A patient has a markedly elevated WBC count. What could cause a false positive blood culture?

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Multiple Choice

A patient has a markedly elevated WBC count. What could cause a false positive blood culture?

The main idea is that false-positive blood cultures are most often due to contamination during collection rather than something the patient’s own cells would cause. When skin flora from the draw—bacteria that normally live on the skin—accidentally get into the culture bottle, they can multiply in the growth media and signal a positive result even though the patient doesn’t have true bacteremia. Having a markedly elevated white blood cell count shows the body's response to infection, but white blood cells are not pathogens and their metabolic activities don’t reliably create a positive culture signal. The idea that CO2 released by WBCs would provoke a false positive isn’t supported by how culture systems detect growth. Sample degradation tends to lead to false negatives by destroying organisms or their DNA, and rapid transport helps preserve the specimen rather than create a false positive.

The main idea is that false-positive blood cultures are most often due to contamination during collection rather than something the patient’s own cells would cause. When skin flora from the draw—bacteria that normally live on the skin—accidentally get into the culture bottle, they can multiply in the growth media and signal a positive result even though the patient doesn’t have true bacteremia.

Having a markedly elevated white blood cell count shows the body's response to infection, but white blood cells are not pathogens and their metabolic activities don’t reliably create a positive culture signal. The idea that CO2 released by WBCs would provoke a false positive isn’t supported by how culture systems detect growth. Sample degradation tends to lead to false negatives by destroying organisms or their DNA, and rapid transport helps preserve the specimen rather than create a false positive.

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