Pyelonephritis
Acute bacterial infection of the renal parenchyma and collecting system, usually caused by ascending infection from the lower urinary tract. E. coli is responsible for 70-80% of cases. Presents with fever, loin pain, and systemic upset. Can lead to sepsis, renal abscess, or chronic scarring.
Key Facts
Acute pyelonephritis is a serious upper UTI caused by E. coli (70-80%) with fever, loin pain, and costovertebral angle tenderness More common in women, pregnancy, diabetes, urinary obstruction, and vesicoureteric reflux NICE NG111: mild cases (oral): cefalexin 500mg TDS or co-amoxiclav 500/125mg TDS for 7-10 days Severe/septic: IV antibiotics (co-amoxiclav, piperacillin-tazobactam, or gentamicin per local protocol) MSU and blood cultures should be sent before starting antibiotics Complications: renal abscess, perinephric abscess, emphysematous pyelonephritis (diabetics – surgical emergency), sepsis CT abdomen: indicated if no improvement after 48-72 hours of IV antibiotics (exclude abscess/obstruction)
Overview
Key Facts
Pyelonephritis requires prompt antibiotic therapy and assessment for complications. It can rapidly progress to urosepsis, particularly in patients with obstruction or immunosuppression.
Epidemiology
- Incidence: 15-17 per 10,000 women/year; 3-4 per 10,000 men/year
- Peak age: reproductive years (women), elderly (both sexes)
- Pregnancy: 1-2% of pregnancies; 20-40% of untreated asymptomatic bacteriuria progresses to pyelonephritis
Aetiology
- Ascending infection from lower urinary tract (most common route)
- Haematogenous spread (rare): Staphylococcus aureus from distant focus
- Organisms: E. coli (70-80%), Klebsiella, Proteus, Enterococcus, Pseudomonas
Pathophysiology
- Bacteria ascend from bladder via ureters to renal pelvis and parenchyma
- Vesicoureteric reflux facilitates ascent
- Infection causes acute inflammation with neutrophil infiltration, tubular damage, and interstitial oedema
- Can lead to abscess formation, papillary necrosis (particularly in diabetics), and renal scarring
Clinical Presentation
Typical Presentation
- Fever (>38°C), rigors, chills
- Loin/flank pain (unilateral, dull aching)
- Costovertebral angle tenderness on examination
- Nausea and vomiting
- Lower urinary tract symptoms may or may not be present (dysuria, frequency)
Severe/Complicated
- Sepsis: tachycardia, hypotension, confusion
- Renal abscess: swinging fever, failure to respond to antibiotics
- Emphysematous pyelonephritis: gas within renal parenchyma (diabetics); surgical emergency
Red Flags
- Sepsis (NEWS2 ≥5) → IV antibiotics, fluid resuscitation, senior review
- No improvement after 48-72 hours → imaging for abscess/obstruction
- Pregnant with pyelonephritis → hospital admission, IV antibiotics
- Known urinary obstruction + infection → emergency nephrostomy/drainage (pyonephrosis)
Differential Diagnosis
| Diagnosis | Key Features | Investigation |
|---|---|---|
| Renal colic | Colicky loin-to-groin pain, haematuria, afebrile | CT KUB |
| Appendicitis | RIF pain, migration from umbilicus | CT abdomen, clinical |
| Cholecystitis | RUQ pain, Murphy's positive | USS abdomen |
| Lower lobe pneumonia | Cough, pleuritic chest pain, referred abdominal pain | CXR |
| Renal infarction | Sudden loin pain, LDH elevated, AF | CT angiography |
| Perinephric abscess | Prolonged fever, flank mass | CT abdomen |
Diagnosis / Investigation
Bedside
- Urine dipstick: nitrites, leucocytes, blood
- Observations: temperature, NEWS2 score
Bloods
- FBC: raised WCC (neutrophilia)
- CRP: elevated
- U&Es: renal function (AKI risk)
- Blood cultures: before antibiotics (positive in 20-30%)
- Lactate: if sepsis suspected
Microbiology
- MSU: for culture and sensitivity before antibiotics
Imaging
- Not routine for uncomplicated pyelonephritis
- Renal USS or CT: indicated if:
- No clinical improvement after 48-72 hours IV antibiotics
- Suspected obstruction (pyonephrosis)
- Recurrent pyelonephritis
- Atypical presentation
- CT abdomen with contrast: best for abscess, emphysematous pyelonephritis
- DMSA scan: assess renal scarring (particularly in children with VUR)
Management
Mild Pyelonephritis (Outpatient)
- Cefalexin 500mg TDS or co-amoxiclav 500/125mg TDS for 7-10 days (NICE NG111)
- Trimethoprim 200mg BD for 14 days if culture-sensitive
- Adequate oral fluids, regular paracetamol
- Safety-netting: return if worsening, vomiting, unable to take oral medications
Severe Pyelonephritis (Inpatient)
- IV co-amoxiclav 1.2g TDS or IV piperacillin-tazobactam 4.5g TDS (per local antibiotic guidelines)
- IV gentamicin 5-7mg/kg (single dose, OD dosing): for sepsis or resistant organisms
- IV-to-oral switch when: afebrile for 24-48 hours, improving clinically, tolerating oral intake
- Total course: 7-14 days
Complicated Pyelonephritis
- Obstruction with infection (pyonephrosis): emergency nephrostomy or ureteric stent + IV antibiotics
- Renal abscess (>3cm): percutaneous drainage + prolonged antibiotics (4-6 weeks)
- Emphysematous pyelonephritis: IV antibiotics ± nephrectomy (high mortality 20-40%)
In Pregnancy
- Hospital admission for IV antibiotics
- IV cefuroxime 1.5g TDS or IV amoxicillin + gentamicin (per local protocol)
- Monitor for preterm labour
- Follow-up urine cultures to confirm clearance
Referral Criteria
- Recurrent pyelonephritis → urology (structural assessment)
- Failure to respond to treatment → imaging for abscess/obstruction
- Sepsis → acute medicine/ICU
Prognosis
- Uncomplicated pyelonephritis: full recovery in >95% with appropriate treatment
- Bacteraemia: occurs in 20-30%; increases ICU admission risk
- Renal scarring: risk increases with recurrent infections, VUR, and delayed treatment
- Emphysematous pyelonephritis: mortality 20-40% even with treatment
- Pyelonephritis in pregnancy: risk of preterm delivery; 20-40% bacteraemia rate if untreated
- Chronic pyelonephritis: repeated infections can lead to CKD and hypertension
Other Relevant Information
Emphysematous Pyelonephritis Classification
| Class | Description | Management |
|---|---|---|
| 1 | Gas in collecting system only | IV antibiotics + drainage |
| 2 | Gas in renal parenchyma | IV antibiotics + drainage |
| 3A | Extension to perinephric space | Drainage ± nephrectomy |
| 3B | Extension beyond Gerota's fascia | Nephrectomy likely |
| 4 | Bilateral or solitary kidney | Emergency management |
Risk Factors for Complicated Pyelonephritis
| Factor | Risk |
|---|---|
| Diabetes mellitus | Emphysematous, papillary necrosis |
| Urinary obstruction | Pyonephrosis |
| Immunosuppression | Abscess formation |
| Pregnancy | Urosepsis, preterm labour |
| Structural abnormality | Recurrence, scarring |