A urinary tract infection that has spread to the kidneys is a more serious condition than a lower UTI and requires prompt medical treatment. The symptoms change noticeably when bacteria travel up from the bladder to the kidneys, and recognising those changes is important because a kidney infection that is not treated quickly can lead to serious complications.
This article explains the key differences between a lower UTI and a kidney infection, what symptoms to watch for, and how urgently you need to act.
Can a Bladder Infection Spread to the Kidneys?
Yes. An untreated or inadequately treated lower UTI can allow bacteria to travel up the ureters, the tubes connecting the bladder to the kidneys, and cause a kidney infection, known clinically as pyelonephritis. This is more likely when a lower UTI is left without treatment, when treatment is inadequate or incomplete, or when there is an underlying factor such as a structural abnormality, kidney stones, or a weakened immune system that makes the urinary tract more vulnerable.
Not every UTI will spread to the kidneys; many resolve on their own before this happens. But the risk is real and is one of the key reasons prompt treatment of lower UTIs matters, particularly in pregnancy, when the risk of spread is higher.
Lower UTI vs Kidney Infection: How the Symptoms Differ
The symptoms of a kidney infection overlap with those of a lower UTI but include additional and more systemic signs that reflect the involvement of the kidneys. The table below sets out the key differences:
| Symptom | Lower UTI (bladder) | Kidney infection (upper UTI) |
| Burning or stinging when urinating | Yes | Often present |
| Frequent urge to urinate | Yes | Often present |
| Cloudy or strong-smelling urine | Yes | Often present |
| Lower abdominal pain or pressure | Common | May be present |
| Back or flank pain | Not typical | Common and often significant |
| High temperature (above 38°C) | Uncommon | Common |
| Shivering or rigours | Not typical | Common |
| Nausea or vomiting | Not typical | Common |
| Feeling severely unwell | Mild to moderate | Often marked |
The combination of lower urinary tract symptoms alongside back or flank pain, a high temperature, and feeling generally unwell is the classic presentation of a kidney infection and should prompt same-day medical contact rather than a wait-and-see approach.
Signs of a Kidney Infection That Need Same-Day Assessment
Contact your GP or NHS 111 the same day if you have symptoms that suggest a kidney infection. In particular, seek urgent help if you experience:
- Pain in your back, side, or groin alongside urinary symptoms
- A temperature above 38°C or shivering and chills
- Nausea or vomiting that is making it difficult to stay hydrated
- Blood in your urine alongside any of the above
- Symptoms that are rapidly worsening rather than staying stable
Call 999 or go to A&E if you develop confusion, extreme weakness, very rapid breathing, or feel significantly worse very quickly. These can be signs of urosepsis, a serious bloodstream infection originating from the urinary tract, which is a medical emergency.
Who Is Most at Risk of a UTI Spreading to the Kidneys?
Anyone can develop a kidney infection following a UTI, but certain groups are at higher risk:
- Pregnant women, in whom untreated UTIs carry a significantly elevated risk of spreading to the kidneys
- People with diabetes, whose immune response is less effective at containing infection
- Those with structural abnormalities of the urinary tract or a history of kidney stones
- People with a weakened immune system due to illness or immunosuppressive treatment
- Older adults, particularly men with an enlarged prostate, which can cause incomplete bladder emptying
- Anyone with a catheter in place
If you fall into any of these groups and develop urinary symptoms, seeking prompt medical assessment rather than managing symptoms at home is particularly important.
Kidney Infection Treatment: What to Expect
Kidney infections are treated with antibiotics, but unlike lower UTIs, they typically require a longer course and sometimes intravenous antibiotics in hospital if the infection is severe or the patient cannot tolerate oral medication due to vomiting.
Most people with a kidney infection who are otherwise well can be treated at home with a course of oral antibiotics prescribed by a GP. Rest and adequate hydration are important alongside antibiotic treatment. Pain and fever can be managed with paracetamol or ibuprofen, though ibuprofen should be used with caution if kidney function is a concern; your GP will advise.
If symptoms do not begin to improve within 24 to 48 hours of starting antibiotics, contact your GP or NHS 111 for further assessment. Completing the full antibiotic course is essential even if you feel better sooner.
Can a Pharmacist Help If You Suspect a Kidney Infection?
The NHS Pharmacy First service covers uncomplicated lower UTIs in eligible women aged 16 to 64. A kidney infection is outside the scope of this service and requires a GP assessment. If you suspect your symptoms have moved beyond a lower UTI, do not rely on the Pharmacy First route; contact your GP or NHS 111 directly.
A pharmacist can provide useful interim advice on hydration and symptomatic relief, and can help you identify whether your symptoms warrant urgent rather than routine attention. If in any doubt, a pharmacist is a sensible first call.
How Pharmacy To My Door Can Help
If you have been prescribed antibiotics for a kidney infection or ongoing treatment following a urinary tract infection, Pharmacy To My Door can manage your prescription and deliver it directly to your home. Our GPhC-registered pharmacy team is here to answer questions about your medication and ensure your prescription is handled accurately and promptly.
We deliver NHS and private prescriptions free across the UK.
Need a prescription managed after a kidney or urinary tract infection? Book an appointment with Pharmacy To My Door today. We deliver NHS prescriptions free across the UK.
Frequently Asked Questions (FAQ’s)
How quickly can a UTI spread to the kidneys?
There is no fixed timeline. An untreated UTI can spread within days in some people, or not at all in others. Prompt treatment of a lower UTI reduces the risk significantly.
What does a kidney infection feel like compared to a UTI?
A kidney infection adds back or flank pain, a high temperature, shivering, and nausea to the usual UTI symptoms. Feeling significantly and systemically unwell is the key distinguishing feature.
Can a kidney infection clear without antibiotics?
No. Kidney infections require antibiotic treatment. Delaying or avoiding treatment increases the risk of serious complications, including urosepsis. Always seek medical assessment if a kidney infection is suspected.
Should I go to A&E for a kidney infection?
Contact your GP or NHS 111 first for same-day advice. Go to A&E or call 999 if you develop confusion, extreme weakness, very rapid breathing, or deteriorate quickly, as these may indicate urosepsis.
Is a kidney infection dangerous during pregnancy?
Yes. Kidney infections in pregnancy carry a higher risk of complications and often require hospital treatment. Pregnant women with any urinary symptoms should seek prompt medical assessment.
