Blood culture is the most widely used diagnostic tool for the detection of bacteremia and fungemia. It is the most important way to diagnose the etiol

What Causes False Positives? Understanding Blood Culture Contamination

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2021-07-23 21:30:08

Blood culture is the most widely used diagnostic tool for the detection of bacteremia and fungemia. It is the most important way to diagnose the etiology of bloodstream infections and has major implications for the treatment of those patients. However, blood cultures are frequently contaminated, which can lead to a “false positive” result. This can lead to substantial costs for the laboratory as well as negative outcomes among patients for whom blood cultures have been drawn.1

Blood culture contamination is defined as the presence of microorganisms in the blood culture bottle that entered during sampling but was not actually circulating in the patient’s bloodstream. Healthcare institutions in the United States are held to a performance standard of less than 3% contamination rates for blood culture,2 but numerous studies have shown contamination rates to be far higher than the 3% standard, with some studies showing as high as, “one-half of all positive blood cultures were judged by infectious disease physicians to represent contamination.”1 There are many possible sources of blood culture contamination, with some frequent sources including:1

The impact of blood culture contamination is felt in the microbiology laboratory and beyond. Contamination can have negative impacts on the lab, hospital system, and patients, with far-ranging consequences such as:1

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