A kidney infection—also known as pyelonephritis—is a type of urinary tract infection that occurs when bacteria enter your body. The urinary tract is your body’s system for removing urine from the body. Urine flows from the kidneys, ureters, bladder, and urethra, and then out of your body. Infections to any part of the tract are called urinary tract infections, or UTIs.

Generally, infections like UTIs are more common in the lower part of the urinary tract, which includes the urethra and bladder. But sometimes, infections can rise up to the ureters and into the kidneys, causing pyelonephritis to occur. About 1 in 30 cases of UTIs lead to a kidney infection.¹

Typically, you only experience kidney infection symptoms after you’ve had initial symptoms from a lower urinary tract infection. If you develop a UTI, it’s common to feel an urgency to use the bathroom and feel a burning sensation when you pee. If the UTI worsens and turns into a kidney infection, you’ll likely experience symptoms like a fever and back pain.²

Flank Pain

Flank pain is one of the hallmark symptoms of a kidney infection. This type of pain refers to tenderness and discomfort on your sides. In some cases, the pain can travel down to your groin.³

It’s important to note that flank pain can help you distinguish a potential kidney infection from a lower UTI. If you have a lower urinary tract infection that hasn’t spread to your kidneys, you are unlikely to experience flank pain.⁴

If your infection does travel up to your kidneys, it’s common to have pain on one side of the body. In addition to the pain, it may also hurt to touch the area where flank pain is occurring and your stomach may also feel tender. In most cases, the pain is gradual and feels like a dull pain, rather than a sharp or stabbing pain.⁵

Infection Symptoms

It’s common to experience general infection symptoms when you develop a kidney infection. Most people with a kidney infection have a high fever—sometimes as high as 103 degrees Fahrenheit or more. You might also experience chills, fatigue, nausea, and a general feeling of being unwell, which is a symptom known as malaise.³⁶ Keep in mind: chills and fever symptoms are much less likely to occur from a lower UTI in your bladder or urethra.

While less common, a kidney infection may also cause symptoms such as dizziness, low blood pressure, and an elevated heart rate. It’s important to keep track of the symptoms you’re experiencing and get treatment as soon as you can.

This is because if a kidney infection is left untreated, the infection can spread beyond the urinary tract and into the blood. If this happens, you might experience a life-threatening complication known as sepsis, which causes symptoms such as very low blood pressure, organ damage, and sometimes death.⁶

Urinary Changes

Many people with a kidney infection notice changes in their urination. You might have one or more of the following symptoms:³

• Dysuria, or a burning or painful sensation when you pee
• Peeing frequently
• Having an urgency to pee even if you don’t have to go
• Dark, smelly, bloody or cloudy urine

Keep in mind: these symptoms can occur even if you have a lower UTI that hasn’t spread to the kidneys just yet. However, if you experience urinary changes with flank pain and other infection-related symptoms, it’s best to talk to your healthcare provider about your treatment options.⁴

Symptoms in Children

Generally, children over the age of five tend to experience similar kidney infection symptoms as adults. However, kidney infections and UTIs are often more difficult to diagnose in younger children. This may occur because children may not always know how to describe the pain they are feeling.

If you suspect your child might have a kidney infection or lower UTI, it may be helpful to also check for additional symptoms that children with kidney infections can experience, including:⁷

• Poor appetite or trouble feeding
• Lack of energy
• Low-grade fever

These symptoms are not always exclusive to a kidney infection, however. If you notice a change in your child’s health, talk to their pediatrician or other primary care provider to learn more about what might be causing their symptoms.

Symptoms in Older Adults

In addition to the hallmark kidney infection symptoms, older adults are also at risk of developing psychological and cognitive changes. This may include confusion, trouble thinking, issues with memory, or a change in mood. Even in adults who are cognitively sharp, psychological changes can occur quickly during an infection.

It’s important to note that these changes are temporary. However, older adults or their caregivers should still seek treatment to improve symptoms and prevent further complications from occurring.²

When to See a Healthcare Provider

Without treatment, kidney infections can cause complications that can worsen your health. If you notice changes to your urinary patterns, experience infection-related symptoms, or have flank pain, it’s essential to see your healthcare provider as soon as you can.⁶

You should also see a healthcare provider if you’ve been diagnosed with a lower UTI, but your symptoms haven’t improved, or if you have worsening symptoms. Your provider can prescribe you a different antibiotic to treat the infection or help you understand alternative options for treatment.

A Quick Review

A kidney infection—also known as pyelonephritis—is a type of urinary tract infection (UTI). Kidney infections develop in a minority of people who first get lower UTIs that affect the urethra or bladder. Those who develop kidney infections will experience UTI-related symptoms such as changes in urination. However, if symptoms such as fever or pain arise, they infection may have spread to the kidneys.

Kidney infections can cause extreme pain and discomfort. Without treatment, complications can occur. That’s why seeing your healthcare provider if you notice a change in your symptoms is essential as they can help you figure out the treatment that is right for you.

Sources:

1. American Urological Association. Kidney (renal) infection—Pyelonephritis.
2. Belyayeva M, Jeong JM. Acute pyelonephritis. In: StatPearls. StatPearls Publishing; 2023.
3. National Institute of Diabetes and Digestive and Kidney Diseases. Symptoms & causes of kidney infection (pyelonephritis).
4. Li R, Leslie SW. Cystitis. In: StatPearls. StatPearls Publishing; 2023.
5. Varma PP, Varma E, Bajpai G. An unusual case of right flank pain. Am J Kidney Dis. 2021;78(1):A12-A14. doi:10.1053/j.ajkd.2020.10.022
6. Herness J, Buttolph A, Hammer NC. Acute pyelonephritis in adults: Rapid evidence review. Am Fam Physician. 2020;102(3):173-180.
7. Simões E Silva AC, Oliveira EA, Mak RH. Urinary tract infection in pediatrics: an overview. J Pediatr (Rio J). Suppl 1(Suppl 1):65-79. doi:10.1016/j.jped.2019.10.006

8. Preminger GM, Curham GC. Patient education: Kidney stones in adults. In: O’Leary, MP, Lam AQ, eds. UptoDate. UptoDate; 2023.

Important Notice: This article was also published at www.health.com by Ruth Jessen Hickman, MD where all credits are due. Medically reviewed by Anju Goel, MD, MPH

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