Acute pyelonephritis is a bacterial infection of the renal pelvis and kidney, most commonly caused by ascending Escherichia coli (>90% in young women), presenting with flank pain, fever, and urinalysis evidence of UTI. [1] Clinical presentations range from mild flank pain with low-grade fever to septic shock, with bacteremia rates varying from <10% to >50% depending on host factors. [1] The estimated annual incidence in the United States is 459,000–1,138,000 cases. [1]
1. History
- Onset and progression: Sudden onset of flank pain (unilateral or bilateral), fever, chills, malaise — ask about timing and rapidity of symptom development [1]
- Lower urinary tract symptoms: Dysuria, frequency, urgency, hematuria — present in ~80% but absent in up to 20% of patients [1-2]
- Systemic symptoms: Fever (may be absent early), rigors, nausea, vomiting, anorexia [3-4]
- Prior UTI history: Recent cystitis, prior pyelonephritis episodes, recurrent UTIs
- Recent antibiotic use or hospitalization: Increases risk of resistant organisms [1]
- Recent travel: Particularly to areas endemic for ESBL-producing organisms [1]
- Urologic history: Known stones, structural abnormalities, catheterization, recent urologic procedures [5]
- Pregnancy status: Must be assessed in all women of reproductive age [3]
- Important negatives: Vaginal discharge (suggests alternative diagnosis), diarrhea, cough, genital discharge [6]
2. Alarm Features
- Sepsis signs: Hypotension, tachycardia, tachypnea, altered mental status, lactate elevation [7]
- Inability to tolerate oral intake (persistent vomiting) [1]
- Urine pH ≥7.0 (suggests urease-producing organism, e.g., Proteus; associated with struvite stones) [1]
- New decrease in GFR to ≤40 mL/min (suggestive of obstruction) [1]
- Known or suspected urolithiasis with concurrent infection (obstructed infected system = urologic emergency) [1][8]
- Failure to improve within 48–72 hours of appropriate antibiotics [4][8]
- Abnormalities in multiple CBC cell lines (leukocytosis + thrombocytopenia + anemia) — highly correlated with ICU admission [3]
- Immunocompromised state, diabetes, pregnancy, advanced age — higher risk for complications [9]
3. Medications
- Empiric outpatient oral options:
- Fluoroquinolones (ciprofloxacin 500 mg BID or levofloxacin 750 mg daily × 5–7 days) — if local resistance <10% [1][10]
- TMP-SMX (160/800 mg BID × 7–14 days) — if susceptibility known or local resistance <10% [10]
- Oral 3rd-generation cephalosporins (cefpodoxime) — limited evidence but used in practice [11]
- Supplemental parenteral dose at discharge: Ceftriaxone 1 g IV, gentamicin, amikacin, or ertapenem — recommended when anticipated resistance to the oral agent exceeds 10% [1][11]
- Inpatient parenteral options: Ceftriaxone, fluoroquinolones IV, piperacillin-tazobactam, carbapenems (for ESBL concern), aminoglycosides [8][12]
- Contraindicated/avoid:
- Nitrofurantoin — does not achieve adequate renal tissue concentrations; only effective in the bladder [1]
- Oral fosfomycin — same limitation, urine-only concentrations [1]
- Fluoroquinolones carry FDA black box warnings (tendon rupture, neuropathy, aortic dissection) — weigh risk/benefit [11]
- IV-to-oral transition: The 2025 IDSA guideline suggests transitioning to oral therapy once clinically improving, able to take PO, and an effective oral option is available — even in the setting of gram-negative bacteremia [13]
- Duration: 7 days for fluoroquinolones; 10–14 days for TMP-SMX or beta-lactams [1][10]
4. Diet
- Aggressive hydration is essential — oral if tolerated, IV if not [1]
- No specific dietary triggers for pyelonephritis
- Encourage adequate fluid intake during recovery to maintain urine output
- Cranberry products have limited evidence for prevention of recurrent UTI and no role in acute treatment
5. Review of Systems
- GU: Dysuria, frequency, urgency, hematuria, flank pain, suprapubic pain
- GI: Nausea, vomiting, diarrhea, abdominal pain (may mimic intra-abdominal pathology)
- Constitutional: Fever, chills, rigors, malaise, fatigue
- Respiratory: Dyspnea (consider ARDS in severe cases, especially pregnancy) [3]
- Neurologic: Altered mental status (sepsis indicator) [7]
- OB/GYN: Vaginal discharge (alternative diagnosis), contractions (in pregnancy) [3]
6. Collateral History and Family History
- Collateral: Medication compliance, recent antibiotic courses, recent healthcare exposures, functional status in elderly patients
- Family history: Vesicoureteral reflux (familial predisposition), polycystic kidney disease, recurrent UTIs
- Social context: Ability to take oral medications at home, reliable follow-up, stable home situation — critical for disposition decisions [1]
7. Risk Factors
- Female sex (short urethra, proximity to GI flora) [1]
- Sexual intercourse (strongest behavioral risk factor in young women) [9]
- Recent spermicide use
- Prior UTI or pyelonephritis [9]
- Urinary tract obstruction (stones, BPH, strictures) [5]
- Indwelling urinary catheter or recent instrumentation [5]
- Diabetes mellitus [9]
- Immunosuppression (transplant, HIV, chemotherapy) [9]
- Pregnancy (physiologic hydronephrosis, ureteral dilation) [3]
- Advanced age (higher hospitalization rates) [1]
- Anatomic/congenital urinary tract abnormalities [9]
- Recent antibiotic use or hospitalization (risk for resistant organisms) [1]
8. Differential Diagnosis
- Nephrolithiasis/ureterolithiasis — colicky pain, hematuria, may coexist with infection (pyonephrosis = emergency) [1]
- Renal abscess/perinephric abscess — failure to improve on antibiotics, CT needed [1]
- Acute cholecystitis — right-sided pain, Murphy's sign, may overlap with right-sided pyelonephritis [1]
- Appendicitis — right lower quadrant/flank pain, especially retrocecal appendix [1]
- Pelvic inflammatory disease — lower abdominal pain, cervical motion tenderness, vaginal discharge [1]
- Acute prostatitis (in men) — fever + pyuria without flank pain [1]
- Renal vein thrombosis — flank pain, hematuria, proteinuria [1]
- Paraspinous muscle disorders — musculoskeletal flank pain without systemic signs [1]
- Emphysematous pyelonephritis — diabetic patients, gas on imaging, high mortality [9]
- Lower lobe pneumonia — may present with upper abdominal/flank pain and fever
9. Past Medical History
- Prior UTIs or pyelonephritis episodes (recurrence risk)
- Known urolithiasis or urologic surgery
- Diabetes mellitus (risk for emphysematous pyelonephritis, complicated course)
- Immunocompromising conditions
- Chronic kidney disease (baseline GFR important for comparison)
- Structural urinary tract abnormalities (vesicoureteral reflux, neurogenic bladder)
- Pregnancy history
- Drug allergies — particularly beta-lactams and fluoroquinolones
- Recent antibiotic use (resistance risk) [1]
10. Physical Exam
- Vital signs: Fever (≥38°C), tachycardia, hypotension (sepsis), tachypnea [2-3]
- CVA tenderness — the only physical exam finding that increases the probability of upper tract UTI; nearly pathognomonic when combined with fever and pyuria [2][4]
- Abdominal exam: Flank tenderness, suprapubic tenderness; assess for peritoneal signs (alternative diagnosis)
- Pelvic exam (if indicated): Rule out PID, vaginitis, cervicitis
- Skin: Assess for mottling, delayed capillary refill (sepsis)
- Mental status: Confusion or altered sensorium suggests sepsis [7]
- Absence of flank pain should raise suspicion for an alternative diagnosis [4]
11. Lab Studies
- Urinalysis with microscopy: Pyuria (WBC), bacteriuria, nitrites, leukocyte esterase — dipstick sensitivity ~75%, specificity ~82% for combined LE/nitrite [2]
- Urine culture with susceptibilities: Mandatory in all suspected pyelonephritis — the cardinal confirmatory test; typically ≥10⁴ CFU/mL of a uropathogen [1-2][8]
- Blood cultures: Not needed in uncomplicated cases; obtain if sepsis suspected, immunocompromised, or diagnostic uncertainty [8][14]
- CBC: Leukocytosis expected; multi-cell-line abnormalities predict adverse outcomes [3]
- BMP/CMP: Creatinine (assess for obstruction if GFR ≤40), electrolytes, glucose
- Lactate: If sepsis suspected [7]
- CRP/procalcitonin: Not routinely needed in uncomplicated cases; procalcitonin ≥0.50 ng/mL has ~82% sensitivity for bacteremia in febrile UTI [15]
- Pregnancy test: All women of reproductive age
12. Imaging
- Uncomplicated pyelonephritis: Imaging is NOT indicated [4][8]
- Indications for imaging: [1][9]
- Sepsis or septic shock
- Known or suspected urolithiasis
- Urine pH ≥7.0
- New GFR decrease to ≤40 mL/min
- Failure to improve within 48–72 hours
- Complicated patient (diabetes, immunocompromised, recurrent pyelonephritis)
- First-line: CT abdomen/pelvis with IV contrast — detection rate ~84% vs ~40% for ultrasound [9]
- CT findings: Focal/multifocal decreased parenchymal enhancement, renal swelling, perinephric stranding, abscess, gas (emphysematous pyelonephritis) [9]
- Ultrasound: Reasonable first-line in pregnancy and when CT is contraindicated; good for detecting hydronephrosis and stones but poor sensitivity for parenchymal changes [9]
- Non-contrast CT: Adequate if primary concern is urolithiasis [9]
13. Special Tests
- qSOFA score: ≥2 of altered mentation, SBP ≤100, RR ≥22 — identifies patients at risk for poor outcomes from sepsis [16]
- SOFA score: For ICU-level assessment of organ dysfunction [16]
- Point-of-care ultrasound (POCUS): Assess for hydronephrosis at bedside in the ED
- Bedside bladder scan: Evaluate for urinary retention
- Post-void residual: If obstruction suspected
14. ECG
- Not routinely indicated for uncomplicated pyelonephritis
- Obtain ECG if:
- Sepsis or hemodynamic instability (to evaluate for sepsis-related cardiac dysfunction)
- Elderly patients or those with cardiac comorbidities
- Pre-existing cardiac disease with new tachycardia
- ECG findings in sepsis-associated pyelonephritis: Sinus tachycardia (most common), QT prolongation (54% of sepsis patients), new atrial fibrillation/flutter (associated with poor outcomes, OR 2.19), ST-T wave changes [17]
- QT prolongation is particularly relevant given that fluoroquinolones (commonly used for pyelonephritis) also prolong QT — exercise caution with concurrent QT-prolonging medications [17]
15. Assessment
Typical presentation: Young woman with acute onset of fever, unilateral flank pain, CVA tenderness, dysuria/frequency, and pyuria/bacteriuria on UA. [1]
Atypical presentations to recognize
- Absence of lower urinary tract symptoms (~20%) [1]
- Absence of fever early in the course [4]
- Elderly patients may present with altered mental status, generalized weakness, or GI symptoms without classic localizing signs
- Bilateral pyelonephritis (less common, more severe)
Severity stratification: [1]
- Mild: Low-grade fever, minimal nausea, no vomiting, stable vitals → outpatient
- Moderate: Higher fever, vomiting, unable to tolerate PO initially → ED observation/short stay
- Severe: Sepsis, septic shock, hemodynamic instability, obstruction → admission
Complications: Renal/perinephric abscess, emphysematous pyelonephritis, urosepsis, septic shock, ARDS, renal insufficiency, preterm labor (in pregnancy) [1][3]
16. Treatment Plan
Initial stabilization
- IV fluid resuscitation if dehydrated or hemodynamically unstable [1]
- Antipyretics/analgesics (acetaminophen, NSAIDs if no renal contraindication)
- Antiemetics (ondansetron) if vomiting
Outpatient management (uncomplicated, tolerating PO, stable): [1][8]
- Fluoroquinolone (ciprofloxacin 500 mg PO BID × 7 days or levofloxacin 750 mg PO daily × 5 days) if local resistance <10%
- TMP-SMX DS PO BID × 14 days (or 7 days if susceptible E. coli) [10]
- Consider single dose of ceftriaxone 1 g IV or IM before discharge if resistance concern >10% [1][11]
Inpatient management (severe illness, unable to tolerate PO, sepsis, pregnancy, obstruction): [1][3][8]
- IV antibiotics: Ceftriaxone 1–2 g IV daily, fluoroquinolone IV, or piperacillin-tazobactam
- If ESBL concern: Carbapenem (ertapenem or meropenem) [12]
- Transition to oral therapy once clinically improving, afebrile, tolerating PO [13]
Source control: Urgent urologic decompression (percutaneous nephrostomy or ureteral stent) if obstructed infected system [1][8]
Pregnancy: Admit all patients; IV ampicillin + gentamicin or ceftriaxone; complete 14 days total therapy [3]
17. Disposition
Specialist consultation triggers
- Urology: Obstructing stone with infection, abscess requiring drainage, emphysematous pyelonephritis
- Infectious disease: MDR organisms, ESBL-producing pathogens, treatment failure, immunocompromised host [1]
18. Follow Up / Return Precautions
- Follow-up timing: Primary care or urology within 48–72 hours if discharged from ED; sooner if culture results require antibiotic change [8]
- Expected course: Most patients improve within 48–72 hours of appropriate antibiotics [4][8]
- Return immediately for:
- Worsening or persistent fever >48–72 hours on antibiotics
- Inability to keep down oral medications or fluids
- Worsening flank pain
- Signs of sepsis: confusion, lightheadedness, rapid heart rate, difficulty breathing
- Decreased urine output
- No routine follow-up testing needed if clinical course is uneventful [1]
- If no improvement at 48–72 hours: Repeat urine culture, obtain imaging (CT with contrast), and reconsider diagnosis [1][4][8]
- Patient counseling: Complete the full antibiotic course; maintain hydration; avoid nephrotoxic agents (NSAIDs with caution if renal function borderline)
References
1. Acute Pyelonephritis in Adults. — Johnson JR, Russo TA. The New England Journal of Medicine. 2018.
2. Uncomplicated Urinary Tract Infection. — Hooton TM. The New England Journal of Medicine. 2012.
3. Urinary Tract Infections in Pregnant Individuals. — Committee on Clinical Consensus—Obstetrics Obstetrics and Gynecology. 2023.
4. Diagnosis and Treatment of Acute Pyelonephritis in Women. — Colgan R, Williams M, Johnson JR. American Family Physician. 2011.
5. Clinical Practice Guideline by Infectious Diseases Society of America (IDSA): 2025 Guideline on Management and Treatment of Complicated Urinary Tract Infections: Introduction and Methods. — Barbara W. Trautner, Nicolás W. Cortés-Penfield, Kalpana Gupta, et al Infectious Diseases Society of America. 2025.
6. Ann Arbor Guide to Triaging Adults With Suspected Urinary Tract Infection for In-Person and Telehealth Settings. — Meddings J, Chrouser K, Fowler KE, et al. JAMA Network Open. 2026.
7. Sepsis and Septic Shock. — Meyer NJ, Prescott HC. The New England Journal of Medicine. 2024.
8. Acute Pyelonephritis in Adults: Rapid Evidence Review. — Herness J, Buttolph A, Hammer NC. American Family Physician. 2020.
9. ACR Appropriateness Criteria® Acute Pyelonephritis: 2022 Update. — Expert Panel on Urological Imaging, Smith AD, Nikolaidis P, et al. Journal of the American College of Radiology : JACR. 2022.
10. Appropriate Use of Short-Course Antibiotics in Common Infections: Best Practice Advice From the American College of Physicians. — Lee RA, Centor RM, Humphrey LL, et al. Annals of Internal Medicine. 2021.
11. Clinical Practice Guideline by Infectious Diseases Society of America (IDSA): 2025 Guideline on Management and Treatment of Complicated Urinary Tract Infections: Selection of Antibiotic Therapy for Complicated UTI. — Barbara W. Trautner, Nicolás W. Cortés-Penfield, Kalpana Gupta, et al Infectious Diseases Society of America. 2025.
12. Infectious Diseases Society of America 2024 Guidance on the Treatment of Antimicrobial-Resistant Gram-Negative Infections. — Tamma PD, Heil EL, Justo JA, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2024.
13. Clinical Practice Guideline by Infectious Diseases Society of America (IDSA): 2025 Guideline on Management and Treatment of Complicated Urinary Tract Infections: Timing of Intravenous to Oral Antibiotics Transition for Complicated UTI. — Barbara W. Trautner, Nicolás W. Cortés-Penfield, Kalpana Gupta, et al Infectious Diseases Society of America. 2025.
14. Early Care of Adults With Suspected Sepsis in The Emergency Department and Out-of-Hospital Environment: A Consensus-Based Task Force Report. — Yealy DM, Mohr NM, Shapiro NI, et al. Annals of Emergency Medicine. 2021.
15. A Reference Standard for Urinary Tract Infection Research: A Multidisciplinary Delphi Consensus Study. — Bilsen MP, Conroy SP, Schneeberger C, et al. The Lancet. Infectious Diseases. 2024.
16. Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021. — Evans L, Rhodes A, Alhazzani W, et al. Critical Care Medicine. 2021.
17. Association of Electrocardiogram Abnormalities With Clinical Outcomes in Emergency Department Sepsis Patients. — Kotruchin P, Chuehongthong M, Tangpaisarn T, et al. The Western Journal of Emergency Medicine. 2026.