Tests to Diagnose Infection

When a health care provider thinks your child may have an infection, they need to know: 

• What is causing the infection 
• Where the infection is in the body 
• How severe the infection is 

This information helps them choose the best treatment. In some cases, they may start treatment right away to target the most likely germs, even before the exact cause of infection is known. 

Contact your health care provider if your child has signs or symptoms of infection, especially if they have a weakened immune system. The earlier an infection is diagnosed, the easier it is to treat. 

Medical history and physical exam

Your health care provider will: 

• Review your child’s medical history 
• Complete a physical exam 
• Look for signs and symptoms of infection, such as: 
  • Fever and chills
  • Body aches 
  • Respiratory signs and symptoms, such as a runny nose, cough, or shortness of breath 
  • Fast heart rate 
  • Sore throat 
  • Face or sinus pain 
  • Eye redness or swelling 
  • Sores on the skin or mouth 
  • Pain in the pelvis or abdomen (belly) 
  • Diarrhea, nausea, or vomiting 
  • Urine (pee) that is bloody, cloudy, smells bad, or causes pain when peeing 

Readying a patient's arm for blood drawAfter the exam, your health care provider may order tests to see what kind of infection your child has and how it is affecting their body. 

Blood cultures

Blood cultures help detect bacteria or fungi in the blood. To collect a sample, a care team member draws blood from your child’s vein, IV, or central line (central venous catheter).

Urinary infection tests

A urine culture and urinalysis are used to check for bacteria or other signs of infection in the urine (pee). Your child will usually provide a urine sample by peeing into a sterile cup.  

Respiratory infection tests

A nasopharyngeal swab helps look for infection in the respiratory tract. For this test, a care team member gently inserts a soft swab into your child’s nostril to collect a sample from the back of the nose and throat (nasopharynx). 

Skin infection tests

Skin swabs and biopsies help identify a skin infection. To collect a sample, a care team member may gently rub a soft swab over the affected area. They may also numb the area and remove a small piece of skin tissue (a biopsy). 

Wound infection tests

A wound culture can help reveal an infection. For this test, a care team member will collect a sample of fluid or tissue from the wound. If germs grow from the sample, it may help confirm an infection.   

Gastrointestinal infection tests

Stool tests are used to detect an infection in the stool (poop). Your child will usually provide a stool sample by pooping into a sterile cup. In some cases, a care team member may collect a sample with a swab of the rectum. 

Central nervous system (CNS) infection tests

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

Getting test results and making a treatment plan

How long results take depends on the test. Some results are ready within a few hours. Others may take several days or longer. 

If a germ is detected, your health care provider may order a susceptibility test to see which medicines and treatments will work best to treat the infection. 

Sometimes, test results do not identify a specific germ. If infection is still suspected, your health care provider may start or continue a treatment that targets the most likely causes. 

Questions to ask the care team

• What tests does my child need to diagnose an infection? 
• How long will it take to get the results? 
• How should my child prepare for the test? 
• What does it mean if the lab test or culture is positive? 
• What happens if the test shows an infection? 
• How accurate is the test? Is it possible to get an inaccurate or false result? 
• Will my child need treatment while we wait for the results? 
• Will my child need repeat testing? 
• What signs and symptoms of infection should I watch for? 
• What happens if the cause of infection is not found? 

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