Blood Culture Test

What is a blood culture?

A blood culture is a lab test used to check for infection in the blood. These infections are most often caused by bacteria or fungi.

Some children are at higher risk for serious infections. If your child develops a fever or other signs of infection, it may indicate a serious illness. Health care providers need to quickly identify the cause so treatment can begin as soon as possible.

A blood culture is often done to help find the cause of the infection and plan treatment.

Blood infections in children with weak immune systems

If your child has cancer or another condition that weakens the immune system, their body may have a harder time fighting infection. Bloodstream infections can become serious quickly and often need treatment in a hospital. Sepsis is a serious condition that can happen in response to an infection. It is more common in children with weakened immune systems. 

Your child may need a blood culture if they have a fever or other signs of infection, especially if they have a weakened immune system or a medical device such as a central line. 

How a blood culture works

A care team member will collect blood in small vials or tubes. The amount of blood collected depends on your child’s age and weight. 

Blood culture samples are collected as soon as possible after a fever begins and before antibiotics are given. Usually, at least 2 sets of samples are collected with multiple bottles in each set. This helps identify the cause of the infection. 

Blood may be collected from: 

• A needle inserted into a vein   
• A central line, such as a port, a tunneled central line, or peripherally inserted central catheter (PICC line)

Each blood sample is placed into 1 or more bottles. These bottles contain substances that allow bacteria or fungi to grow. The samples are sent to a lab, where they are monitored for several days to see if germs grow. 

Blood culture results

If germs grow in the culture, the test is positive and indicates an infection. If no germs grow in the culture, the test is negative. 

A health care provider will use information about your child’s symptoms and the results of the blood culture to make a diagnosis. 

The lab may also do tests to see which medicine will work best against the germs. This test can take a few days or even longer. 

Your care team will share the results with you. They will work with you to create a treatment plan if there is an infection. 

Possible risks of a blood culture

A blood culture test is generally safe. Possible risks include: 

• Pain or discomfort at the needle site 
• Bleeding or bruising 
• Dizziness or feeling faint 
• Infection at the blood draw site (rare) 

Questions to ask your care team

• Why does my child need a blood culture? 
• What infections can a blood culture detect? 
• How will the blood sample be collected? 
• How long will it take to get the blood culture results? 
• What does it mean if the 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? 
• Will more tests be needed? 
• When should I call the care team or seek emergency care? 

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