Kidney Infection Diagnosis
Urological HealthKidney Infection

How a Kidney Infection Is Diagnosed

How a Kidney Infection Is Diagnosed
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Updated on January 8, 2026
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A kidney infection (known as pyelonephritis) usually happens when a urinary tract infection (UTI) spreads from your bladder up through the tubes that connect the bladder to your kidneys. Less commonly, it can happen when a blood infection spreads to your kidneys.

It’s important to see a healthcare provider right away if you experience symptoms of a kidney infection. Symptoms include painful or frequent urination, cloudy or smelly urine, fever and chills, pain in your lower back or side, and nausea and vomiting. Without early treatment, a kidney infection can lead to complications.

medical graphic on How Kidney Infection Affects the Body, man centered surrounded by symptoms including confusion, abdominal pain, painful urination, cloudy or discolored urine, frequent urination, nausea or vomiting, lower back pain, pelvic pain, fever
A kidney infection can cause any of these symptoms.Everyday Health
To diagnose a potential kidney infection, your doctor will ask you about your symptoms and any existing health conditions.

 Your doctor will also perform a physical exam and may collect a urine sample or order imaging tests to make the diagnosis.

Medical History and Physical Exam

At your appointment, your doctor will ask about your symptoms, how they’ve changed, and how long you’ve noticed them.

Your doctor will also ask about your health history and whether you have any conditions that may increase your risk of a kidney infection, such as:

  • Kidney stones
  • Enlarged prostate
  • Pregnancy
  • Vesicoureteral reflux (VUR), a condition in which urine flows back up into your kidneys
  • Diabetes
  • Any condition that weakens your immune system, such as HIV

During your physical exam, your doctor will check for fever, elevated heart rate, and low blood pressure, which can be signs of an infection. Your doctor will also examine your lower back and sides for signs of pain or tenderness, which may indicate a kidney infection.

If you’re a man, your doctor may perform a digital rectal exam to check for a swollen or enlarged prostate. An enlarged prostate can lead to a urinary tract infection.

Lab Tests for Kidney Infection

Doctors commonly use two types of urine tests to help diagnose a kidney infection.

  • Urinalysis This test involves examining a sample of your urine under a microscope to look for bacteria or white blood cells. The presence of bacteria may indicate a kidney infection when accompanied by other symptoms.

  • Urine Culture A urine culture helps a doctor identify the type of bacteria that is causing an infection. This is done by placing a sample of your urine in a container where the bacteria can grow. Results typically take a few days.

In some cases, your doctor may also order blood tests to help diagnose an infection. These may include a blood culture to check for bacterial growth and tests to check for elevated white blood cells.

Imaging Tests for Kidney Infection

Your doctor may order imaging tests if your symptoms don't improve with treatment, are more serious, or they suspect another condition, like a kidney stone.

Imaging test to help diagnose a kidney infection include:

  • Computerized Tomography (CT) Scan This test uses X-ray images to create detailed images of tissues in your body.
  • Magnetic Resonance Imaging (MRI) This test uses a magnetic field and radio waves to create images of your organs and tissues.

  • Ultrasound This test uses sound waves to create images of your organs.
  • Voiding Cystourethrogram This involves injecting a contrast dye to take X-ray images of your bladder when it’s full and during urination.

The Takeaway

  • A kidney infection typically happens when a urinary tract infection (UTI) spreads to your kidneys. Symptoms can include fever, chills, painful urination, and lower back pain.
  • Diagnosing a kidney infection typically involves assessing your symptoms, reviewing your health history, and performing a physical exam. It may also involve urine or blood tests and imaging tests, like a CT, MRI, or ultrasound.
  • Prompt diagnosis and treatment for a kidney infection is important to prevent further complications.

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Igor Kagan, MD

Medical Reviewer
Castle Connolly Top Doctor

Igor Kagan, MD, is an an assistant clinical professor at UCLA. He spends the majority of his time seeing patients in various settings, such as outpatient clinics, inpatient rounds, and dialysis units. He is also the associate program director for the General Nephrology Fellowship and teaches medical students, residents, and fellows. His clinical interests include general nephrology, chronic kidney disease, dialysis (home and in-center), hypertension, and glomerulonephritis, among others. He is also interested in electronic medical record optimization and services as a physician informaticist.

A native of Los Angeles, he graduated cum laude from the University of California in Los Angeles (UCLA) with a bachelor's in business and economics, and was inducted into the Phi Beta Kappa honor society. He then went to the Keck School of Medicine at the University of Southern California (USC) for his medical school education. He stayed at USC for his training and completed his internship and internal medicine residency at the historic Los Angeles County and USC General Hospital. Following his internal medicine residency, Kagan went across town to UCLA's David Geffen School of Medicine for his fellowship in nephrology and training at the UCLA Ronald Reagan Medical Center. After his fellowship he stayed on as faculty at UCLA Health.

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Quinn Phillips

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A freelance health writer and editor based in Wisconsin, Quinn Phillips has a degree in government from Harvard University. He writes on a variety of topics, but is especially interested in the intersection of health and public policy. Phillips has written for various publications and websites, such as Diabetes Self-Management, Practical Diabetology, and Gluten-Free Living, among others.

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Resources
  1. Symptoms & Causes of Kidney Infection (Pyelonephritis). National Institute of Diabetes and Digestive and Kidney Diseases. October 2024.
  2. Diagnosis of Kidney Infection (Pyelonephritis). National Institute of Diabetes and Digestive and Kidney Diseases. October 2024.
  3. Kidney Infection (Pyelonephritis). Cleveland Clinic. January 31, 2023.
  4. Urinalysis. Mayo Clinic. October 24, 2023.
  5. Urine Culture: Definition. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
  6. Kidney Infection: Diagnosis and Treatment. Mayo Clinic. Aug. 06, 2022.
  7. Kidney infection (Pyelonephritis) symptoms, treatment and prevention. American Kidney Fund. October 8, 2025.
  8. MRI. Mayo Clinic. September 09, 2023.