Tests to Diagnose Infection

When a health care provider suspects an infection, they need to know:

• The cause of the infection
• Where the infection is in the body
• The severity of the infection

This information helps the provider choose the best plan of treatment. In some cases, your health care provider might start a treatment that targets a wide range of germs right away, even before they know exactly what's causing the infection.

Medical history and physical exam

Your health care provider will take a detailed medical history and perform a physical exam. They will look for signs and symptoms of illness and infection. These may include:

• Fever and chills
• Sore throat
• Body aches
• Respiratory signs and symptoms, such as a runny nose, cough, or shortness of breath
• Fast heartrate
• Diarrhea
• Vomiting
• Skin sores or ulcers
• Pain in the pelvis or abdomen (belly)
• Face or sinus pain
• Eye redness or swelling
• Urine (pee) that is bloody, cloudy, or smells bad; pain when urinating

After the physical exam, your health care provider may order tests to find out what kind of infection it is and how it has affected your child’s body.

Find out more about fever and signs of infection.

Cultures and lab tests

Blood cultures

A blood culture is a test to look for bacteria, fungi, or other germs in the blood. It involves drawing blood from your child and sending the blood sample to the lab.

Urinary infection tests

Your care team may collect a urine (pee) sample from your child for testing. A urine culture and urinalysis can detect germs or substances that indicate an infection or other health problem.

Respiratory infection tests

If your child has respiratory symptoms, such as a cough or a runny nose, a care team member may perform a nasopharyngeal swab. For this test, a sterile swab is inserted into your child’s nostril, along the floor of the nose, and into the space behind the throat (nasopharynx). The swab is rotated to collect a sample of cells and fluid and then removed.

Skin infection tests

If your health care provider sees signs of skin infection, they may do a skin biopsy to find the cause of infection. For the procedure, a care team member will numb the area and remove a piece of skin tissue to be examined in the lab. Your care team will explain how to care for the wound.

Wound infection tests

A wound culture may be done if a wound shows signs of infection. For the test, your care team will collect a sample of fluid or tissue from the wound. The sample is sent to a lab for testing.

Gastrointestinal infection tests

Your care team may collect a stool specimen for culture or other types of tests. A fresh stool sample must be collected in a clean container. It is important that the sample is not contaminated with other substances such as urine or water or by touching a toilet or diaper. A stool sample may also be collected with a swab of the rectum. Once the sample has been collected, it will be sent to a lab.

Central nervous system (CNS) infection tests

If your health care provider suspects a CNS infection, they may order a lumbar puncture test or an imaging study such as a brain MRI.

Getting test results and making a treatment plan

How long it takes to get test results depends on the type of test. Some test results might be ready within a few hours. Other results might take several days or longer.

If a germ is detected in any of your child’s labs or tests, your health care provider may order a susceptibility test. This test will show if the germ could be killed by antibiotics or if it will resist them. This test helps the provider select the best treatment.

Your health care provider will let you know when the results are available and discuss treatment options.

Sometimes, all test results may come back negative for infection. This means that the lab could not identify the type of germ causing the symptoms. If an infection is still suspected, your health care provider may decide to start or continue a treatment plan that works against most possible causes of the infection.

Questions to ask the care team

• What tests does my child need?
• How long will it take to get the results?
• What does it mean if the lab test or culture is positive?
• What will the next steps be if the test shows an infection?
• Will my child need treatment while we wait for the results?

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