Kidney Infections: Symptoms and Care

A kidney infection (pyelonephritis) is a bacterial infection of one or both kidneys. It usually starts as a lower urinary tract infection (UTI) in the bladder that travels upward. Kidney infections are more serious than simple cystitis and need prompt antibiotic treatment to prevent complications.

They're more common in women, partly because a shorter urethra makes it easier for bacteria to reach the bladder. Pregnancy, kidney stones, and anything that blocks the normal flow of urine also increase the risk.

Symptoms

Kidney infection symptoms tend to come on quickly, often over a few hours. You'll typically feel noticeably unwell, which is different from a simple bladder infection where you might just have discomfort during urination.

Common symptoms include pain in your back or side (usually on one side), high temperature, shivering, nausea or vomiting, and feeling generally unwell. You may also have symptoms of a lower UTI at the same time: burning or stinging when you urinate, needing to go frequently, and cloudy or strong-smelling urine.

In older adults, symptoms can be less obvious. Confusion, agitation, or a general decline in function may be the main signs, with fever sometimes absent.

Causes and risk factors

The bacterium E. coli causes the majority of kidney infections. It normally lives in the bowel, but if it enters the urinary tract and isn't cleared, it can ascend from the bladder to the kidneys.

You're at higher risk if you have a history of recurrent UTIs, are pregnant (the expanding uterus can compress the ureters and slow urine flow), have kidney stones or structural abnormalities of the urinary tract, have a weakened immune system, or use a urinary catheter.

Men develop kidney infections less often than women, but when they do, it may indicate an underlying prostate problem or urinary obstruction that needs investigating.

Diagnosis and treatment

Diagnosis is based on your symptoms, a physical examination, and a urine test. NICE guidelines recommend that a urine culture (a lab test that identifies the specific bacteria and which antibiotics will work against it) should be taken before starting antibiotics for suspected pyelonephritis.

Treatment is a course of antibiotics, typically for 7 to 14 days. The choice of antibiotic depends on local resistance patterns and your urine culture results. Most people can be treated at home with oral antibiotics, paracetamol for pain and fever, and plenty of fluids.

Hospital admission may be needed if you can't keep fluids or tablets down, if you're pregnant, if you have an underlying kidney condition, or if there's concern about sepsis. Intravenous antibiotics and fluids are given in these cases.

Prevention

Preventing kidney infections largely means preventing UTIs from developing or catching them early. Drink enough fluids so your urine stays pale. Don't hold in urine for long periods. Wipe front to back after using the toilet. Urinate after sexual intercourse.

If you're prone to recurrent UTIs, your GP may recommend low-dose prophylactic antibiotics, D-mannose supplements, or post-sex antibiotic prophylaxis depending on the pattern.

How we can help

We see patients with suspected kidney infections on the same day. A GP consultation (£150) includes a clinical assessment, urine dipstick and culture, and a prescription if infection is confirmed. If blood tests or imaging are needed, we can arrange these on-site.

For recurrent infections, we can investigate further with renal ultrasound and refer to a urologist if structural causes are suspected.