Acute Pyelonephritis Clinical Presentation

Updated: May 31, 2023
  • Author: Tibor Fulop, MD, PhD, FACP, FASN; Chief Editor: Vecihi Batuman, MD, FASN  more...
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The classic presentation in acute pyelonephritis is the triad of fever, costovertebral angle pain, and nausea and/or vomiting. These may not all be present, however, or they may not occur together temporally. Symptoms may be minimal to severe and usually develop over hours or over the course of a day. Infrequently, symptoms develop over several days and may even be present for a few weeks before the patient seeks medical care. Symptoms of cystitis may or may not be present to varying degrees. These may include urinary frequency, hesitancy, lower abdominal pain, and urgency.

Gross hematuria (hemorrhagic cystitis) is present in 30-40% of pyelonephritis cases in females, most often young women. Gross hematuria is unusual in males and should prompt consideration of a more serious cause.

Pain may be mild, moderate, or severe. Flank pain may be unilateral or sometimes bilateral. Discomfort or pain may be present in the back (lower or middle) and/or the suprapubic area. Patients may describe suprapubic symptoms as discomfort, heaviness, pain, or pressure. Upper abdominal pain is unusual, and radiation of pain to the groin is suggestive of a ureteral stone.

Fever is not always present. When present, it is not unusual for the temperature to exceed 103°F (39.4°C). The patient may demonstrate rigor, and chills may be present in the absence of demonstrated fever. Malaise and weakness may also be present.

Gastrointestinal symptoms vary. Anorexia is common. Nausea and vomiting vary in frequency and intensity from absent to severe. Diarrhea occurs infrequently.

The classic signs and symptoms observed in adults are often absent in children, particularly neonates and infants. In children 2 years of age and younger, the most common symptoms of urinary tract infection (UTI) are failure to thrive, feeding difficulty, fever, and vomiting. When fever is present, pyelonephritis should be in the differential diagnosis.

Elderly patients may present with typical manifestations of pyelonephritis, or they may experience fever, mental status change, decompensation in another organ system, or generalized deterioration.

Complicated pyelonephritis

A history of the following indicates an increased risk of complicated pyelonephritis:

  • Structural abnormalities of the urinary tract
  • Functional abnormalities of the urinary tract
  • Metabolic abnormalities predisposing to UTIs
  • Recent antibiotic use
  • Recent urinary tract instrumentation

The presence of any one of the above complicating factors should raise the clinician’s index of suspicion. In many instances, more than one complicating factor is involved. In addition, if the patient is male, elderly, or a child or has had symptoms for more than 7 days, the infection should be considered complicated until proven otherwise.


Physical Examination

The patient may or may not have a fever. If fever is present, the temperature may be greater than 103°F (39.4°C). In contrast, the temperature may be subnormal in patients with associated sepsis. Tachycardia may or may not be present, depending on associated fever, dehydration, and sepsis.

Blood pressure is usually within the reference range, unless the patient has underlying hypertension, in which case the pressure may be elevated above the patient's baseline. A systolic blood pressure below 90 mm Hg suggests shock secondary to sepsis or perinephric abscess.

The patient's appearance is variable. Most commonly, the patient is uncomfortable or appears ill. Patients usually do not have a toxic appearance, unless there is an underlying problem, such as sepsis, perinephric abscess, or significant dehydration.

On abdominal examination, suprapubic tenderness usually ranges from mild to moderate without rebound. Abdominal tenderness other than in the suprapubic area suggests another diagnosis. Patients usually do not have rigidity or guarding, and bowel sounds are often normally active.

Flank or costovertebral angle (CVA) tenderness is most commonly unilateral over the involved kidney, although bilateral discomfort may be present. Discomfort varies from absent to severe. This finding is usually not subtle and may be elicited with mild or moderately firm palpation.

In women, a pelvic examination should be performed. Tenderness of the cervix, uterus, and adnexa should be absent. Any positive finding suggests an additional or alternative diagnosis. A gynecologic cause of the symptoms should be pursued if any of the following are present:

  • Doubt as to the diagnosis
  • Signs or symptoms of urethritis or vaginitis
  • A history of dyspareunia


Complications occur more often in patients with diabetes mellitus, chronic kidney disease, sickle cell disease, kidney transplant (particularly during the first 3 months), AIDS, and other immunocompromised states. It can sometimes be difficult to determine whether the entities listed below are occurring as a complication of pyelonephritis or are occurring in the absence of pyelonephritis but with signs and symptoms suggestive of pyelonephritis. The important point is to have a high index of suspicion for these complications.

Complications may involve any of the following:


Abscesses may include renal cortical abscess, renal corticomedullary abscess, or perinephric abscess. Older adults have a higher incidence of renal corticomedullary abscesses, which affect men and women equally.

Corticomedullary abscess

Patients with renal corticomedullary abscesses often present with chills, fever, and flank or abdominal pain, and patients may have dysuria and/or nausea and vomiting. Leukocytosis may be present. Bacteriuria, pyuria, hematuria, or proteinuria may be present, as the intrarenal abscesses drain in the collecting system, but the urinalysis results may be normal in as many as 30% of patients. Bacteremia may be observed in acute focal or multifocal bacterial nephritis.

Corticomedullary abscess is usually associated with a urinary tract abnormality, such as vesicoureteral reflux or obstruction. It is commonly caused by Enterobacteriaceae.

The pathology represents a spectrum of disease, as follows:

  • Acute focal bacterial nephritis (eg, acute lobar nephroma, focal pyelonephritis) that affects a single renal lobe, with interstitial inflammation represented by marked polymorphonuclear leukocytes
  • Acute multifocal bacterial nephritis, with a similar process throughout the kidney that produces liquefaction and abscess formation
  • Xanthogranulomatous pyelonephritis, with chronic parenchymal infection, granulomatous tissue, and perirenal fibrosis
  • Emphysematous pyelonephritis, with severe, necrotizing infection

Perinephric abscess

The suppurative material of the abscess is located between the renal capsule and the surrounding renal fascia. The material is secondary to chronic or recurrent pyelonephritis; rupture or extension of a suppurative process from within the kidney; or dissemination (blood, lymph) or direct extension from other sites of infection. Although it is usually confined to the perinephric space, it may extend to the colon, flank, groin, lung (empyema, nephrobronchial fistula), paracervical area, peritoneal cavity, psoas muscle, skin surface, or subphrenic space.

Development is insidious. Presentation may include the following:

  • Fever
  • Chills
  • Unilateral flank pain (70%)
  • Dysuria (40%)
  • Nausea
  • Vomiting
  • Weight loss (25%)
  • Flank tenderness
  • Costovertebral angle tenderness
  • Abdominal tenderness (60%)
  • Referred pain (ie, hip, thigh, or knee)
  • Flank or abdominal mass (< 50%)
  • Pyuria (70%)
  • Sterile urine (40%)
  • Bacteremia (40%)
  • Curvature of the spine away from the involved kidney

One third of patients are diagnosed upon admission; another third are diagnosed at autopsy. Perinephric abscess is not usually readily apparent; a high index of clinical awareness is necessary.

Renal cortical abscess

Renal cortical abscess (renal carbuncle) is an uncommon condition that is usually caused by the hematogenous spread of S aureus. It occurs 3 times more commonly in men than in women. Microabscesses develop in the cortex and coalesce to form a circumscribed abscess that may or may not communicate with the collecting system. This process takes days to months.

Patients with renal cortical abscess may present with chills, fever, and flank or abdominal pain. A flank mass or a bulge in the lumbar region may be evident. Some patients have abnormal results on lung examination of the affected side (dullness to percussion, rales). Blood and urine culture results usually are negative, but the white blood cell (WBC) count is often elevated.

Emphysematous pyelonephritis, pyelitis, and cystitis

Emphysematous pyelonephritis, which most commonly occurs in persons with diabetes, is a severe, necrotizing form of acute multifocal bacterial nephritis with extension of the infection through the renal capsule. This leads to the presence of gas within the kidney substance and in the perinephric space. Persons with diabetes (with or without obstruction) account for 85-100% of cases, although some cases have occurred in patients without diabetes who had obstruction. Females outnumber males (2-6:1).

Emphysematous pyelonephritis occurs in the left kidney in approximately two thirds of cases. The etiology is usually Enterobacteriaceae (E coli, 60%), with some reported cases of Streptococcus species and Candida species. A triad of diabetes, obstruction, and remote or recent pyelonephritis should raise clinical suspicion. Patient presentation includes fever, chills, abdominal pain, nausea, vomiting, flank pain, flank mass (50%), crepitation (over thigh or flank), urinary symptoms, and pyuria.

Emphysematous pyelitis (pneumopyonephrosis) involves gas that is localized to the collecting system. Diabetes mellitus is present in 85-100% of patients. The left kidney is more frequently affected than the right. Presentation is similar to that of pyelonephritis. On plain radiographs, the gas pattern is noted in the renal pelvis and may be seen in the ureter. The patient should be admitted and treated with intravenous antibiotics. The mortality rate is 20%.

Emphysematous cystitis (cystitis emphysematosa) involves gas that is localized to the bladder secondary to a bladder infection. Gas in the bladder is more frequently related to a fistula between the bladder and the colon or vagina than to a gas-producing infection. As many as 80% of patients are diabetic.

Patient presentation is similar to that for pyelonephritis. Plain radiographs may demonstrate gas in the bladder wall or lumen, an air-fluid level in the bladder, or a cobblestone appearance to the bladder wall. CT scan is the study of choice to help localize the gas to the proper organ. Treatment involves intravenous antibiotics and relief of any outlet obstruction. This condition is not as serious as the other two previously described emphysematous conditions.

Xanthogranulomatous pyelonephritis

Xanthogranulomatous pyelonephritis is a rare form of pyelonephritis that is almost always associated with chronic obstruction (eg, from staghorn calculus [75% of cases], other calculus, stricture, or tumor).  This disease is usually unilateral and most frequently affects the right kidney. [13]

In adults, the female-to-male ratio is 3:1; in children, it is 1.1:1. It is a chronic infection that finally manifests acutely with fever and flank pain or tenderness, and it may be complicated by a flank mass, cutaneous fistula, septic arthritis, or hematochezia if extension has occurred beyond the renal capsule. Kidney function is absent (71%) or poor (25%) in almost all cases.  A biopsy should be performed to confirm the diagnosis and exclude renal carcinoma. [13]


Tuberculosis (TB) of the kidney results from hematogenous spread but is relatively rare in developing countries. Unlike most other extrapulmonary manifestations of the disease, TB of the kidney does not become manifest until 5-15 years after the primary infection. Constitutional symptoms are uncommon, and most patients present with symptoms of bladder irritation.

Initially, pyuria is observed, and with progression of the disease, proteinuria and blood may be observed as well. Repeated urine samples should be sent for mycobacterial culture. A loss of calyceal architecture and ureteric obstruction may be observed on imaging studies.

Concurrent pulmonary disease is present in 5% of patients, and the tuberculin test rarely is helpful. Antituberculous medicines should be administered for 6 months. If the ureter is obstructed, corticosteroids have been advocated; if obstruction persists, surgical intervention is necessary.