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. (1)
It’s important to see a healthcare provider right away if you experience symptoms of a kidney infection, which include painful or frequent urination, cloudy or smelly urine, fever and chills, pain in your lower back or side, and nausea and vomiting. If it isn’t diagnosed and treated promptly, a kidney infection can cause both immediate and long-term severe complications.
To diagnose a potential kidney infection, your doctor will ask you about your symptoms. You’ll also most likely be asked about your history of health conditions, to determine whether you’re at increased risk for a kidney infection.
Your doctor will also perform a physical exam to see if you have any redness or tenderness on your torso that’s consistent with a kidney infection.
If your doctor suspects a kidney infection at this point, you’ll be asked to give a urine sample for lab tests to look for a bacterial infection.
You may also undergo imaging tests, which can look for enlargement or other abnormalities in your kidneys that indicate an infection. (1,2)
Medical History and Physical Exam
At your doctor’s appointment, you’ll be asked about the symptoms you’ve been experiencing recently: what they are, how they’ve changed, and how long you’ve noticed them.
You’ll also be asked about your history of health conditions, such as:
- A UTI within the last year
- Pregnancy (current or recent)
- Any known problems in your urinary tract
- Kidney stones
- Enlarged prostate
- Vesicoureteral reflux (VUR), in which urine flows backward into your kidneys
- Diabetes
- Any condition that may compromise your immune system, such as HIV or taking drugs for an organ transplant or autoimmune disease
- Spinal cord injury
- Nerve damage in your abdomen
- Urinary retention, or trouble emptying your bladder
- Use of a catheter to help empty your bladder (2,3)
During your physical exam, you’ll have your temperature, blood pressure, and heart rate taken. A fever, elevated heart rate, and low blood pressure can all be signs of an infection. (4)
Your doctor will examine your abdomen and back for signs of redness, swelling, or tenderness. He or she will check for tenderness in an area called the costovertebral angle (CVA) by gently tapping the area of your back that your kidneys are located underneath.
This maneuver disturbs any inflamed tissue around your kidneys, causing pain if you have a kidney infection.
If you’re a woman, your doctor may perform a pelvic exam to look for signs of inflammation or tenderness associated with a UTI. (5)
If you’re a man, your doctor may perform a digital rectal exam. In this procedure, you’ll be asked to expose your buttocks and bend over a table or lie on your side while holding your knees close to your chest.
Your doctor will insert a gloved, lubricated finger into your anus to feel for a swollen or enlarged prostate. (1)
Lab Tests for Kidney Infection
The most common lab tests to help diagnose a kidney infection are two types of urine test:
Urinalysis For this test, you’ll urinate into a container at your doctor’s office or lab. A sample of your urine will be viewed under a microscope, to look for bacteria or white blood cells, which can indicate an infection.
It’s possible for healthy people to have bacteria in their urine, so it’s important for urinalysis results to be viewed in the context of your symptoms, rather than as definitive evidence of an infection.
Urine Culture To help determine what kind of bacteria are causing your infection and guide your treatment, a sample of your urine may be placed in a container where the bacteria can grow. (1,2) Results from this test take two to three days to come back.
In some cases, your doctor may order a blood test to look for signs of an infection. This can involve two different tests:
Peripheral Blood Smear For this test, a thin layer of your blood is viewed under a microscope to look for an elevated white blood cell count and for neutrophils, the type of white blood cells that fight infection.
Blood Culture A sample of your blood is placed in a container to encourage bacterial growth, then examined over one to three days for bacteria that would indicate an infection. (4)
While 20 to 30 percent of kidney infections show positive blood culture results, there’s little evidence that this testing helps guide treatment or improve outcomes, according to Johns Hopkins Medicine. (5)
Imaging Tests for Kidney Infection
It’s usually unnecessary to order imaging tests to diagnose a kidney infection, according to the American Academy of Family Physicians. (4) Cases in which an imaging test may be helpful include:
- Your symptoms don’t improve with treatment
- Your infection recurs
- Your doctor suspects a structural abnormality in your urinary tract (4)
If your doctor believes that imaging tests are necessary, the following options are available:
Computerized Tomography (CT) Scan This test takes a series of X-ray images from different angles, which a computer combines to create detailed images of tissues in your body. (1,6)
Magnetic Resonance Imaging (MRI) This test uses a magnetic field and radio waves to create images of organs and tissues. (1,7)
Ultrasound This test uses sound waves to create images of tissues. But since sound doesn’t travel well through certain tissues, like bone, ultrasound has limitations. (1,8)
Intravenous Pyelogram This test involves injecting a dye into your arm, then taking X-ray images of your urinary tract to look for signs of swelling or other abnormalities in your kidneys and bladder. (9)
Voiding Cystourethrogram This test is similar to an intravenous pyelogram and involves taking X-ray images of your bladder when it’s full and while you’re urinating. (10)