Overview
A kidney infection is a type of urinary tract infection (UTI) that affects one or both kidneys. It is more serious than an infection that stays in the bladder. The medical name is pyelonephritis.
Most are caused by bacteria that infect the bladder and then travel up to a kidney. With prompt treatment most people recover fully. If it is left untreated it can be serious, and sepsis is the main danger.
Symptoms
Symptoms can include:
- A high temperature, with shivering and feeling hot, cold or shaky
- Pain in the lower back or side, or in the groin
- Feeling or being sick
- Aching muscles and feeling generally unwell
- Pain or stinging when passing urine, and needing to go more often or more urgently
- Dark or cloudy urine
- Diarrhoea
Young children may wet themselves or seem drowsy, and a child under 2 may only have a high temperature. In older people, new confusion may be the only sign.
When to see a doctor
Get medical help the same day for a very high temperature or shivering, pain in the back or side, vomiting, blood in the urine, or if you have not passed urine all day. The same applies to anyone who is pregnant, an older adult, a young child, or has diabetes, kidney stones or a weakened immune system. See a doctor too if symptoms have not cleared after , or if they return soon after treatment.
Causes
Kidney infections are caused by bacteria entering the urinary tract and moving up to the kidneys. They are often a complication of a bladder infection (cystitis), though they can happen without one.
Kidney stones, changes in the shape of the urinary tract and a recent operation on the urinary tract make it easier for bacteria to reach the kidneys.
Risk factors
- Being a woman, as kidney infections are more common in women, though anyone can get one
- Pregnancy
- Kidney stones or changes in the structure of the urinary tract
- Recent surgery on the urinary tract
- Diabetes or other long-term health conditions
- A weakened immune system
Complications
Early treatment prevents most complications. When treatment is late or the infection returns, they can include:
- Sepsis, a life-threatening reaction to infection. The risk is higher in young children, very old adults and people with a weakened immune system
- Kidney damage or scarring
- Repeated kidney infections
Prevention
- Drinking plenty of fluids through the day (ask a doctor how much if you have kidney problems)
- Emptying the bladder fully when you pass urine
- Not holding on when you feel the urge to go
- Getting urine symptoms checked rather than waiting for them to settle
Diagnosis
A doctor will ask about your symptoms, examine you and test a urine sample to confirm the infection. Blood tests may be done as well.
Imaging tests, such as an scan, may be used to look for a cause, for example a kidney stone or a blockage.
Treatment
Most people are treated with antibiotic tablets, usually for one to two weeks. Take the full course even if you feel better. Rest and drink plenty of fluids.
People who are very ill, cannot take tablets or drink enough, are pregnant, are older, or have long-term conditions or kidney stones may need hospital treatment, with and fluids through a drip. A hospital stay is usually a few days to a week.
Paracetamol can ease fever and pain. Avoid ibuprofen unless a doctor advises it. Most people feel better after about two weeks, though older people and those with other conditions may take longer.
Myths and facts
Things people often say about this. Open each one to see what is true.
Myth“A kidney infection is just a bad bladder infection and will go away on its own.”What is true?
Fact
A kidney infection is more serious than a bladder infection. If it is not treated it can lead to sepsis, a life-threatening reaction to infection, and can damage or scar the kidneys. It needs antibiotics prescribed by a doctor.
Myth“I can stop the antibiotics once the fever and pain are gone.”What is true?
Fact
Symptoms ease before the infection is fully cleared. Finish the whole course even if you feel better, because stopping early may let the infection come back and be harder to treat.
Myth“Ibuprofen is the best medicine for the pain and fever.”What is true?
Fact
NHS advice is that paracetamol can reduce fever and pain, and that ibuprofen should be avoided unless a doctor advises it, as it may increase the risk of further kidney problems.
Myth“Drinking lots of water or cranberry juice will wash the infection out.”What is true?
Fact
Drinking plenty of fluids is advised during treatment, but it does not replace antibiotics. Diet and nutrition are not thought to prevent or treat kidney infections.
Questions to ask your doctor
Tick the ones you want answered and take them with you.
Common questions
How is a kidney infection different from a bladder infection?
A bladder infection (cystitis) stays in the bladder and mostly causes burning and frequent trips to the toilet. A kidney infection has reached the kidneys, so there is usually fever, back or side pain and feeling unwell. It is more serious and needs prompt treatment.
How long does it take to recover?
Symptoms may take a week or longer to settle after treatment starts. Most people feel better after about two weeks, though older people and those with other health conditions may take longer. Rest, and ask your doctor when you can go back to work.
Can a kidney infection damage my kidneys?
Early treatment prevents most complications. If an infection is left untreated, or keeps coming back, it can scar or damage the kidneys, and it can lead to sepsis.
Can I take ibuprofen for the pain and fever?
NHS advice is to avoid ibuprofen unless a doctor advises it, because it may increase the risk of further kidney problems. Paracetamol is the usual choice for fever and pain, but check with a doctor or pharmacist, especially for a child.
