Definition
Pyelonephritis is an infection of one or both kidneys usually caused by bacteria travelling up from the bladder.
Causes
The most common causative pathogens of acute pyelonephritis are gram-negative bacteria:
- Escherichia coli (60-80% of uncomplicated infections)
- Klebsiella species (20%)
- Proteus mirabilis (15%)
- Pseudomonas species
- Enterobacter species
Clinical Features
Acute pyelonephritis is diagnosed by taking a detailed medical history and a physical examination. Suspect acute pyelonephritis in people with signs or symptoms of a urinary tract infection accompanied by any signs or symptoms of pyelonephritis.
Signs and symptoms of UTI include:
- Dysuria
- Frequency
- Urgency
- Nocturia
- Suprapubic discomfort/tenderness
- Changes in urine appearance or consistency
Signs and symptoms of pyelonephritis include:
- Kidney pain/tenderness in back under ribs
- Flank pain, or costovertebral angle tenderness is present in 86% of people with pyelonephritis
- New/different myalgia, flu-like illness
- Shaking chills (rigors) or temperature 37.9°C or above (or below 36°C in people aged over 65 years)
- Fever is found in 77% of people with pyelonephritis
- Fever may be absent in people with early or mild cases, frail, older people, or in the immunocompromised
- Nausea/vomiting
Differential Diagnosis
The differential diagnosis of acute pyelonephritis is broad, and includes:
- Lower urinary tract infection
- Acute prostatitis
- Renal colic
- Pelvic inflammatory disease
- Acute abdominal conditions
- Gynaecological conditions
- Musculoskeletal disorders
- Lower lobe pneumonia
- Shingles
Investigations
In all people suspected of having acute pyelonephritis, arrange collection of a midstream urine (MSU) or catheter specimen of urine (CSU), to determine the infecting microorganism. Obtain a urine sample for culture before starting empirical drug treatment.
- Dipstick testing of urine for nitrites and leukocytes is not necessary, however it may be a useful adjunct to guide diagnosis in some clinical situations. It should not be used in people with an indwelling catheter or aged over 65 years.
- A definitive diagnosis of acute pyelonephritis is made in people with loin pain and/or fever if a UTI is confirmed by culturing a urinary pathogen from the urine, and other causes of loin pain and/or fever have been excluded.
Management
Antibiotic therapy
- When prescribing an antibiotic for acute pyelonephritis, take account of local antimicrobial resistance data and local protocols.
- Give oral antibiotics first line if the person can take oral medicines, and the severity of their condition does not require intravenous antibiotics.
- Review intravenous antibiotics by 48 hours and consider stepping down to oral antibiotics where possible.
First-choice oral antibiotics
Cefalexin, co-amoxiclav, trimethoprim or ciprofloxacin.
First-choice intravenous antibiotics
Co-amoxiclav, cefuroxime, ceftriaxone, ciprofloxacin, gentamicin or amikacin.
In pregnant women
First-choice oral antibiotic is cefalexin and first-choice intravenous antibiotic is cefuroxime.
Self-care advice
- Advise people with acute pyelonephritis about using paracetamol for pain, with the possible addition of a low-dose weak opioid such as codeine.
- Advise people with acute pyelonephritis about drinking enough fluids to avoid dehydration.
- Advise people to seek medical help if symptoms worsen at any time or symptoms do not start to improve within 48 hours of taking the antibiotic or the person becomes systemically very unwell.
Referral Pathway
Consider referring or seeking specialist advice for people with acute pyelonephritis if they:
- Are pregnant
- Are significantly dehydrated and unable take oral fluid or medicine
- Have a higher risk of developing complications — people with underlying disease (such as DM, immunocompromise or genitourinary tract abnormalities)
- Have recurrent episodes of UTI (for example, two or more episodes in a 6-month period)
For all children presenting with an unexplained fever of 38ºC or higher, or loin pain/tenderness suggesting pyelonephritis — send a urine sample for microscopy and culture within 24 hours, and consider referral to a paediatric specialist.
Admission Pathway
Admit people with acute pyelonephritis to hospital if it is severe or patient developed sign and symptoms of sepsis include:
- Significant tachycardia, hypotension, or breathlessness
- Marked signs of illness (such as impaired level of consciousness, perfuse sweating, rigors, pallor, significantly reduced mobility)
- A temperature greater than 38°C or less than 36°C
Complications
Complications of acute pyelonephritis include:
- Sepsis
- Parenchyma renal scarring
- Renal impairment or failure
- Recurrent urinary tract infections
- Renal abscess formation
- Preterm labour in pregnancy
- Emphysematous pyelonephritis