---
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.

## Who is this page for?

This page is for people in the UK who want a plain-English overview of Kidney infection, including when to seek help and what NHS care usually involves. It explains general information, not what is wrong with you personally.

## Who should skip this page?

Skip this page if you need a diagnosis, a prescription, or emergency care. It cannot replace a GP, pharmacist, NHS 111 or 999. If you are in immediate danger, call 999; for urgent advice that is not life-threatening, call 111 in England, Scotland or Wales, or use your GP out-of-hours service 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** 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 sometimes

**Systemic — suggest kidney involvement:**

- high fever and rigors (shivering)

- flank pain — aching side/back below ribs — one or both sides

- nausea and vomiting

- general malaise , fatigue

**Severe:**

- confusion (especially elderly)

- hypotension — 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 — 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 sensitivity

- blood tests — CRP, WCC if systemically unwell

- pregnancy test in women of childbearing age

**Imaging** (ultrasound/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/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 — 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** 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)