Kidney Infections: Signs, Symptoms and Treatment

By Zina Semenovskaya, MD
Medically reviewed checkmarkMedically reviewed
September 10, 2020

When a kidney infection occurs, it’s important to recognize and treat it promptly in order to prevent long-term health effects. Our kidneys play multiple important roles in keeping us healthy. Kidneys filter waste and fluids from our blood while simultaneously producing hormones that help regulate our blood sugar, make red blood cells (which carry oxygen throughout our body), and keep our bones strong. It’s no wonder we need healthy, functioning kidneys!

What Is a Kidney Infection?

A kidney infection, formally called “pyelonephritis”, is a bacterial infection of one or both kidneys. Our kidneys are part of our urinary tract, which also contains the urethra, bladder, and ureters. Kidney infections are considered a common type of urinary tract infection (UTI). Due to differences in anatomy, Kidney infections tend to affect women more than men. In the US, it is estimated that 15-17 women out of 10,000 are affected by kidney infections annually, while 3-4 men out of 10,000 suffer from them.

What Causes a Kidney Infection?

A kidney infection typically occurs when an existing UTI, specifically a bladder infection (also called “cystitis”), spreads to the kidneys. The same bacteria that cause most bladder infections, Escherichia Coli (E Coli), are responsible for 90% of kidney infections. Treating UTIs promptly can prevent a kidney infection, but unfortunately sometimes UTI symptoms are subtle, and other times people develop a bladder and kidney infection at the same time.

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How Do I Know If I Have a Kidney Infection?

Kidney infections often develop quickly. Typical symptoms include:

Since a bladder infection often causes and may occur simultaneously with a kidney infection, some of the symptoms can overlap. It’s also worth noting that symptoms of a kidney infection tend to vary according to age. Young children under the age of two may only experience a fever, or may cry when urinating. Meanwhile, adults 65 years or older may experience confusion or other changes in their mental status, while not exhibiting a fever or other symptoms.

How Is a Kidney Infection Diagnosed?

After listening to your symptoms, your doctor will likely ask whether you’ve had a recent bladder infection. A physical exam will be performed to evaluate for pain in your flanks and abdomen. If you’re female, a pelvic exam may be performed if you are pregnant or if you report other concerning symptoms such as vaginal discharge.

If your doctor suspects an infection, a urine test will be done, called a urinalysis. This simple test detects the presence of bacteria and other factors that determine whether you have an active infection. The urine can then be sent for additional testing to determine the type of bacteria and help direct the most specific antibiotic treatment. Occasionally, if you exhibit severe symptoms, bloodwork may be done for additional evaluation.

Sometimes, imaging tests are done to evaluate for other conditions. Ultrasound and CT scans are commonly used to evaluate for kidney stones, bowel problems, and other medical conditions as determined by your doctor.

Kidney Infection Risk Factors

The following factors may increase a person’s risk of developing a kidney infection:

  • Female anatomy: The shorter length of a woman’s urethra, and its proximity to the vagina and anus, makes women more prone to urinary tract infections.
  • Pregnancy: 2% of women develop a kidney infections during pregnancy due to changes in the size of the uterus, which can compress the ureters, reducing urinary flow and making it easier for bacteria to infect the urinary tract. It is especially important to treat a kidney infection during pregnancy to prevent complications.
  • Blockage of the urinary tract: A large, obstructing kidney stone or an enlarged prostate can create a mechanical blockage of your urinary tract, causing a back up in urinary flow tor limits your ability to fully empty your bladder presents you with a higher risk of developing bladder and kidney infection.
  • Weak immune system: Certain medical conditions, such as diabetes and HIV, can impair a person’s immune system, making them more likely to develop infections and complications from them.

Treating Kidney Infections

The length of treatment for a kidney infection depends on the severity of the infection and the patient’s overall health and other medical conditions. Kidney infections are generally treated with antibiotics, either orally or intravenously in the hospital.

Kidney infections may be considered “uncomplicated” or “complicated.” Here’s the difference:

  • Uncomplicated infection: Patients who are generally healthy and therefore highly unlikely to experience any serious complications from their kidney infection.
  • Complicated infection: High-risk patients who are more likely to suffer complications due to other medical conditions or age.

Depending on the severity of the kidney infection, you can either be treated at home with oral antibiotics or with an IV at the hospital or in a day treatment clinic. The antibiotic treatment usually lasts 7-14 days, but can occasionally be longer.

Preventing Kidney Infections

Kidney infections are generally caused by pre-existing UTIs. Therefore, the best way to thwart one is by preventing bacteria from entering the urethra or bladder in the first place. The following tips can help you be proactive about preventing potential infections:

  • Stay hydrated: Drink plenty of fluids (specifically water) daily. Drinking cranberry juice regularly can also help prevent infections.
  • Urinate regularly: Urinate when you feel the urge to go to the bathroom, especially after sexual intercourse.
  • Maintain good hygiene: After any bowel movement (and urinating, if you’re a woman) wipe the anus (and vagina) from front to back. This reduces the risk of spreading bacteria to the urethra, from where it can spread to your bladder and kidneys.

When to See a Doctor

With kidney infections, the key is prompt medical treatment, especially since they can develop quickly. So, go see your doctor at the first sign of any of the above-mentioned symptoms, or if they haven’t improved after a few days. A doctor’s visit is especially important if you’re experiencing any combination of the following:

The earlier you start antibiotics, the more likely your treatment may prevent complications or even hospitalization.

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K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Zina Semenovskaya, MD

Dr. Semenovskaya specializes in emergency medicine, and received her medical degree from Weill Cornell Medical College. She is currently the medical director at Remote Emergency Medicine Consulting, LLC and splits her time working clinically as an emergency medicine attending in California and Alaska. She is the first of our doctors to be fluent in Russian.