3.2 The principles of sample collection

Collecting the sample requires great attention to detail. Education and training should be available to clinicians to ensure that they collect samples that will provide useful and accurate laboratory results.

It is critical to avoid contamination with normal microbial flora from the patient, and from the person taking the sample: otherwise, treatment might be misdirected. Avoiding contamination is particularly important for cultures of blood, bone and other tissues or fluids in which infection is often caused by indigenous flora, and for specimens collected from sites of putative infection that are contiguous to or adjacent to cutaneous or mucosal surfaces. It is therefore necessary to use strict aseptic technique from anatomic sites most likely to yield pathogenic microorganisms.

Activity 3: Collecting blood culture samples

Timing: Allow 30 minutes

Watch the video ‘Prof Koch’s guide to perfect blood cultures’ [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] , which discusses the collection of samples for blood culture. Then complete the two tasks below.

  1. Make a note of the details of appropriate blood culture collection procedure mentioned in the video.
  2. How do you think your hospital could ensure blood culture samples are taken correctly?
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Discussion

  1. You may have noted the following requirements:
    • When testing for bacteraemia, try to take a sample as the temperature begins to spike
    • Take the blood culture sample before administering antimicrobials
    • Avoid the femoral vein
    • Avoid existing cannulae and lines
    • Bottles must be in date and in good condition
    • Disinfect site with 2% chlorhexidine with 70% isopropyl alcohol
    • Allow the site to dry thoroughly after disinfection
    • Don’t touch the skin again after disinfection
    • Swab the rubber tops of the bottles with ethanol, and allow to dry
    • Inoculate aerobic bottles before anaerobic bottles
    • Collect as much blood as possible
    • Discard the needle directly into the sharps box to avoid needle stick
    • The bottle must be correctly labelled
    • Keep bottles at room temperature
  • Note that there are alternatives for disinfection, such as 10% povidone-iodine (see Table 2).
  1. You may have noted the following:
    • The laboratory could provide a checklist for samples and refuse to test samples submitted without full details or otherwise incorrectly managed.
    • Posters could be put up in wards showing the agreed correct procedure, using diagrams.
    • Regular refresher training could be provided to healthcare staff taking blood culture samples.
  • Note that there are different options for the procedure, so details of these can be agreed by discussion between the clinical and laboratory sectors.

3.1 What affects appropriate sample selection?

3.3 Handling and transporting specimens correctly