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Acute Pyelonephritis

Acute pyelonephritis (also called acute infective tubulointerstitial nephritis) is one of the most common renal diseases. In this disorder, sudden inflammation is caused by bacterial invasion. It occurs mainly in the interstitial tissue and the renal pelvis, and occasionally in the renal tubules. It may affect one or both kidneys. With treatment and continued follow-up care, the prognosis is good and extensive permanent damage is rare.

Pyelonephritis occurs more often in women than in men, probably because the shorter urethra and the proximity of the urinary meatus to the vagina and rectum allow bacteria to reach the bladder more easily. Women also lack the antibacterial prostatic secretions that men produce.

Typically, the infection spreads from the bladder to the ureters and then to the kidneys. commonly through vesicoureteral reflux. Vesicoureteral reflux may result from congenital weakness at the junction of the ureter and the bladder. Bacteria refluxed to intrarenal tissues may create colonies of infection within 24 to 48 hours.


Pyelonephritis most often occurs as a result of urinary tract infection , particularly in the presence of occasional or persistent backflow of urine from the bladder into the ureters or kidney pelvis.

Pyelonephritis can be further classified as follows: Acute uncomplicated pyelonephritis (sudden development of kidney inflammation), Chronic pyelonephritis, Reflux nephropathy.

Although cystitis (bladder infection) is common, pyelonephritis occurs much less often. The risk is increased if there is a history of cystitis, renal papillary necrosis, kidney stones, vesicoureteric reflux, or obstructive uropathy .

Signs and Symptoms

  • Flank pain or back pain
  • Severe abdominal pain (occurs occasionally)
  • Fever
    • Higher than 102 degrees Fahrenheit
    • Persists for more than 2 days
  • Chills with shaking
  • Warm skin
  • Flushed or reddened skin
  • Moist skin
  • Vomiting, nausea
  • Fatigue
  • General ill feeling
  • Painful urination
  • Increased urinary frequency or urgency
  • Need to urinate at night (nocturia)
  • Cloudy or abnormal urine color
  • Blood in the urine
  • Foul or strong urine odor

Diagnostic tests

Diagnosis requires a urinalysis and culture and sensitivity testing. Typical findings include:

  • pyuria. Urine sediment reveals leukocytes singly, in clumps, and in casts and, possibly, a few red blood cells.
  • significant bacteriuria. Urine culture reveals more man 100,000 organisms/µl of urine.
  • low specific gravity and osmolality. These findings result from a temporarily decreased ability to concentrate urine.
  • slightly alkaline urine pH.
  • proteinuria, glycosuria, and ketonuria. These conditions occur less frequently.

Blood tests and X-rays also help in the evaluation of acute pyelonephritis. A complete blood count shows an elevated white blood cell count (up to 40,000/µl) and an elevated neutrophil count. The erythrocyte sedimentation rate is also elevated.

Kidney-ureter-bladder radiography may reveal calculi, tumors, or cysts in the kidneys and the urinary tract. Excretory urography may show asymmetrical kidneys, possibly indicating a high frequency of infection.


Treatment centers on antibiotic therapy appropriate to the specific infecting organism after identification by urine culture and sensitivity studies. For example, Enterococcus requires treatment with ampicillin, penicillin G, or vancomycin. Staphylococcus requires penicillin G or, if the bacterium is resistant, a semisynthetic penicillin such as nafcillin, or a cephalosporin. Escherichia coli may be treated with sulfisoxazole, nalidixic acid, or nitrofurantoin; Proteus, with ampicillin, sulfisoxazole, nalidixic acid, or a cephalosporin; and Pseudomonas, with gentamicin, tobramycin, or carbenicillin.

When the infecting organism can't be identified, therapy usually consists of a broad-spectrum antibiotic, such as ampicillin or cephalexin. Antibiotics must be prescribed cautiously for elderly patients because of the combined effects of aging and pyelonephritis on renal function. Antibiotics also are used with caution in pregnant patients. In these patients, urinary analgesics such as phenazopyridine can help relieve pain.

Symptoms may disappear after several days of antibiotic therapy. Although urine usually becomes sterile within 48 to 72 hours, the course of such therapy ranges from 10 to 14 days. Follow-up treatment includes reculturing urine 1 week after drug therapy stops and then periodically for the next year to detect residual or recurring infection. A patient with an uncomplicated infection usually responds well to therapy and doesn't suffer reinfection.

If infection results from obstruction or vesicoureteral reflux, antibiotics may be less effective and surgery may be necessary to relieve the obstruction or correct the anomaly. A patient at high risk for recurring urinary tract and kidney infections - for example, a patient with a long-term indwelling catheter or on maintenance antibiotic therapy - requires lengthy follow-up care.

Few cases of pyelonephritis can be prevented by prompt recognition and treatment of minor bladder infections that, if left untreated, may progress to this more severe condition.

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