--- title: "Kidney infection: Symptoms & Treatment | HealthAnswers" description: "Kidney infection (pyelonephritis) — symptoms, difference from cystitis, NHS antibiotics, and when to seek emergency care." url: https://healthanswers.co.uk/conditions/kidney-infection/ robots: noindex --- # Kidney infection: Symptoms & Treatment | HealthAnswers Health A–Z Kidney infection (pyelonephritis) — symptoms, difference from cystitis, NHS antibiotics, and when to seek emergency care. Written by HealthAnswers editorial team Medically reviewed by [HealthAnswers UK doctor review panel](https://healthanswers.co.uk/our-doctors/) Reviewed 3 July 2026 ## Quick answer What is kidney infection? A kidney infection (pyelonephritis) is a bacterial infection of the kidneys — usually when a bladder infection spreads upward. Symptoms include fever, flank pain (side of back), nausea, and urinary symptoms. Needs prompt antibiotics — often longer course than simple cystitis. Seek urgent care if very unwell, pregnant, or not improving on antibiotics — hospital IV treatment may be needed. General UK health information, not a diagnosis. In an emergency call 999 ; for urgent advice use [NHS 111](https://111.nhs.uk/) (GP out-of-hours in Northern Ireland). On this page 9 sections ## Key facts about kidney infection - Kidney infections are more serious than bladder infections (cystitis) — need longer antibiotic courses. - Classic symptoms — fever, shivers, pain in side/back, and pain urinating. - Women, pregnancy, diabetes, and kidney stones increase risk. - E. coli causes most cases — same bacteria as many UTIs. - Seek emergency care if unable to keep fluids down, confused, or severely unwell. ## Kidney infection — pyelonephritis A **kidney infection** (**acute pyelonephritis**) is **bacterial infection of the kidneys** — usually **E. coli** ascending from a **bladder infection ([UTI](https://healthanswers.co.uk/conditions/urinary-tract-infection/))**. It is **more serious than cystitis** — can cause **[sepsis](https://healthanswers.co.uk/conditions/sepsis/)** if untreated and occasionally **permanent kidney scarring**. ## Symptoms **Urinary (overlap with cystitis):** - pain or burning when urinating - frequency and urgency - cloudy or smelly urine - [blood in urine](https://healthanswers.co.uk/symptoms/blood-in-urine/) sometimes **Systemic — suggest kidney involvement:** - high [fever](https://healthanswers.co.uk/symptoms/high-temperature/) and rigors (shivering) - flank pain — aching side/back below ribs — one or both sides - [nausea](https://healthanswers.co.uk/symptoms/feeling-sick/) and vomiting - general malaise , fatigue **Severe:** - confusion (especially elderly) - [hypotension](https://healthanswers.co.uk/conditions/low-blood-pressure/) — sepsis **Men with UTI symptoms** — always investigate — may include **prostatitis**. ## Who is at risk - women — shorter urethra - pregnancy — higher risk and complications - diabetes - [kidney stones](https://healthanswers.co.uk/conditions/kidney-stones/) — obstruction - structural urinary tract abnormalities - catheter use - immunosuppression ## Diagnosis GP assessment: - history and examination — costovertebral angle tenderness (pain tapping back over kidney) - urine dipstick — nitrites, leukocytes, blood - midstream urine culture — identifies bacteria and [antibiotics](https://healthanswers.co.uk/treatments/antibiotics/) sensitivity - blood tests — CRP, WCC if systemically unwell - [pregnancy test](https://healthanswers.co.uk/tests/pregnancy-test/) in women of childbearing age **Imaging** ([ultrasound](https://healthanswers.co.uk/tests/ultrasound-scan/)/CT) if: - not improving on antibiotics - recurrent pyelonephritis - suspected abscess or stone ## Treatment ### Outpatient (moderate illness) **Oral antibiotics 7 to 14 days** — local guidelines; examples: - ciprofloxacin - co-amoxiclav - trimethoprim — only if sensitive on culture **[Paracetamol](https://healthanswers.co.uk/treatments/paracetamol/)/ibuprofen** — fever and pain **Fluids** — prevent dehydration ### Inpatient (severe) - IV antibiotics - fluids - monitoring for sepsis **Indications for hospital:** - vomiting unable to take oral antibiotics - pregnancy - sepsis signs - no improvement 48 hours oral - social factors — cannot manage at home ## When to worry during recovery Contact GP if: - fever persists >48 hours after starting antibiotics - worsening pain - new confusion - unable to urinate — obstruction May indicate **resistant organism**, **perinephric abscess**, or **stone**. ## Prevention of recurrence - complete antibiotic courses for UTIs - treat [constipation](https://healthanswers.co.uk/conditions/constipation/) — affects bladder emptying - good hydration - wipe front to back - pass urine after sex - investigate recurrent UTIs — ultrasound, urology **Cranberry products** — modest evidence for prevention — not treatment. ## Kidney infection in pregnancy **Always urgent** — increased risk of **premature labour** and **sepsis**. **Safe antibiotics** selected by specialist — never self-treat. ## Complications (rare with prompt treatment) - sepsis - kidney abscess - chronic pyelonephritis and scarring - papillary necrosis — diabetics Bladder infections are common; **fever plus [back pain](https://healthanswers.co.uk/symptoms/back-pain/)** upgrades urgency — same-day antibiotics prevent escalation to hospital admission. ## ! When to see a GP about kidney infection See a GP same day if you have fever with urinary symptoms or flank pain — kidney infection is suspected. Phone 111 out of hours. Go to A&E if severely unwell, confused, persistent vomiting, pregnant with UTI symptoms, or single kidney. Men with UTI symptoms always need assessment — kidney infection more common and may indicate prostate issue. ## Common questions about kidney infection What is the difference between a UTI and a kidney infection? Cystitis (bladder infection) causes pain urinating, frequency, and urgency — usually no high fever or back pain. Pyelonephritis (kidney infection) adds fever, chills, flank (side/back) pain, nausea, and feeling systemically unwell. Kidney infections need longer antibiotics and closer monitoring. How is a kidney infection treated? Oral antibiotics for 7 to 14 days if moderately unwell — often ciprofloxacin, co-amoxiclav, or others depending on local guidelines and allergies. Hospital admission with IV antibiotics if severe, pregnant, vomiting, or not responding. Urine culture guides choice when available. Can a kidney infection damage kidneys? Single treated episode rarely causes permanent damage in healthy people. Untreated or severe infection can scar kidneys — especially with repeated infections, obstruction (stones), or structural abnormalities. Follow-up if recurrent UTIs. How long does a kidney infection take to clear? Fever usually settles within 48 to 72 hours of starting correct antibiotics — finish full course even when better. Fatigue may linger a week. If not improving at 48 hours — contact GP; resistance or abscess possible. Can kidney infections recur? Yes — especially with kidney stones, incomplete bladder emptying, or anatomical problems. Women with recurrent UTIs may need investigation — ultrasound, urology referral. Prophylactic antibiotics sometimes used after specialist review. ## Sources - [NHS — Kidney infection](https://www.nhs.uk/conditions/kidney-infection/) - [NICE — UTI in adults](https://www.nice.org.uk/guidance/ng109) ## How we reviewed this page Medically reviewed by the [HealthAnswers UK doctor review panel](https://healthanswers.co.uk/our-doctors/) First published 14 June 2026 Medically reviewed 3 July 2026 Next review due 3 July 2029 or sooner if NHS or NICE guidance changes Written by HealthAnswers editorial team. Published by HealthAnswers (Elite Digital AI Solutions Ltd). [How we review content](https://healthanswers.co.uk/about/how-we-review/) · [Report a problem with this page](mailto:corrections@healthanswers.co.uk?subject=Problem%20with%3A%20Kidney%20infection&body=Page%3A%20https%3A%2F%2Fhealthanswers.co.uk%2Fconditions%2Fkidney-infection%2F%0A%0AWhat%20looks%20wrong%20or%20out%20of%20date%3A%0A)