations suggested by the veterinarian. If doubts or concerns arise during the treatment protocol, it is good to contact the veterinarian immediately.

  • In order for the treatment to be effective, it is essential to correct any predisposing factors, including ectopic ureters, urolithiasis or prostatitis.
  • Antibiotic therapy is the most important part of the treatment. Antibiotics will be selected based on the results of the bacterial culture and the bacterial sensitivity test of urine or kidney tissue. It is important for the owner to administer all the prescribed drugs to the dog following the procedures suggested by the veterinarian. Typically, the duration of the treatment protocol is at least 4-6 weeks.
  • In dogs with concomitant renal insufficiency or urolithiasis, changes in the diet are recommended.
  • In some cases of pyelonephritis, hospitalization, intravenous fluid therapy and administration of antibiotics may be necessary.
  • In cases of pyelonephritis associated or secondary to urinary stones, surgical intervention may be necessary.

Follow-up can be critical, especially the dog does not improve quickly. Pyelonephritis, if not resolved, can lead to the onset of kidney failure. Therefore, diagnostic follow-up is important for documenting the resolution of the condition.

Urine culture and urinalysis will have to be repeated after 7-10 days about the start of treatment and 1-2 weeks after the end of therapy. It is important to carry out urine culture every 2-3 months until 3 negative cultures are obtained. If the outcome is positive, an additional course of antibiotics is generally recommended, often of longer duration than the previous one. In some dogs, despite adequate and repeated courses of antibiotics, the infection may persist.

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