What Is a Blood Culture Test?

A blood culture test helps your doctor figure out if you have a kind of infection that is in your bloodstream and can affect your entire body. Doctors call this a systemic infection. The test checks a sample of your blood for bacteria or yeast that might be causing the infection.

Why Would I Need One?

If your doctor orders this test, it’s because he thinks you might have a systemic infection and he wants to check for certain kinds of germs in your blood. It can help him come up with the best treatment for you.

Your doctor might order the test if you have symptoms that may include:

If your infection is more severe, you might have:

What Happens During the Test?

A nurse or a phlebotomist (a medical technician who takes blood) will clean your skin and insert a thin needle into your vein to draw your blood. The process will be repeated using another vein to get the most accurate results.

In a lab, your blood samples will get mixed with a special material called a culture. It helps bacteria or yeast grow if they are already in your blood.

You may be able to get early results within 24 hours of your blood tests. But you might need to wait 48 to 72 hours to learn what kind of yeast or bacteria is causing your infection. You might need other tests, too.

You may be able to get early results within 24 hours of your blood tests. But you might need to wait 48 to 72 hours to learn what kind of yeast or bacteria is causing your infection. You might need other tests, too.

What Do the Results Mean?

Your doctor may talk about “positive” and “negative” results. If you get a “positive” result on your blood culture test, it usually means there are bacteria or yeast in your blood. “Negative” means there’s no sign of them.

If two or more of your blood cultures come back positive for the same type of bacteria or fungi, it’s likely that that’s the type of bacteria or yeast that’s causing your infection. An infection in your blood is serious. You’ll need immediate treatment, probably in a hospital.

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What If My Results Are Positive and Negative?

If one of your blood culture tests comes back positive and the other comes back negative, it still could mean you have an infection. But it could also mean that one of the blood samples was contaminated with bacteria from your skin. Your doctor might order more tests or need more information before making a diagnosis.

If you get re-tested and both of your blood culture tests are negative, you probably don’t have a blood infection caused by bacteria or yeast. But if you continue to have symptoms, you might need more tests.

If My Results Are Negative, Why Do I Have Symptoms?

There are a few reasons. Some types of bacteria and yeast are hard to grow in a culture, so you might need to get a special kind of culture.

Also, these cultures can’t detect viruses. So if you have a viral infection, you may need other tests.

WebMD Medical Reference Reviewed by Melinda Ratini, DO, MS on December 14, 2016

Sources

SOURCES:

University of Rochester Medical Center: “Blood Culture.”

KidsHealth.org: “Blood Culture.”

Lab Tests Online: “Blood Culture: The Test.”

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