A blood culture is a test used to detect organisms in the blood that cause infection. Blood infections occur when these organisms have spread from infected areas of the body into the blood.

Who is a candidate for the test?

Blood cultures are performed whenever a healthcare provider suspects that a person's symptoms are due to an infection in the blood.

How is the test performed?

In order to do a blood culture, a sample of blood is required. This sample of blood is usually obtained through a vein in the hand or arm. A thin piece of rubber is wrapped tightly around the arm, causing the vein to swell with more blood. The skin over the vein is carefully cleaned to remove the bacteria that are normally present on the skin.

A small needle is then inserted through the skin and into the vein. Once the needle is in the vein, blood is allowed to flow through the needle and into a test tube. The blood sample is then sent to the lab so cultures can be done.

A culture is an attempt to get organisms that may be present in the blood to grow and multiply. To do this, the blood sample is placed in specially prepared containers and warmed at different temperatures. When enough organisms grow and multiply, they can be identified. This process usually takes 1 to 3 days. In some cases, a culture may take weeks to develop. The organism identified may be a virus, bacteria, fungus, or another type of organism.

The healthcare provider will use blood culture results to select the appropriate medicine. Often, treatment is started before the culture results are known. The provider may need to switch medicines once the culture results come back.