Overview & Description
A test called a blood cultureis done to see if there is an infection of the blood. There are different types of bloodculture tests. One of these tests checks for a type of organism called aerobic bacteria.
Bacteria are tiny organisms that can live in both the human body and ourenvironment. The aerobic type of bacteria can live and grow only where there is oxygen.
Some bacteria cause illness. Others pose no problems to humans or may behelpful. But even harmless bacteria can become harmful if certain conditions allow them to:
Who is a candidate for the test?
This test is done most often with very young or old people or with those who haveweakened immune systems. However, it may be used any time a person has a seriousinfection. This is because most severe infections can spread to the blood. Kidney andlung infections are two of the most common causes of blood infections.
Signs of a blood infection may include:
Other symptoms are often due to the underlying infection that has spread tothe blood. For example, a person with a lung infection may have acough.
How is the test performed?
Blood samples for this test are usually taken from veins in the forearm orthe back of the hand. The samples may be taken from two different sites. This increasesthe chance of detecting bacteria in the blood. This can also help to rule outcontamination of the test by bacteria from the skin or from another source. Two or moreblood samples may be collected from each site so aerobic and anaerobic bacteria canboth be detected. Anaerobic bacteria can live and grow without oxygen, and some mayeven die when exposed to oxygen.
First, a band is tied around the upper arm to slow the circulation. This enlarges the veins below.A puncture site is selected and cleaned. Next, a needle is inserted into a vein. Blood is collectedand placed into a vial. The vial contains special food that helps the bacteria to grow. Theneedle is removed from the person’s arm, and the vial is sent to the lab. A bandage isput on the puncture site to stop any bleeding.
In the lab, the vial is watched to see if bacteria grow. It takes from 24 to 72hours or longer for aerobic bacteria to grow. If bacteria grow, the lab can identify themusing special tests.
Preparation & Expectations
What is involved in preparation for the test?
No preparation is needed for this test.
Results and Values
What do the test results mean?
Normal blood does not contain bacteria. If any bacteria are found with thistest, the result is abnormal. This is called a positive test or a positive blood culture. Apositive test generally means one of two things:
If a person has a positive test from contamination, no treatment is needed. Ifa person has bacteria in his or her blood, antibiotic treatment is needed. This test allows thebacteria that are causing the infection to be identified and treated. For example, anantibiotic may kill one type of bacteria and be totally ineffective against another type ofbacteria.
Examples of aerobic bacteria that may cause blood infections include:
In some cases, a person may have a blood infection, but the test is stillnegative. Sometimes, bacteria are only in the blood from time to time, which may makethe test falsely negative. Repeated blood culture tests may be ordered if this type ofsituation is suspected.
Article type: xmedgeneral