Recommendations
Urgent
Suspect acute pyelonephritis in a patient presenting with flank pain, myalgia or flu-like symptoms, fever, nausea, or vomiting, commonly in the context of the key signs and symptoms of a lower urinary tract infection (e.g., frequency, urgency, and dysuria).[27]
Think ‘Could this be sepsis?’ based on acute deterioration in a patient in whom there is clinical evidence or strong suspicion of infection.[27][28][29][30] See our topic Sepsis in adults.
Use a systematic approach (e.g., National Early Warning Score 2 [NEWS2]), alongside your clinical judgement, to assess the risk of deterioration due to sepsis. Consult local guidelines for the recommended approach at your institution.[28][29][30][31]
In the community: refer for emergency medical care in hospital (usually by blue-light ambulance in the UK) any patient who is acutely ill with a suspected infection and is:[28]
Deemed to be at high risk of deterioration due to organ dysfunction (as measured by risk stratification)
At risk of neutropenic sepsis.
In hospital: urgently consult a senior clinical decision-maker (e.g., ST4 level doctor in the UK) if you suspect sepsis.[28][29][30][32]
Send urine for culture before giving antibiotics if there are signs or symptoms of sepsis in a patient with suspected urinary tract infection.[27]
The patient may present with non-specific or non-localised symptoms (e.g., acutely unwell with a normal temperature) or there may be severe signs with evidence of multi-organ dysfunction and shock.[28][30][31]
Perform urinalysis and send urine for culture (before giving antibiotics) to confirm the diagnosis and identify the infective organism.
Use imaging to exclude other urgent urological disorders (e.g., obstruction requiring catheterisation) or complicated pyelonephritis (e.g., abscess formation), which may lead to sepsis.[34]
Consider onward referral and further investigation for suspected urological cancer, such as prostate, renal, or bladder cancer. Refer the patient using a suspected cancer pathway referral.[35]
Key Recommendations
Consider predisposing factors, such as a history of urinary tract infection, stress incontinence, diabetes, catheter in situ, renal stones, anatomical or functional urinary abnormality, or immunosuppression.
In men, urinary symptoms along with fever or systemic symptoms may also indicate acute prostatitis.[27]
Determine whether the patient is pregnant.
Check for the following signs and symptoms of acute pyelonephritis, commonly in the context of key lower urinary tract infection symptoms of urinary frequency, urgency, and dysuria:
New or different myalgia, or flu-like symptoms
Symptoms typically develop rapidly, within hours or over the course of a day.
Acute uncomplicated pyelonephritis most often develops as a result of an ascending urinary tract infection.[36] Symptoms of lower urinary tract infection (dysuria, frequency, urgency, nocturia) may or may not be present.[34]
Consider acute pyelonephritis to be ‘complicated’ if the patient has a structural or functional urinary tract abnormality, an underlying disease that increases the risk of a more serious outcome or has treatment failure, or sepsis.
Examples of complicated pyelonephritis include an obstruction requiring catheterisation, acute kidney injury, abscess formation, or antibiotic failure.
Consider all urinary tract infections in men, including acute pyelonephritis, to be complicated.[34]
Frail, older, or immunocompromised patients may not display the classic symptoms of pyelonephritis.[33] Fever may be absent.[33] Deterioration may be more rapid.
In men, urinary symptoms along with fever or systemic symptoms may also indicate acute prostatitis.[27] See the Differentials section.
Practical tip
Think ‘Could this be sepsis?’ based on acute deterioration in a patient in whom there is clinical evidence or strong suspicion of infection.[27][28][29][30] See our topic Sepsis in adults.
Use a systematic approach (e.g., National Early Warning Score 2 [NEWS2]), alongside your clinical judgement, to assess the risk of deterioration due to sepsis. Consult local guidelines for the recommended approach at your institution.[28][29][30][31]
In the community: refer for emergency medical care in hospital (usually by blue-light ambulance in the UK) any patient who is acutely ill with a suspected infection and is:[28]
Deemed to be at high risk of deterioration due to organ dysfunction (as measured by risk stratification)
At risk of neutropenic sepsis.
In hospital: urgently consult a senior clinical decision-maker (e.g., ST4 level doctor in the UK) if you suspect sepsis.[28][29][30][32]
Send urine for culture before giving antibiotics if there are signs or symptoms of sepsis in a patient with suspected urinary tract infection.[27]
The patient may present with non-specific or non-localised symptoms (e.g., acutely unwell with a normal temperature) or there may be severe signs with evidence of multi-organ dysfunction and shock.[28][30][31]
Remember that sepsis represents the severe, life-threatening end of infection.[37]
Urosepsis can result from ascending infection.
The urinary tract is the fourth most common site of infection in people with sepsis.[38] The genitourinary tract is the the most common site of infection in people aged over 65 years with sepsis.[39]
Consider onward referral and further investigation for suspected urological cancer, such as prostate, renal, or bladder cancer.[35] See the Best Practice topics on these conditions for more information.
Take a detailed medical history.
Ask whether any of the following symptoms are present:
New or different myalgia, or flu-like symptoms
Ask about the following risk factors:
Stress incontinence[8]
Diabetes[8]
Presence of a catheter or renal stones
Anatomical or functional urinary abnormality
Consider polycystic disease, enlarged prostate, vesicoureteric reflux, ureteroceles, and neurogenic bladder
Immunosuppression
Consider use of corticosteroids
Family history of UTI[8]
Frequent sexual intercourse, new sexual partner in the previous year, recent spermicide use.[8]
Practical tip
Older age, menopause, and structural abnormalities or obstructions of the urinary tract in women are risk factors for UTI, but not necessarily for acute pyelonephritis.
Determine whether the patient is pregnant. Carry out a pregnancy test if the patient is unsure.
UTIs are common during pregnancy. Infections and untreated asymptomatic bacteriuria during pregnancy are associated with an increased risk of pyelonephritis, premature delivery, and fetal mortality.[40]
Ask about previous antibiotic use when taking the history as it will be a consideration when planning the treatment regimen.[33]
Check vital signs, including:[27][33]
Temperature
A temperature >37.9°C (or ≤36°C in women aged over 65 years) can indicate pyelonephritis[27]
Tachycardia
May indicate an unwell or haemodynamically unstable patient
Hypotension
May indicate an unwell or haemodynamically unstable patient.
Look for any further signs of systemic illness or sepsis, such as tachypnoea, acutely altered mental status, mottled skin, or ashen appearance.
Evaluate the patient’s volume status. A young person can maintain a normal blood pressure but can be markedly hypovolaemic.
Palpate the costovertebral angle.
Tenderness is a key finding on examination and can help differentiate the presentation from flank pain due to renal or ureteral stones.[33][34]
Palpate the abdomen for suprapubic tenderness.[33]
Abdominal tenderness is common in patients with acute pyelonephritis.
In a patient with a kidney transplant, the kidney is generally easily palpable in the left or right lower quadrant of the abdomen depending on where it has been implanted.
Consider a digital rectal examination to rule out prostatitis and prostate cancer in men. See the Differentials section.
Urinalysis
Obtain a midstream, clean-catch urine sample. Perform a dipstick for urinalysis routinely in all patients with suspected acute pyelonephritis to confirm the diagnosis.[34] Assess for white blood cells, red blood cells, and nitrites.[34]
Note that Public Health England guidance differs from European guidelines; it advises not to perform urine dipsticks in patients over 65 years of age as the results become more unreliable with age.[27]
Practical tip
A urine dipstick test looks for positive leukocytes or nitrites to indicate a urinary tract infection (UTI).[3] Organisms such as Escherichia colior Klebsiella, Enterobacter, Proteus, Staphylococcus, or Pseudomonas species reduce nitrate to nitrite in the urine; therefore, the presence of nitrite on a urinalysis is an indicator of a UTI.[41]
Results indicating pyelonephritis include:[27][33]
Positive for leukocytes
Positive for nitrites
Non-visible haematuria
Visible haematuria is rare in acute pyelonephritis and more common in acute uncomplicated cystitis[33]
White blood cell casts
Indicate pyuria of renal origin.
Urine culture, microscopy, and sensitivity
Obtain a midstream, clean-catch urine sample to send for culture, microscopy, and susceptibility testing before antibiotics are taken.[33][34][36]
Antimicrobial susceptibility testing will help to inform definitive treatment.[27][34]
Over 95% of women with uncomplicated acute pyelonephritis will have >100,000 colony-forming units (CFU)/mL of a single gram-negative organism.[33]
Advise the patient on how to collect the sample:[27]
Women catching midstream urine samples can try to part the labia if possible to help reduce contamination.[27] Men should pull back the foreskin
Recommend against cleaning the area with antiseptic as this can inhibit bacteria[27]
Catch a sample in a sterile container in an older patient with incontinence[27]
In a patient with a catheter, collect from the sampling port using an aseptic technique.[27]
Consider sending a repeat sample if mixed growth or epithelial cells are present in a patient with symptoms of a lower UTI.[27] Consider a repeat sample after 2 to 3 days of therapy if symptoms do not improve, or if symptoms recur within 2 weeks of treatment.[33]
Consider the presenting signs and symptoms when interpreting the result.[27]
Blood tests
Send blood samples for routine analysis, including:
Full blood count
Check for leukocytosis, which is present in acute infection
Erythrocyte sedimentation rate
C-reactive protein
Urea and electrolytes
Creatinine.
Blood culture
Request a blood culture in a patient requiring admission to hospital.[33] Do not request routinely in a patient with uncomplicated pyelonephritis.
Draw blood before administering antibiotics.
Check for the presence of bacterial growth.
Between 15% and 30% of people with acute pyelonephritis are found to be bacteraemic on blood culture.[33]
Do not order imaging routinely for diagnosing acute uncomplicated pyelonephritis.[33][34] Use imaging if you suspect complications or if there is diagnostic uncertainty.
Use ultrasound to rule out urinary tract obstruction or renal stone disease in a patient with a history of urolithiasis, renal function disturbances, or a high urine pH.[34]
Request computed tomography (CT) in a patient if renal stones are not seen on ultrasound but they are still suspected clinically.
Consider contrast-enhanced CT if a patient remains febrile after 72 hours of treatment, or immediately if their clinical status deteriorates.[34]
Consider the risks of contrast-induced acute kidney injury in a patient with reduced kidney function.[33]
In pregnant women, use ultrasound or request magnetic resonance imaging preferentially to avoid radiation risk to the fetus when diagnosing complications.[34]
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