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Health condition · Clinically reviewed

Kidney infection, antibiotics, imaging - and knowing when a kidney needs draining.

Not just a bad water infection - pyelonephritis is a systemic illness that can tip into sepsis. Fast recognition, the right antibiotic and prompt drainage when the kidney is blocked change outcomes.

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Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against NICE, EAU and BSAC antimicrobial standards you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK practice, including sepsis pathways, IV antibiotics and drainage of an obstructed infected kidney.

Key facts

Kidney infection at a glance.

The essentials, in plain English - what pyelonephritis is, the different patterns of disease and how the NHS and private urology teams treat it today.

  • What it is

    Upper urinary tract infection - inflammation of the kidney and renal pelvis, usually bacterial and driven most often by Escherichia coli.

  • Main types

    Acute, complicated, chronic, emphysematous pyelonephritis and pyonephrosis - each with its own urgency and treatment plan.

  • Classic picture

    Fever with rigors, loin or flank pain, dysuria, urinary frequency and, at times, blood in the urine and vomiting.

  • Sepsis risk

    A kidney infection can tip into urosepsis quickly - the Sepsis Six pathway saves lives when applied early.

  • First-line care

    Prompt antibiotics guided by NICE and BSAC, fluid resuscitation, analgesia and imaging when the picture is complicated.

  • When to drain

    An obstructed, infected kidney needs urgent decompression with a nephrostomy or JJ ureteric stent - not antibiotics alone.

Why this guide matters

An urgent illness that rewards clear thinking.

Kidney infection is common, treatable and, when caught early, usually resolves fully. The three ideas below thread through everything else on this page.

  • It is a systemic illness

    This is not a simple bladder infection - fever, rigors and loin pain reflect infection reaching the kidney tissue itself.

  • Sepsis pathways save lives

    Applying the Sepsis Six within an hour of recognition is the single biggest lever on outcomes in urosepsis.

  • Obstruction changes the plan

    An obstructed infected kidney needs urgent drainage with a nephrostomy or ureteric stent - antibiotics alone are not enough.

How the diagnosis is made

From first fever to a clear plan.

The steps a UK GP, emergency doctor or urologist will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    History and red flags

    A structured history covering fever, loin pain, urinary symptoms, pregnancy status, stones, catheters and immune suppression.

  2. 02

    Assessing

    Bedside urinalysis and culture

    Dipstick, mid-stream urine and culture confirm infection and identify the organism and its sensitivities.

  3. 03

    Assessing

    Bloods and inflammatory markers

    FBC, U&Es, CRP and lactate assess severity, kidney function and the risk of sepsis.

  4. 04

    Confirming

    Blood cultures if unwell

    Taken before antibiotics in anyone with rigors, high fever or suspected sepsis - crucial for tailoring later therapy.

  5. 05

    Confirming

    Renal ultrasound

    A renal ultrasound scan (see /treatments/renal-ultrasound-scan/) looks for obstruction, stones, abscess or failure to respond.

  6. 06

    Confirming

    CT KUB when needed

    Non-contrast or contrast CT KUB - see /tests/private-ct-scan/ - is used for stones, abscess or complications.

  7. 07

    Preparing

    Specialist urology and microbiology

    Complicated, recurrent or drainage-requiring cases move into consultant-led urology and microbiology care.

Typical timeline: from first presentation to targeted therapy within hours, not days.

Symptoms

What a kidney infection feels like.

The classic mix of fever, loin pain and urinary symptoms - and the features that lift this from a bladder problem into a systemic illness needing urgent care.

  • Fever and rigors

    A high temperature and shaking chills are the hallmark systemic feature of an upper urinary tract infection.

  • Loin or flank pain

    A deep, one-sided ache over the kidney - often tender to gentle percussion on examination.

  • Dysuria, frequency and urgency

    Lower urinary tract symptoms often ride alongside kidney infection - burning, urgency and going more often than usual.

  • Nausea and vomiting

    A very common feature - it can also make oral antibiotics unreliable and shift the plan to intravenous treatment.

  • Visible or invisible haematuria

    Blood in the urine can be seen or picked up on dipstick and warrants a repeat check once the infection has settled.

  • Confusion in older adults

    New confusion, drowsiness or a fall can be the only clue in older or frail patients - a low threshold for assessment is essential.

  • Pregnancy presentations

    Pyelonephritis in pregnancy needs urgent hospital review - it can complicate the pregnancy and the baby quickly.

  • Red flag - sepsis features

    Low blood pressure, fast heart rate, mottled skin or reduced urine output are urosepsis until proven otherwise.

Treatment

How kidney infection is treated in the UK.

Prompt antibiotics, fluids and analgesia for most - drainage, sepsis bundles and specialist urology for the sickest and most complex.

  • Empirical IV antibiotics

    Co-amoxiclav, ceftriaxone or piperacillin-tazobactam per local BSAC and antimicrobial policy, then narrowed once cultures return.

  • Oral antibiotic step-down

    Ciprofloxacin or trimethoprim are used selectively for milder or improving disease, guided by sensitivities and NICE.

  • Fluid resuscitation

    Intravenous fluids restore circulating volume, support the kidneys and reduce the risk of tipping into shock.

  • Analgesia and antiemetics

    Simple analgesia, opioids where needed and antiemetics let patients tolerate oral intake and antibiotics.

  • Urgent drainage

    An obstructed, infected system needs a nephrostomy or a JJ ureteric stent (see /treatments/jj-ureteric-stent/) without delay.

  • Sepsis Six bundle

    Oxygen, cultures, IV antibiotics within one hour, fluids, lactate and urine output measurement - the backbone of urosepsis care.

  • Abscess drainage

    A renal or perinephric abscess may need image-guided percutaneous drainage alongside targeted antibiotics.

  • Long-term prevention plan

    For recurrent infection, low-dose prophylaxis, self-start regimens or a full urological workup for reflux, stones and obstruction.

What this guide is based on

The sources behind every claim on this page.

UK national guidance, European urology standards and antimicrobial policy, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP or urologist knows your history and can tell you which parts apply to you. If in doubt, and especially if you feel very unwell, get seen urgently.

  • NICE. Pyelonephritis (acute): antimicrobial prescribing (NG111).

  • European Association of Urology (EAU). Guidelines on urological infections.

  • BSAC. Standards for antimicrobial prescribing and urosepsis.

  • UK Sepsis Trust. Sepsis Six and screening tools for adult inpatients.

Red flags

When a kidney infection needs urgent attention.

Most cases settle with prompt antibiotics. These are the situations that do not - and where specialist urology, drainage or intensive care may be needed.

  • Urosepsis

    Fever with low blood pressure, fast heart rate, confusion or reduced urine output - an emergency triggering the Sepsis Six pathway.

  • Obstructed infected kidney

    A blocked kidney with infection behind it is a surgical emergency - antibiotics alone will not clear it without drainage.

  • Pyonephrosis

    Pus in an obstructed collecting system - needs urgent decompression with a nephrostomy or ureteric stent.

  • Emphysematous pyelonephritis

    A rare, gas-forming infection, seen most often in poorly controlled diabetes - specialist commissioned emergency care is required.

  • Pregnancy

    Any suspected kidney infection in pregnancy warrants urgent hospital review to protect both mother and baby.

  • Persistent fever after 72 hours

    Failure to improve on appropriate antibiotics prompts urgent imaging to look for obstruction, stones or an abscess.

  • Recurrent or bilateral disease

    Repeated attacks or infection in both kidneys point to an underlying urological or structural cause needing specialist review.

  • Immunocompromised or transplant patient

    Lower thresholds for admission and imaging - infection can progress rapidly and quietly in these groups.

  • Catheterised patients

    Long-term catheters change both the flora and the presentation - specialist input and catheter review are needed.

Living with it

A treatable illness, with a clear pathway.

Four things that make the biggest difference through and after treatment - patience with recovery, steady hydration, finishing every antibiotic course and dealing with anything upstream that keeps causing trouble.

A quiet reminder

Recurrence is a signal, not a sentence.

Two or more kidney infections in a year is a reason to look deeper - stones, reflux, obstruction and hydronephrosis often lie behind repeat attacks.

  1. 01 Recovery

    Give it time

    Even with prompt treatment, tiredness and mild loin ache can linger for a couple of weeks - rest is part of the plan.

  2. 02 Fluids

    Keep drinking

    A steady intake of water helps the kidneys clear infection and reduces the risk of recurrence.

  3. 03 Follow-up

    Complete every course

    Finishing the antibiotic course fully - and returning for review - lowers relapse and resistance.

  4. 04 Prevent

    Address the cause

    Stones, reflux, an enlarged prostate or a poorly draining kidney need attention - see /conditions/hydronephrosis/.

Frequently asked

Everything we get asked about kidney infection.

Quick answers on antibiotics, imaging, drainage and preventing recurrence.

  • What is a kidney infection?

    A kidney infection, or pyelonephritis, is an upper urinary tract infection - inflammation of the kidney and its renal pelvis, usually caused by bacteria such as Escherichia coli travelling up from the bladder.

  • How is it different from a bladder infection?

    A bladder infection tends to cause burning, urgency and frequency without systemic upset. A kidney infection adds fever, rigors, loin pain, nausea and, at times, sepsis - it is more serious and needs prompt medical review.

  • Do I need to be admitted to hospital?

    Not always. Well patients with mild disease may be treated with oral antibiotics and reviewed closely. Anyone with sepsis features, vomiting, pregnancy, a single kidney, immune suppression or an obstructed kidney should be admitted for intravenous treatment.

  • What antibiotics are used?

    Empirical intravenous options include co-amoxiclav, ceftriaxone or piperacillin-tazobactam, guided by NICE and local BSAC policy. Oral step-down to ciprofloxacin or trimethoprim is common once cultures and sensitivities return.

  • When is drainage needed?

    When the kidney is obstructed by a stone, tumour or scarring and infection has built up behind the blockage, drainage with a nephrostomy - see /treatments/nephrostomy-clinic/ - or a JJ ureteric stent is essential. Antibiotics alone will not clear an obstructed infected system.

  • How can I prevent recurrence?

    Stay well hydrated, treat any bladder infections promptly, review contraception and continence, and address underlying causes such as stones or obstruction. Specialist urology assessment helps if infections keep coming back.

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