Blood Culture

Test Overview

Blood normally doesn't 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. That's 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. It can happen because of a 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 found 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 that a bacteria or fungus is not missed.

Why It Is Done

A blood culture is done to:

How To Prepare

• In general, there's nothing you have to do before this test, unless your doctor tells you to.
• Tell your health professional if you took antibiotics recently.

How It Is Done

A health professional uses a needle to take a blood sample, usually from the arm.

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.

Watch

How It Feels

When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.

Risks

There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.

Results

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.