Kidney Infection Symptoms: Common Causes, Related Conditions, and When to See a Doctor

Kidney infection symptoms commonly include fever, chills, pain in the back or side, nausea, and urinary changes such as burning, urgency, or cloudy urine. Because a kidney infection can worsen quickly, these symptoms should be assessed promptly by a qualified doctor.

Overview: What kidney infection symptoms usually feel like

Kidney infection symptoms often begin with signs of a urinary tract infection and then become more intense as the infection reaches one or both kidneys. Many people notice burning or pain during urination, needing to urinate more often, or urine that looks cloudy or smells unusually strong. When the kidneys are involved, these urinary symptoms are often joined by fever, chills, pain in the side or back, nausea, or vomiting.

A kidney infection is also called pyelonephritis. It is more serious than a simple bladder infection because the kidneys help filter waste and maintain fluid balance. Prompt treatment is important to relieve symptoms, clear the infection, and reduce the risk of complications such as spreading infection or kidney damage.

Symptoms can vary from person to person. Some people have obvious urinary symptoms, while others mainly feel unwell, feverish, tired, or have pain under the ribs on one side. Older adults may sometimes have less typical symptoms, such as confusion or general weakness, which is one reason medical evaluation should not be delayed.

Common symptoms and warning signs

The most common kidney infection symptoms include fever, chills, pain in the flank area, and changes in urination. The flank is the area on either side of the lower back, just below the ribs. This pain may be dull, constant, or sharp, and it may affect one side or both sides.

Urinary symptoms often overlap with symptoms of a bladder infection. A person may feel burning when urinating, an urgent need to urinate, frequent urination in small amounts, or pressure in the lower abdomen. Urine may appear cloudy, dark, or blood-tinged, and some people notice a strong or unpleasant odor.

Whole-body symptoms can help distinguish a kidney infection from a milder lower urinary infection. These may include:

• Fever or feeling feverish
• Chills or shaking
• Nausea or vomiting
• Fatigue or feeling generally unwell
• Loss of appetite
• Side, back, or upper abdominal pain

Children, older adults, and people with weakened immune systems may not always describe classic symptoms. In these groups, unexplained fever, poor feeding, confusion, lethargy, or worsening overall health may be the first clues.

Why kidney infections happen and who is at higher risk

Most kidney infections happen when bacteria enter the urinary tract through the urethra, multiply in the bladder, and then travel upward through the ureters to the kidneys. For this reason, a kidney infection often develops as a complication of a urinary tract infection. Less commonly, bacteria can reach the kidneys through the bloodstream from another infection elsewhere in the body.

Anything that slows urine flow or makes it easier for bacteria to remain in the urinary tract can raise the risk. Examples include kidney stones, an enlarged prostate, structural differences in the urinary tract, vesicoureteral reflux, or use of a urinary catheter. Some people are also more likely to have repeated infections because of conditions that affect the immune system or bladder emptying.

Risk tends to be higher in women because the urethra is shorter, making it easier for bacteria to reach the bladder. Pregnancy can also increase risk because hormonal and physical changes may slow urine drainage. Other factors include diabetes, recent urinary procedures, dehydration, a history of recurrent UTIs, and conditions that affect nerve signals to the bladder.

Related conditions may overlap or contribute to symptoms. For example, a person with kidney stones may have severe side pain and blood in the urine, while an infection can develop if urine flow is blocked. Distinguishing these conditions matters because treatment needs can differ.

How doctors diagnose a kidney infection

Diagnosis starts with the pattern of symptoms, a medical history, and a physical examination. A doctor will usually ask about fever, urinary symptoms, nausea, side or back pain, recent urinary infections, pregnancy, kidney stones, catheter use, or any underlying health conditions that might raise risk.

Urine testing is central to diagnosis. A urinalysis can look for signs of infection such as white blood cells, bacteria, nitrites, or blood. A urine culture may be used to identify the bacteria causing the infection and help guide antibiotic choice, especially if symptoms are severe, recurrent, or not improving as expected.

Blood tests may be recommended if the person appears more unwell, has a high fever, is dehydrated, or there is concern that the infection may have spread. Imaging tests are not always needed, but they can be helpful when symptoms are severe, there is suspicion of blockage, kidney stones, or an abscess, or when the diagnosis is uncertain. In selected cases, doctors may use MRI or CT scanning to look more closely at the kidneys and urinary tract.

Treatment options and what recovery may involve

Kidney infections are usually treated with antibiotics, along with fluids, rest, and symptom support. The exact treatment depends on how severe the infection is, the person’s age and general health, whether they are pregnant, and whether there are complications such as vomiting, dehydration, or an obstruction in the urinary tract.

Some people can be treated at home with oral antibiotics and careful follow-up. Others may need hospital care, especially if they cannot keep fluids down, have severe symptoms, are pregnant, have significant underlying illness, or show signs that the infection may be spreading. Intravenous fluids and antibiotics may be needed in these situations.

If an underlying problem is contributing to the infection, treatment should address that as well. For example, a blockage caused by stones or another structural issue may need further evaluation and management. Where a complicated urinary problem is suspected, specialists may recommend a focused urology evaluation to help prevent repeat infections and protect kidney function.

Many people begin to feel better within a few days of starting treatment, but it is important to complete the prescribed antibiotic course and attend follow-up if advised. Stopping treatment early can allow the infection to return or become harder to treat.

Prevention and self-care after symptoms start

Self-care cannot cure a kidney infection, but it can support recovery while medical treatment is underway. Drinking enough fluids, unless a doctor has advised otherwise, may help maintain hydration. Rest is also important, especially if fever, chills, or fatigue are present. Over-the-counter pain relief may help some people, but any medication should be used as directed and discussed with a doctor when there are kidney concerns.

Preventing future infections often begins with reducing the chances of bacteria staying in the urinary tract. Helpful measures may include not delaying urination, drinking fluids regularly, urinating after sexual activity if prone to UTIs, and following catheter-care instructions carefully when relevant. People with recurring infections may need a more individualized prevention plan.

It is also sensible to seek evaluation for repeated urinary symptoms rather than self-treating repeatedly. Recurrent infections can signal an underlying issue such as a stone, incomplete bladder emptying, or another urinary tract problem. If symptoms are frequent or complex, a doctor may suggest more detailed testing, sometimes including ultrasound to assess the kidneys and bladder.

When to seek medical care

Kidney infection symptoms should be assessed promptly, particularly when fever, flank pain, nausea, or vomiting occur together with urinary symptoms. A person should not wait to see whether symptoms settle on their own if they suspect the infection may have reached the kidneys.

Urgent medical care is especially important if there is high fever, severe side or back pain, repeated vomiting, confusion, fainting, trouble keeping fluids down, very little urine output, or symptoms of sepsis such as rapid breathing, marked weakness, or feeling suddenly much worse. Pregnant individuals, young children, older adults, and people with diabetes, kidney disease, or weakened immunity should seek care early because complications can develop more quickly.

If symptoms of a bladder infection are getting worse instead of better, or if they return soon after treatment, medical review is also important. Near the end of the care pathway, some patients may benefit from multidisciplinary assessment; Acibadem International’s specialists at JCI-accredited hospitals diagnose and treat kidney infections and related urinary conditions for international patients.

Frequently asked questions

What are the first signs of a kidney infection?

Early signs may include burning with urination, needing to urinate often, cloudy urine, or an urgent need to urinate. As the infection reaches the kidneys, fever, chills, side or back pain, nausea, and feeling generally unwell often develop.

How is a kidney infection different from a bladder infection?

A bladder infection usually causes lower urinary symptoms such as burning, urgency, and frequent urination. A kidney infection often adds fever, chills, back or side pain, nausea, or vomiting, which suggest the infection has moved higher in the urinary tract.

Can kidney infection symptoms go away without treatment?

Symptoms may sometimes seem to improve temporarily, but a true kidney infection should not be left untreated. Medical treatment is important because the infection can worsen or spread and may lead to complications.

When should someone go to urgent care or the emergency department?

Urgent care is appropriate when kidney infection symptoms include fever, flank pain, vomiting, or worsening urinary symptoms. Emergency evaluation is especially important for severe pain, confusion, dehydration, fainting, very little urine, or possible signs of sepsis.

Can a kidney infection cause blood in the urine?

Yes, some people with a kidney infection notice blood in the urine, either visible or detected on a test. Blood in the urine can also happen with other conditions, such as stones, so it should be medically assessed.

Who is more likely to get a kidney infection?

Risk is higher in people who have frequent urinary tract infections, kidney stones, urinary blockage, catheters, diabetes, pregnancy, or problems emptying the bladder. Women are also more commonly affected because bacteria can reach the bladder more easily.

References

• National Institute of Diabetes and Digestive and Kidney Diseases
• Mayo Clinic
• Merck Manual Consumer Version
• Centers for Disease Control and Prevention
• American Urological Association

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.