– An acute or chronic infection and inflammation of the kidney or renal pelvis. (Also see Urinary Tract Infection.)

Causes and Incidence

Acute pyelonephritis is caused by a bacterial invasion that moves from the urethra to the bladder to the ureters to the kidney. The infecting bacteria are commonly normal intestinal and fecal flora that grow readily in urine. Individuals with a condition that interferes with the dynamics of normal urine flow are at greater risk. This includes those with underlying obstructions (strictures, calculi, tumors, prostatic hypertrophy), neurogenic bladder, vesicourethral reflux, diabetes, or renal disease; those who are sexually active or pregnant; and those undergoing medical or surgical procedures such as catheterization or cystoscopy. Women are more susceptible than men because of the anatomic construction of the female urinary system. The annual incidence of pyelonephritis in the United States is 16 in 100,000; the annual nosocomial incidence rises to 73 in 100,000. Chronic pyelonephritis most typically occurs as a result of repeated acute episodes but may also be caused by metastatic disease.

Disease Process

Bacteria ascend the urinary tract and colonize one or both kidneys. The kidney enlarges as the inflammatory process is activated, and parenchymal tissue is destroyed. Chronic inflammatory cells appear within a few days, and medullary abscesses and papillary tissue necrosis occur. Patchy spots of infection develop and spread to the pelvic and calyceal epithelia and the cortex. If the process becomes chronic, atrophy, calyceal deformity, and parenchymal scarring occur.


The onset is fairly rapid and is characterized by dull, constant flank pain, chills, and fever. Concomitant signs of a lower urinary tract infection (e.g., urinary frequency, dysuria) occur in about one third of individuals.

Potential Complications

The most common complication of acute disease is septic shock or chronic pyelonephritis (or both). With chronic disease there is a 2% to 3% chance of developing end-stage renal failure.

Diagnostic Tests

Presenting clinical symptoms are confirmed by urinalysis, which reveals antibody-coated bacteria, bacteriuria, WBC casts, and pyuria; a complete blood count shows an increase in WBCs. Renal function studies may assist in the diagnosis of chronic disease.


Correction of underlying obstructions.

Oral or parenteral antiinfective drugs to combat infection; continuous suppression antiinfective therapy may be used to treat recurrent or chronic infection; antipyretics for fever.

Increased fluid intake; urine cultures to track effectiveness of antiinfective drugs; instruction in preventing infection (cleansing perineum, proper wiping technique, adequate fluid intake, cleansing after sexual activity).