Kidney Infection
Also known as Pyelonephritis, Upper urinary tract infection
This article is general health information for the selected condition. It is not a diagnosis and does not replace clinical judgement. If you have questions or need treatment advice, please consult a qualified healthcare professional.
What is kidney infection?
A kidney infection happens when bacteria travel up from the bladder into one or both kidneys. It is considerably more serious than cystitis because it can damage the kidney and spread into the bloodstream. Back or flank pain with fever and urinary symptoms should be treated as a kidney infection until proven otherwise.
Causes
- Bacteria ascending from the bladder, usually E coli
- Urinary obstruction from stones or an enlarged prostate
- Vesicoureteric reflux allowing urine to travel back up
- Urinary catheters
- Bloodstream spread in rare cases
Symptoms
- Pain in the back or side below the ribs
- Fever and shivering
- Feeling generally very unwell
- Nausea and vomiting
- Burning on passing urine
- Needing to pass urine frequently and urgently
- Cloudy, bloody or foul smelling urine
- Confusion, particularly in older adults
Risk factors
- Female sex
- Recent urinary tract infection
- Kidney stones or urinary obstruction
- Pregnancy
- Diabetes
- Urinary catheter
- Weakened immune system
Diagnosis
- Urine dipstick and culture before antibiotics where possible
- Blood tests including inflammatory markers and kidney function
- Blood cultures if systemically unwell
- Ultrasound to look for obstruction or abscess
- CT scan where the diagnosis is unclear or recovery is slow
Treatment
- Antibiotics, usually for seven to fourteen days
- Intravenous antibiotics and admission if severely unwell or vomiting
- Adequate fluids and pain relief
- Urgent drainage if the kidney is obstructed and infected
- Investigation for underlying stones or obstruction afterwards
Self care
- Complete the full antibiotic course even once you feel better
- Drink plenty of fluids unless told otherwise
- Take paracetamol for pain and fever
- Rest until the fever settles
- Avoid anti inflammatory painkillers, which can stress the kidneys
- Empty the bladder fully and regularly
- Seek review if you are not improving within 48 hours
When to see a doctor
Book an appointment if:
- Urinary symptoms with back or flank pain
- Fever alongside urinary symptoms
- Symptoms not improving after 48 hours of antibiotics
- Recurrent kidney infections
- Any urinary infection in pregnancy
- Kidney infection symptoms in a man, which needs investigation
Some symptoms need emergency care rather than an appointment. See the warning signs listed above.
Prevention
- Treat bladder infections promptly
- Drink enough fluid through the day
- Empty the bladder fully and after sex
- Wipe front to back
- Treat kidney stones and prostate enlargement
- Vaginal oestrogen after menopause for recurrent infections
Outlook
Most kidney infections respond well to prompt antibiotics with full recovery. Delay or obstruction raises the risk of kidney abscess, permanent scarring and sepsis. Recurrent infections warrant investigation for an underlying structural cause, since repeated episodes can cause lasting kidney damage.
Common questions
How is this different from a bladder infection?
Cystitis causes burning and frequency without fever or back pain, and is usually treated with three days of antibiotics. A kidney infection adds fever, flank pain and feeling systemically unwell, and needs a longer course and closer follow up.
Why does it need urgent attention in pregnancy?
Kidney infection in pregnancy carries a higher risk of preterm labour and of the infection spreading to the bloodstream. It is usually assessed the same day and often treated in hospital.
References
Important: Dard AI is not a medical device and does not diagnose, treat, or replace clinician judgement. This article is general information only. Always consult a qualified healthcare professional about diagnosis and treatment, and seek emergency care for severe or rapidly worsening symptoms.