Upper UTI/Pyelonephritis
Pyelonephritis is a bacterial infection of the renal pelvis and renal parenchyma causing inflammation of the kidney. It represents the upper spectrum of urinary tract infection (UTI).
Acute Pyelonephritis
Acute suppurative bacterial infection involving:
- Renal pelvis/Collecting system/Renal interstitium/Renal tubules
Usually occurs due to:
- Ascending infection from lower urinary tract
- Less commonly hematogenous spread
Chronic Pyelonephritis
Chronic tubulointerstitial inflammation and scarring due to:
- Recurrent pyelonephritis/Vesicoureteral reflux/Chronic obstruction
Leads to:Renal scarring/Tubular atrophy/CKD/Hypertension
Risk Factors
|
Anatomical Factors |
Functional Factors |
Behavioral Factors |
|
Vesicoureteral reflux |
Pregnancy |
Frequent intercourse |
|
Urinary obstruction |
Diabetes mellitus |
Spermicide use |
|
Benign prostatic hyperplasia (BPH) |
Immunosuppression |
Poor hydration |
|
Ureteric stone |
Chronic kidney disease (CKD) |
|
|
Pelviureteric junction (PUJ) obstruction |
Catheterization |
|
|
Neurogenic bladder |
Urinary tract instrumentation |
|
|
Congenital urinary tract anomalies |
Urinary retention |
|
Etiology
|
Organism |
Comments |
|
Escherichia coli |
Most common (~70–90%) |
|
Klebsiella pneumoniae |
Common in healthcare-associated infection |
|
Proteus mirabilis |
Associated with struvite stones |
|
Enterococcus faecalis |
Elderly/catheterized |
|
Pseudomonas aeruginosa |
Instrumentation, ICU |
|
Staphylococcus saprophyticus |
Young women |
|
Candida albicans |
Catheterized/immunocompromised |
Routes of Infection
1. Ascending Infection (Most Common)
Pathogenesis:
- Colonization of periurethral area
- Ascending cystitis
- Vesicoureteral reflux
- Intrarenal reflux
- Renal infection
2. Hematogenous Spread
Less common.Seen with:
- Staphylococcus aureus bacteremia/Endocarditis
- IV drug abuse/Immunosuppression
Classification
|
Feature |
Acute Pyelonephritis (APN) |
Xanthogranulomatous Pyelonephritis (XGP) |
Emphysematous Pyelonephritis (EPN) |
|
Definition |
Acute bacterial infection of renal pelvis and parenchyma |
Rare chronic destructive granulomatous renal infection with replacement of renal tissue by lipid-laden macrophages |
Necrotizing renal infection characterized by gas formation within kidney and/or surrounding tissues |
|
Typical Organism |
E. coli (most common) |
Proteus mirabilis, E. coli |
E. coli (60–70%), Klebsiella, Proteus |
|
Pathogenesis |
Ascending UTI → renal infection |
Chronic obstruction + recurrent infection → granulomatous destruction |
Gas-producing organisms ferment glucose causing tissue necrosis and gas formation |
|
Underlying Mechanism |
Acute bacterial inflammation |
Lipid-laden macrophage infiltration (“xanthoma cells”) |
Necrosis + gas production in renal tissues |
|
Most Important Risk Factor |
Female sex |
Staghorn calculus |
Diabetes mellitus |
|
Radiology |
Striated nephrogram |
Bear Paw Sign |
Gas within renal parenchyma |
|
Treatment |
Antibiotics ± drainage if obstructed |
Nephrectomy after infection control |
ICU care + carbapenem-based antibiotics(2–3 weeks minimum) + DJ stent/PCN + percutaneous drainage; nephrectomy only if treatment fails |
Clinical Features
Classic Triad
- Fever
- Flank pain
- Nausea/vomiting
Symptoms
|
Symptom |
Mechanism |
|
Fever with chills |
Systemic inflammation |
|
Flank pain |
Renal capsule distension |
|
Dysuria |
Associated cystitis |
|
Frequency |
Lower UTI |
|
Urgency |
Bladder irritation |
|
Nausea/vomiting |
Cytokine response |
|
Malaise |
Systemic illness |
|
Hematuria |
Mucosal inflammation |
Physical Examination
|
Finding |
Significance |
|
Fever |
Infection |
|
Tachycardia |
Sepsis |
|
Hypotension |
Septic shock |
|
CVA tenderness |
Renal inflammation |
|
Suprapubic tenderness |
Cystitis |
|
Delirium |
Elderly sepsis |
Special Presentations
Elderly
May present with:
- Delirium
- Weakness
- Falls
- Sepsis without urinary symptoms
Pregnancy
Risk:
- Preterm labor
- ARDS
- Sepsis
Usually due to:
- Progesterone-mediated ureteric dilation
- Urinary stasis
Diabetics
Higher risk of:
- Emphysematous pyelonephritis
- Papillary necrosis
- Renal abscess
Diagnosis
Urinalysis
|
Finding |
Significance |
|
Pyuria |
Hallmark |
|
Leukocyte esterase |
WBCs |
|
Nitrite positive |
Gram-negative bacteria |
|
WBC casts |
Suggest upper UTI |
|
Mild proteinuria |
Tubular inflammation |
|
Hematuria |
Inflammation |
Urine Culture (Before Antibiotics)
Diagnostic Thresholds
|
Specimen |
Significant Growth |
|
Midstream urine |
≥10⁵ CFU/mL |
|
Symptomatic women |
≥10³ CFU/mL may be significant |
|
Catheter specimen |
≥10²–10³ CFU/mL |
Blood Tests
|
Investigation |
Findings |
|
CBC |
Leukocytosis |
|
CRP/ESR |
Elevated |
|
Procalcitonin |
May correlate with severity |
|
Renal function |
AKI |
|
Electrolytes |
Sepsis-associated changes |
|
Lactate |
Severe sepsis |
Blood Cultures
Positive in:15–30%
Indications:Sepsis/ICU/Immunocompromised/Severe pyelonephritis
Imaging(Diagnosis can often be made clinically without imaging.)
Ultrasound
Useful for:Hydronephrosis/Obstruction/Abscess/Stones
CECT Abdomen/Pelvis (Best Imaging)
Indications:
- Severe illness
- Persistent fever >48–72 h
- Suspected obstruction
- AKI
- Diabetes
- Immunocompromised
- Recurrent pyelonephritis
MRI
Alternative when:Pregnancy/Contrast contraindicated
Differential Diagnosis
|
Condition |
Distinguishing Features |
|
Renal colic |
Colicky pain, no fever |
|
Appendicitis |
RLQ pain |
|
Cholecystitis |
RUQ pain |
|
PID |
Pelvic findings |
|
Renal abscess |
Persistent fever |
|
Perinephric abscess |
Toxic appearance |
|
Glomerulonephritis |
RBC casts |
|
Lower UTI |
No flank pain/fever |
Complications
Local Complications
|
Complication |
Description |
|
Renal abscess |
Localized pus collection |
|
Perinephric abscess |
Extension outside kidney |
|
Papillary necrosis |
Seen in diabetes |
|
Emphysematous pyelonephritis |
Gas-forming infection |
|
Pyonephrosis |
Infected obstructed kidney |
Systemic Complications
|
Complication |
Description |
|
Sepsis |
Systemic inflammatory response |
|
Septic shock |
Vasopressor-requiring hypotension |
|
AKI |
Sepsis + tubular injury |
|
ARDS |
Severe inflammatory response |
|
DIC |
Severe sepsis |
Management
Uncomplicated Pyelonephritis (Outpatient)-Oral Options
|
Drug |
Typical Regimen |
|
Ciprofloxacin |
500 mg BD 7 days |
|
Levofloxacin |
750 mg OD 5 days |
|
TMP-SMX |
If susceptible known then-160/800 mg PO BD for 14 days |
|
Oral beta-lactams |
Less effective than fluoroquinolones. |
Oral Beta-Lactams
|
Drug |
Dose |
|
Amoxicillin-Clavulanate |
875/125 mg BD |
|
Cefpodoxime |
200 mg BD |
|
Cefixime |
400 mg OD |
Duration:10–14 days
If Local Fluoroquinolone Resistance >10%
Give a single IV long-acting agent first:
|
Initial Dose |
Then Oral Therapy |
|
Ceftriaxone 1 g IV once |
Ciprofloxacin/Levofloxacin |
|
Gentamicin 5–7 mg/kg IV once |
Oral regimen |
|
Amikacin 15 mg/kg IV once |
Oral regimen |
This is specifically recommended in IDSA guidance.
Hospitalized Patients(NO SEPTIC SHOCK)-IV Antibiotics
|
Antibiotic |
Uses |
|
Ceftriaxone 1–2 g IV OD |
Common empiric therapy,Community-acquired APN |
|
Piperacillin-tazobactam-4.5 g IV q6h |
Complicated infection,Hospital-acquired risk,Pseudomonas |
|
Cefepime-2 g IV q8h |
Hospital-acquired infection |
|
Carbapenem |
ESBL organisms |
|
Aminoglycosides |
Severe gram-negative infection |
ICU/Septic Shock
Empiric therapy should cover:
- ESBL organisms
- Pseudomonas aeruginosa if risk factors
- Resistant gram-negatives
Examples:
- Meropenem
- Piperacillin-tazobactam + amikacin
- Cefepime + aminoglycoside
Pregnancy
Preferred:
|
Drug |
Dose |
|
Ceftriaxone |
1–2 g IV OD |
|
Cefotaxime |
2 g IV q8h |
|
Amoxicillin-Clavulanate |
Step-down therapy |
Duration:10–14 days
Avoid:
- Fluoroquinolones
- Tetracyclines
Duration of Therapy
|
Situation |
Duration |
|
Uncomplicated |
5–7 days (fluoroquinolone) |
|
Complicated |
10–14 days |
|
Abscess |
2–4 weeks |
|
Bacteremia |
Usually 10–14 days |
Source Control
Urgent Urological Intervention Needed In:
- Obstructive pyelonephritis
- Pyonephrosis
- Infected stone
- Hydronephrosis with sepsis
Methods:
- Percutaneous nephrostomy
- Ureteric stenting
This is a urological emergency.
Suppurative Upper UTI
|
Feature |
Corticomedullary Abscess |
Renal Carbuncle(Renal Cortical Abscess) |
Pyonephrosis |
|
Definition |
Intrarenal abscess involving cortex and medulla |
Large cortical abscess produced by hematogenous infection with tissue necrosis |
Suppurative infection within an obstructed collecting system causing pus-filled hydronephrosis |
|
Alternative Name |
Intrarenal abscess |
Renal carbuncle |
Infected hydronephrosis |
|
Location |
Cortex + medulla |
Cortex |
Pelvicalyceal system |
|
Primary Pathogenesis |
Ascending UTI |
Hematogenous spread |
Obstruction + infection |
|
Typical Organism |
Gram-negative bacilli |
S. aureus |
E. coli, Klebsiella, Proteus, Pseudomonas |
|
Relation to UTI |
Usually present |
Usually absent |
Always present |
|
Surgical Emergency |
Sometimes |
Sometimes |
Always |
|
Main Treatment |
Antibiotics(2–6 weeks) + drainage
|
Antibiotics(4–6 weeks) ± drainage
IV antibiotics alone
Percutaneous drainage |
Urgent decompression |
Perinephric Abscess vs Paranephric Abscess
These are severe complications of upper urinary tract infection. The distinction is based primarily on anatomical location relative to Gerota’s fascia and the kidney.
Retroperitoneal Compartments
|
Space |
Boundaries |
Contents |
|
Perinephric (Perirenal) Space |
Between kidney capsule and Gerota’s fascia |
Kidney, adrenal gland, perirenal fat |
|
Paranephric (Pararenal) Space |
Outside Gerota’s fascia |
Fat and retroperitoneal tissues |
|
Feature |
Perinephric Abscess |
Paranephric Abscess |
|
Definition |
Collection of pus within perinephric space |
Collection of pus extending outside Gerota’s fascia into pararenal space |
|
Organ Involvement |
Kidney primarily |
Kidney + surrounding retroperitoneum |
|
Spread |
Limited by Gerota fascia |
No fascial containment |
Pathogenesis
Perinephric Abscess
Route 1 (Most Common)
Ascending UTI —>Acute Pyelonephritis—>Intrarenal Corticomedullary Abscess—>Rupture Through Renal Capsule—>Perinephric Abscess
Route 2
Hematogenous spread—>Renal cortical abscess—>Extension into perinephric fat —>Perinephric abscess
Paranephric Abscess
Pyelonephritis—>Renal Abscess—>Perinephric Abscess
—>Breakthrough Gerota Fascia—>Paranephric Abscess—>Retroperitoneal Spread—>Psoas/Abdominal Wall/Subphrenic Extension