A blood culture is a test to find an infection in the blood. The blood does not normally have any bacteria or fungi in it. A blood culture can show what bacteria or fungi are in the blood.
A bacterial infection in the blood, called bacteremia, can be serious because the blood can spread the bacteria to any part of the body. A blood infection most often occurs with other serious infections, such as those affecting the lungs, kidneys, bowel, gallbladder, or heart valves.
A blood infection may also develop when the immune system is weak. This can occur in infants and older adults, and from disease (such as cancer or AIDS) or from medicines (such as corticosteroids or chemotherapy) that change how well your body can fight infections (immunity).
To test for an infection in the blood, a sample of blood is collected and placed in a cup with special substances that allow the bacteria or fungus to grow. The type of bacteria or fungus that grows is checked with chemical tests and by looking at the culture under a microscope. Two or three blood samples from different veins are often taken to make sure a bacteria or fungus is not missed. If no bacteria or fungus grows, the blood culture is called negative. A blood culture is often done when a person has a fever because this is the time when the bacteria or fungus is most likely to have spread to the blood.
Why It Is Done
A blood culture is done to:
How To Prepare
You do not need to do anything before having this test. Tell your health professional if you have recently taken antibiotics.
How It Is Done
The health professional drawing blood will:
Blood is often collected from two or three different body sites. Or it may be collected at two different times a few hours apart.
Some people may have long-term catheters placed in a major vein because they are receiving chemotherapy or nutrition supplements for weeks or months at a time. For these people, blood for a blood culture will be collected from their catheters for this test.
How It Feels
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of a problem from having a blood sample taken from a vein.
A blood culture is a test to find an infection in the blood. Most bacteria can be seen in the culture in 2 to 3 days, but some types can take 10 days or longer to show up. Fungus can take up to 30 days to show up in the culture.
If bacteria are found in the culture, another test is often done to find the best antibiotic that will kill the bacteria. This is called sensitivity or susceptibility testing. Sensitivity testing is important so the blood infection is treated correctly. This also helps prevent bacteria from becoming resistant to antibiotics.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
What To Think About
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