Blood cultures

Blood culture tests are used to test for the presence of bacteria and yeast in the blood. Some forms of yeast and many different forms of bacteria (as well as viruses and fungi) are responsible for causing illness and infection.

Why is the test used?

The blood culture test is used to identify bacteria and yeast in the bloodstream; this is usually done to identify the source of an illness or infection and to help doctors to diagnose systemic infections (when the infection cannot be controlled at the site, the bacteria leak into the blood supply and this may cause other organs and parts of the body to become infected).

The test will usually be ordered when the patient shows signs or symptoms of sepsis (this is an inflammatory condition, which is caused by the body’s response to a systemic infection); symptoms include fatigue, chills, fever and a higher white blood count than usual.

How is the test performed?

The test is done by using a sample of blood taken from a vein in the arm; two samples will be taken and placed in different vials. The vials will contain nutrients that allow the bacteria or yeast to thrive; one will be oxygen-rich and the other will be anaerobic (without oxygen). The tests are usually carried out at intervals during a set period of time; this allows doctors to see microorganisms which are released into the bloodstream gradually and intermittently. Most laboratories monitor samples over a period of time.

The blood samples are usually collected from different veins in the arm.

What do the test results show?

If the test result comes back positive, this usually means the individual has an infection, which has been caused by a bacterium or a form of yeast. Sepsis is a serious, potentially life-threatening disease and will be treated very quickly in the event of a positive result.

If the tests come back negative, it is unlikely that the patient has sepsis; however, it may still be possible and if symptoms persist, the doctor may order further tests. The blood culture test may be carried out in addition to full blood count or urine, CSF (cerebrospinal fluid: this is the fluid which surrounds the spinal cord and the brain) or sputum tests.

Specific Blood Tests

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