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Kidney Infection: Pyelonephritis

Understanding Your Pet's Medical Diagnosis

What is pyelonephritis?

Pyelonephritis is the medical term for inflammation of the kidneys that involves the firm portion of the kidneys and the renal pelvis. "Pyelo-" refers to the renal pelvis, the area where urine collects in the kidney as it moves toward the ureter (the tube from the kidney to the bladder). Nephritis is the general term for inflammation of the kidneys. Pyelonephritis is a bacterial infection of the kidneys and ureters. It also is called an "upper urinary tract infection."

What causes pyelonephritis?

Pyelonephritis usually is caused by bacterial infection. Pyelonephritis frequently is accompanied by lower urinary tract infection (bladder and urethra). The urethra is the tube that leads from the bladder to outside the body. Pyelonephritis usually occurs when bacteria travel from the bladder to the ureters and kidneys. The most common bacteria are Escherichia coli and Staphylococcus.

What are signs of pyelonephritis?

Signs of pyelonephritis vary. Many pets have no signs or only have signs associated with lower urinary tract infection. Signs of lower urinary tract infection include difficulty urinating (dysuria), frequent urination (pollakiuria), blood in the urine (hematuria), and discolored urine that has a foul odor. Other signs that may be seen in cases of pyelonephritis include fever, excessive urination (polyuria), excessive thirst (polydipsia), or abdominal pain.

How is pyelonephritis diagnosed?

Any pet with urinary tract infection potentially could have pyelonephritis. Laboratory tests include complete blood counts (CBCs) and blood chemistries, but these often are normal. If the pyelonephritis has damaged the kidneys and the animal is in kidney failure, the blood chemistry results will be abnormal. The animal will have high concentrations of blood urea nitrogen (BUN) and creatinine. Urinalysis will reveal abnormalities (such as blood, pus, or bacteria) in the urine. Multiple bacterial urine cultures may be needed.

The best method for differentiating between upper and lower urinary tract infection is ultrasound (visualization of deep tissues by recording ultrasonic waves) or excretory urography (a special contrast radiograph [X-ray]). These two procedures enable the veterinarian to visualize the entire urinary tract. A definite diagnosis also requires urine culture directly from the kidney or kidney biopsy (removal and examination of kidney tissue). A tissue specimen may be retrieved by inserting a needle through the skin and into the kidney and drawing some cells into a syringe (needle biopsy). However, a more reliable method is a surgical kidney biopsy where kidney tissue is obtained during abdominal surgery because pyelonephritis can be missed by needle biopsy. Surgery needs to be considered carefully and performed only when necessary.

How is pyelonephritis treated?

Pyelonephritis is treated with antibiotics. The antibiotic should be chosen based on urine bacterial cultures, if possible. Oral antibiotics should be given for 4 to 6 weeks. Follow-up examinations and repeat urine cultures and urinalysis are important because unresolved pyelonephritis may lead to chronic renal failure.

What is the prognosis for animals with pyelonephritis?

The prognosis (outcome) for animals with pyelonephritis is fair to good unless the animal has an underlying cause of urinary tract infection, such as obstruction or cancer. Severe and long-term infections of the kidney may be difficult to cure because antibiotics often do not penetrate kidney tissue in high enough concentrations to ensure eradication of the infection.


The majority of the information in this page is has been taken from VetMedCenter.com. For further information about this useful source of informtion follow the link or look, on the internet, at www.vetmedcenter.com.

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