From the Guidelines
Two blood culture samples are typically drawn, but not always, with the standard practice being to collect two to three sets of blood cultures from different venipuncture sites when evaluating for bloodstream infections. This approach increases the diagnostic yield and helps distinguish true pathogens from contaminants. Each set usually consists of one aerobic and one anaerobic bottle. However, there are exceptions to this practice. In some situations, such as in pediatric patients with limited venous access, critically ill patients requiring immediate antimicrobial therapy, or when obtaining multiple samples is logistically difficult, a single blood culture may be collected. Additionally, for continuous bacteremia conditions like endocarditis, the timing between samples is less critical as the bacteria are constantly present in the bloodstream. The decision on the number of blood cultures should be based on clinical context, suspected diagnosis, and institutional protocols, balancing the need for diagnostic accuracy with practical considerations 1.
Some key points to consider when deciding on the number of blood cultures to draw include:
- The potential for contamination, which can be minimized by using proper skin preparation and sterile technique 1
- The need for rapid diagnosis and treatment, which may necessitate drawing multiple cultures simultaneously 1
- The presence of an intravascular catheter, which may require drawing cultures through the catheter as well as peripherally 1
- The clinical suspicion of a specific infection, such as endocarditis, which may require a different approach to blood culture collection 1
It's also important to note that the timing of blood culture collection can impact the results, with some studies suggesting that drawing cultures at the same time from different sites can be as effective as drawing them sequentially 1. Ultimately, the decision on the number of blood cultures to draw should be made on a case-by-case basis, taking into account the individual patient's needs and circumstances.
In terms of specific guidelines, the Surviving Sepsis Campaign recommends obtaining at least two sets of blood cultures (both aerobic and anaerobic bottles) before antimicrobial therapy, with at least one drawn percutaneously and one drawn through each vascular access device, unless the device was recently inserted 1. The Infectious Diseases Society of America also recommends obtaining two to three sets of blood cultures from different venipuncture sites when evaluating for bloodstream infections 1.
Overall, while two blood culture samples are typically drawn, the specific approach to blood culture collection should be tailored to the individual patient's needs and circumstances, taking into account the potential benefits and limitations of different approaches.
From the Research
Blood Culture Samples
- The number of blood culture samples drawn can vary, but two samples are commonly taken to increase the chances of detecting bacteremia 2.
- A study found that two or three blood culture sets almost always suffice to establish or rule out bacteremia, although on some occasions obtaining more than three sets of cultures is indicated 2.
- Another study showed that taking two blood cultures from different sites can improve the rate of pathogen detection compared to a single blood culture 3.
Benefits of Multiple Blood Culture Samples
- Multiple blood culture samples can help increase the sensitivity of detection and reduce the risk of overlooking bacteremia 4, 3.
- A study found that adding a second blood culture increased the culture yield by 7.6% and improved the detection of pathogens 3.
- Another study showed that more pathogenic microorganisms were recovered from paired aerobic and anaerobic bottle sets compared to single bottles 5.
Clinical Importance of Blood Culture Results
- The clinical importance of increased sensitivity of blood culture bottles has been demonstrated, with a study finding that the majority of additional episodes detected were clinically important 6.
- Blood culture results can inform treatment decisions and improve patient outcomes, highlighting the importance of accurate and timely detection of bacteremia 4, 6.