Blood Cultures

What is a blood culture?

If you've been a patient in the hospital, you've probably had your blood drawn. Although it can be painful, it's done for an important reason.

Sometimes your blood is collected for a blood culture. The hospital lab tests your blood to look for microbes (germs) that may be causing infection. This information can help doctors prescribe the most effective medicine to get you better.

Why is a blood culture performed?

If you're hospitalized for pneumonia or a urinary tract infection, it can be difficult to choose the correct medicine to treat the infection. Most infections are caused by many different microbes, so it's important to figure out which of them is causing your infection.

A blood culture can be performed to determine whether the infectious agent is in your bloodstream. Symptoms of an infection in your bloodstream might include a high fever or chills. For a urinary tract infection, a urine culture might be helpful. In the case of pneumonia, your doctor may want a sputum culture.

The results of a blood culture can help doctors choose the correct medicine for your infection. For example, you may have a urinary tract infection. Your doctor prescribes medicine for it, but after three or four days, you're still not better. Could the medicine be targeting the wrong microbe? It's certainly possible. Your blood culture results can help indicate which microbe is the cause and your medicine can be changed. Blood culture results can give precise information about your infection.

Also, blood cultures that come back positive for back pain indicate a more severe type of infection, what is commonly referred to as blood poisoning, which is associated with complications like shock, respiratory failure and death. Blood cultures that come back positive alert your physician that your infection is serious and requires aggressive treatment with intravenous antibiotics.

How is a blood culture performed?

Your blood is collected in small bottles, which are sent to the lab. Tests are run to see if any microbes grow from your blood. If something grows, the lab runs more tests to detect the exact type of microbe.

How long does the test take?

It only takes a few minutes to collect blood, but it may take the lab several days to get any results.

What are the risks?

The risks of having blood drawn are minimal. You may get a bruise at the needle site. The chance of serious injury is very small. You should be aware, though, that results are not perfect - occasionally, a culture produces what's called a "false positive" or "false negative." If there is doubt, the doctor may want to repeat the test.

A blood culture can provide very important information when someone has an infection. So the next time you need to have blood culture drawn, remember that it could save your life.

Sources:

American Association for Clinical Chemistry

American Society for Clinical Pathology

National Institutes of Health (NIH)

This article was reviewed and updated June 2007.