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Blood Culture

When childhood cancer patients develop a fever or certain other symptoms of infection, it could be a sign of a life-threatening illness. Health care providers need information about what is causing the symptoms, so the patient can be treated as quickly as possible.

A blood culture will likely be performed to help find the source of the infection.

The body develops a fever because its temperature increases as the body tries to defend itself against invasion of microorganisms such as bacteria, fungi, or viruses. The patient may have other symptoms such as chills, fatigue, and body aches.

A fever develops because the body’s temperature increases from the effort to defend itself against bacteria, fungi, or viruses.

A fever develops because the body’s temperature increases from the effort to defend itself against bacteria, fungi, or viruses.

Blood infections in childhood cancer patients are serious

Childhood cancer patients’ immune systems often cannot defend their bodies against infections well. Their immune systems may not work properly because infection-fighting white blood cells have been destroyed by chemotherapy and radiation. Patients with cancers of the blood and bone marrow (leukemia and lymphoma) may not make enough of these cells, or these cells may not work well.

Blood infections are serious and need to be treated immediately, usually in a hospital. Sepsis is a complication that can be life-threatening, especially in people with weakened immune systems.

Information from blood cultures may help the doctor decide how long to continue antibiotics and which antibiotics are most effective for the patient’s infection.

Blood cultures are usually performed any time a childhood cancer patient develops a fever.

How a blood culture is performed

A blood culture requires samples of blood.

  • Each blood sample goes into 1 or more bottles. Each one has different substances (called a culture medium) in it to allow various types of bacteria and fungi to grow.
  • Health care providers typically want at least 2 samples of blood because they are trying to determine the source of the infection.
  • A frequent source is the patient’s venous access device such as a central line, port, or peripherally inserted central catheter (PICC).
  • When patients with a fever have such a device, the care team usually needs to take at least 1 sample of blood from the device (or possibly more than 1 depending on the device’s design) and then at least 1 blood sample from another part of the body, typically an arm. This blood sample will require an intravenous (IV) stick.
  • The amount of blood needed depends on the patient’s age and weight.
  • The culture should be obtained as soon as possible after a fever is detected and before antibiotics are administered.
  • Before the blood sample is taken, all areas are cleaned thoroughly with an antiseptic solution so another source of bacteria/ fungi doesn’t contaminate the blood sample.
  • The person performing the tests (usually a nurse) will take precautions to prevent contaminating the sample.

Preparing patients for a blood culture

There are not any special preparations required for a blood culture. It will likely require a needle stick. Some children fear needles, so parents may need to comfort and/or distract their children during the procedure. Child life specialists can also help and support children.


The blood sample is sent to a pathology lab where it will undergo different techniques to enhance detection of any microorganisms that may be present. After 24-48 hours (or longer in some cases), laboratory technologists can examine the material under the microscope to detect and identify any bacteria and/or fungi that are present. Not all positive blood cultures mean blood infection. Despite efforts to prevent it, bacteria or fungi can still sometimes get into the bottle from the patient’s skin or venous access device. This is called blood culture contamination and can be confusing. Doctors can use information about the patient's clinical condition and the lab test results to try to tell the difference.

The laboratory staff may also perform testing to determine the most effective antimicrobial treatments. Results of these tests can take a few days or even longer to come back.

The patient’s physician will share testing results with the family and will work with them to develop a treatment plan if there is an infection.

Reviewed: August 2022