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Home > Health Library > Blood Culture
The blood does not normally have any bacteria or fungi in it. A blood culture is a test of a blood sample to find germs (such as bacteria or a fungus) that can cause an infection.
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).
For a blood culture, a sample of blood is added to a substance that promotes the growth of germs. The type of germ may be identified using a microscope or chemical tests. Sometimes other tests are done to find the right medicine for treating the infection. This is called sensitivity testing. Two or three blood samples from different veins are often taken to make sure a bacteria or fungus is not missed.
A blood culture is done to:
You do not need to do anything before having this test. Tell your health professional if you have recently taken antibiotics.
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.
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.
No bacteria or fungus is found. Normal culture results are called negative.
Bacteria or fungus grows in the culture. Abnormal culture results are called positive.
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.
Reasons you may not be able to have the test or why the results may not be helpful include:
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
Current as of: December 9, 2019
Author: Healthwise StaffMedical Review: E. Gregory Thompson, MD - Internal MedicineAdam Husney, MD - Family MedicineMartin J. Gabica, MD - Family Medicine
Current as of: December 9, 2019
Author: Healthwise Staff
Medical Review:E. Gregory Thompson, MD - Internal Medicine & Adam Husney, MD - Family Medicine & Martin J. Gabica, MD - Family Medicine
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