01 · Overview
The short version
A kidney infection is a UTI that has moved higher
It starts in the urinary tract, but the infection has reached the kidneys instead of staying in the bladder. That is why people can have fever, chills, nausea, or pain in the back or side below the ribs.
Pain location helps, but it does not prove the cause
Flank or back pain can happen with kidney infection, but it can also come from a kidney stone, muscle strain, shingles, or other problems. Urine testing helps sort out the cause.
Antibiotics are the main treatment
Kidney infections are usually treated with antibiotics. Some people can be treated at home if they are stable, while others need IV medicine or hospital care if they are very sick or cannot keep fluids down.
Some situations need faster action
Pregnancy, diabetes, poor bladder drainage, a catheter, immune suppression, and recurrent UTIs make a kidney infection more concerning and more likely to need prompt medical review.
02 · Care guidance
When to get help
Emergency help
- Call 911 or go to the emergency room now if fever comes with severe weakness, confusion, trouble breathing, fainting, severe vomiting, or signs of sepsis such as a very fast heartbeat and very low blood pressure.
- Get emergency care right away if you are pregnant and have fever plus back or side pain.
- Seek emergency care now for sudden severe one-sided pain with vomiting, especially if a kidney stone or another urgent problem is possible.
- Children with fever, vomiting, back or side pain, or urinary symptoms need prompt medical assessment because kidney infections can be harder to recognize in kids.
Get advice promptly
- Contact a clinician the same day if you have burning with urination plus fever, back or side pain, chills, nausea, or worsening symptoms after a recent bladder infection.
- Get prompt medical advice if symptoms keep coming back, if you are male, if you have diabetes, if you are immunocompromised, or if you have been told you may have urinary tract blockage or kidney disease.
If you have mild urinary symptoms without fever or flank pain, arrange a non-urgent visit for urine testing and guidance before the problem has a chance to move upward.
03 · Kidney Infections
What makes this more than a bladder infection
A kidney infection is a urinary infection that has moved up to the kidneys, so the symptom pattern is usually broader than simple burning with urination.
The urinary system includes the kidneys, ureters, bladder, and urethra. When germs reach the kidneys, the illness is often called a kidney infection or pyelonephritis. Because the kidneys sit near the middle of the back below the rib cage, the pain is often felt in the flank rather than only in the lower belly.
That location can be misleading. Back or side pain can also come from muscle strain, a stone, shingles, or another abdominal or pelvic problem. The difference is that kidney infection is more likely to bring fever, chills, tiredness, nausea, vomiting, or a general feeling of being ill along with urinary symptoms.
- Burning, urgency, or lower belly pressure can happen with either bladder or kidney infection.
- Fever, chills, nausea, and flank pain make kidney involvement more likely.
- Urine testing is often needed because symptoms overlap with other causes.
04 · Kidney Infections
Symptoms that point toward the kidneys
Fever plus urinary symptoms is the big warning pattern, but it still does not rule out stones or other causes.
Common urinary symptoms include burning when you urinate, needing to urinate often, lower belly pressure, cloudy or reddish urine, or urine that smells bad. When the infection reaches the kidneys, fever, shaking, chills, nausea, vomiting, back or side pain below the ribs, and marked tiredness are more concerning.
It helps to pay attention to the whole picture. A kidney stone can cause severe one-sided pain and vomiting. Muscle strain can hurt more with movement or when lying in a certain position. If you also have vaginal or pelvic pain, the cause may be outside the urinary tract. That is why symptoms are used to decide urgency, not to make a final diagnosis.
- Burning with urination can happen before kidney symptoms appear.
- Fever, chills, or feeling very ill makes same-day care more important.
- Blood in urine can happen with infection or stones and should be checked.
05 · Kidney Infections
Who needs extra caution
Certain health conditions or life stages make a kidney infection more dangerous or harder to manage.
People of any age or sex can get urinary tract infections, but women get them more often overall. Risk is higher when bacteria can reach the urinary tract more easily or when urine does not drain well.
Known risk factors include diabetes, a tube used to drain the bladder, spinal cord injury, trouble emptying the bladder, urinary blockage, pregnancy, and a history of frequent UTIs. A weakened immune system can also make infection harder to clear. Men with urinary symptoms also deserve prompt evaluation because UTIs are less common in men and may point to an underlying problem.
- Pregnancy changes how urgently urinary symptoms should be handled.
- Recurrent UTIs should be checked for a cause such as blockage or poor bladder emptying.
- A catheter or spinal cord injury can raise the chance of infection.
06 · Kidney Infections
What happens at the visit
Clinicians usually start with your symptoms and a urine test, then add more testing if the case looks complicated.
At the visit, expect questions about fever, pain, nausea, urine changes, recent UTIs, pregnancy, and any urinary tract problems. A urine test helps look for infection. If the pattern is severe, unusual, or not improving, a urine culture may be ordered to identify the germ and help choose the right antibiotic.
Blood tests may be used if you look very ill or if kidney function needs to be checked. Imaging is more likely when the pain is intense, one-sided, or paired with repeated vomiting, persistent fever, or concern for a stone or blockage. The point of the visit is not just to label the problem, but to make sure the treatment matches how sick you are.
- Bring a list of symptoms and recent medicines.
- Tell the clinician if you are pregnant or could be pregnant.
- Ask whether urine culture or imaging is needed in your case.
07 · Kidney Infections
Treatment and recovery
Antibiotics treat the infection, but some people need fluids, pain control, or hospital care if they are too sick for oral treatment.
Kidney infections are usually treated with antibiotics. Some people can be treated at home if they are stable and able to drink fluids, while others need IV antibiotics or hospital treatment, especially if they have severe vomiting, dehydration, pregnancy, or signs of a serious infection. Pain and fever control may also be part of care.
Recovery is not always instant. Fever and pain should start to improve, but you should seek follow-up if symptoms worsen, you cannot keep fluids down, or you develop confusion or weakness. It is important to take antibiotics exactly as prescribed and not stop early just because you feel better.
- Do not use leftover antibiotics or someone else’s medicine.
- Drink fluids if you can keep them down, but do not force large amounts if you are vomiting.
- Worsening symptoms after starting treatment need reassessment.
08 · Kidney Infections
Why this infection is treated quickly
Delays can let the infection spread, cause dehydration, or lead to a more serious illness.
Kidney infections are treated faster than a simple bladder infection because they can become more serious. The infection can worsen, spread into the bloodstream, or make you too sick to drink enough fluids. Some people also develop temporary kidney function problems during a severe illness.
That is why fever with urinary symptoms should not be brushed off. Waiting several days to see if it goes away on its own can delay the right treatment and make the illness harder to manage. Prompt care helps decide whether oral antibiotics are enough or whether stronger treatment is needed.
- Sepsis is a medical emergency.
- Pregnancy with fever and flank pain needs urgent evaluation.
- Severe vomiting, confusion, or fainting should not wait for an office visit.
09 · FAQ
Questions people ask
Can a kidney infection go away on its own?
No. Kidney infections usually need antibiotics, and waiting can make the illness more serious. Even mild urinary symptoms without fever should still be checked soon, because treatment is easier before the infection moves higher.
Does back pain always mean kidney infection?
No. Back or flank pain can come from muscle strain, a kidney stone, shingles, or other causes. Kidney infection is more likely when the pain happens with fever, chills, burning with urination, nausea, or vomiting.
Will I need a CT scan or ultrasound?
Not always. Many kidney infections are diagnosed with symptoms and a urine test. Imaging is more likely if the pain is severe, the infection seems complicated, you are not improving, or the clinician is worried about a stone or blockage.
Why do doctors sometimes ask for a urine culture?
A urine culture helps identify the bacteria causing the infection and can show which antibiotics are likely to work. It is especially helpful if symptoms are severe, keep coming back, or do not improve as expected.
Is a kidney infection the same as kidney disease?
No. A kidney infection is an infection, usually from bacteria. Kidney disease is a broader term for problems that damage kidney function over time or suddenly. They are different, although a severe infection can temporarily affect kidney function.
What should I do while waiting to be seen?
If you have symptoms that suggest a kidney infection, do not delay care. Drink fluids if you can keep them down, rest, and avoid leftover antibiotics or someone else’s medicine. If you develop fever, worsening pain, vomiting, confusion, or weakness, seek urgent care right away.
10 · References
References and supporting evidence
These sources support the points identified below. Source checking is not clinical approval.
- S1: Urinary Tract InfectionsMedlinePlus / U.S. National Library of Medicine
Explains common urinary infection symptoms and that a urine test is used to check for UTI; also supports antibiotic treatment and higher risk with diabetes, bladder drainage tubes, and spinal cord injury.
- S2: Kidney DiseasesMedlinePlus / U.S. National Library of Medicine
Explains kidney location, which helps describe flank pain, and supports the broader distinction between kidney infections and other kidney diseases, along with blood and urine testing for kidney problems.
General information, not a diagnosis. This guide is not a substitute for care from a qualified healthcare professional. For an emergency, call 911 in the US or your local emergency number. Illustrations are conceptual and are not diagnostic images.