What’s a blood culture?

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Blood cultures can detect bacteria or infectious agents in the bloodstream, often used when a blood infection is suspected or when infection is difficult to scan. The procedure involves at least two blood draws, and samples are monitored for up to five days to determine the presence of bacteria. Newborns, the elderly, and those with weaker immune systems are more susceptible to bloodstream infections.

A blood culture is part of a blood test that can help determine if a person has bacteria or other infectious agents in their bloodstream. Blood cultures may be needed when a blood infection such as septicemia is suspected or when infection is thought to exist in areas that are difficult to scan. For example, if people have bacterial endocarditis and the bacterial matter doesn’t show up on X-rays or echocardiograms, doctors might use a blood culture to determine its presence, because some bacteria spread into the bloodstream from the heart.

For people who have a blood culture, the procedure is fairly simple, but it does involve at least two blood draws, usually from different areas of the body, such as opposite arms. Each arm is swabbed with alcohol to prevent the skin from contaminating the blood sample with normal skin bacteria. The samples taken are then specially treated to see if any bacteria will grow.

This usually means placing the samples in a machine that keeps them at body temperature, so if bacteria are present, they will continue to grow. The samples are then monitored for up to five days to determine if bacteria exist. At the same time, or after a positive blood culture, meaning the presence of bacteria, doctors need to figure out what type of bacteria is present to determine the best way to treat it. They may use a process called subculture, in which they grow bacteria on special agar plates to determine their type.

The time it takes to determine if a blood culture is positive can vary. Samples can be stored for up to five days to make sure nothing appears to “grow” in the blood drawn. Usually, if the bacteria is present in the body and it has been caught in the sample, which is not always the case, it takes a couple of days before the blood culture can be determined to be positive. Sometimes negative blood cultures aren’t accurate, and people may need to run several tests over several days if doctors reasonably suspect a bacterial or fungal infection in the bloodstream.

There are people who are more likely to get a blood culture. Newborns and the elderly are more susceptible to bloodstream infections because they have weaker immune systems. Additionally, those with immunosuppressive illnesses such as lupus or AIDS may automatically be more suspected of having bloodstream infections if they experience symptoms such as high fever, chills and body aches. However, these symptoms aren’t always an indication of blood infection and could instead signal that someone has a bad virus like the flu virus. Also, anyone at any age can develop a blood infection.




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