Specimen collection details

  • Blood culture collection: Reducing our contamination rate

    Background

    Skin flora, such as coagulase negative staphylococci (CoNS), are a potential cause of infection in certain neonatal and paediatric patients, but they are also common contaminants in blood cultures.  This can lead to unnecessary investigations, treatment and costs for the patient.  It has been previously estimated that up to 50% of CoNS in blood cultures are related to contamination.  In addition, changes to surveillance definitions means that CoNS are no longer included in the monitoring of central line infections, unless the same organism is grown from two or more collections.  We would therefore like to reduce our contamination rate as much as possible by optimizing collection practices.

    What sort of blood culture do I need to take?

    • All patients should have an aerobic culture (in either a yellow or green bottle depending on blood volume)
    • Some patients also require an anaerobic culture:
    1. Oncology patients
    2. Suspected gastrointestinal, gynaecological or oral focus of infection and GI surgical patients
    3. Short gut syndrome patients
    • Other specialised culture bottles are available from the microbiology laboratory ext 5688 on request

    What colour bottle do I need?

    Bottles

    Bottle top colour

    Culture type

    Blood volume

    Yellow

    Aerobic Paediatric

    0.5-4mL

    Green

    Aerobic Adult

    5-10mL

    Orange

    Anaerobic

    5-10mL

    Black

    Mycobacterial

    5-10mL

    Silver

    Mycoplasma

    3-5mL

    How can I maintain asepsis?

    • Use a sterile basic dressing pack for your equipment
    • Blood cultures should be taken using sterile gloves after hand hygiene with microshield gel
    • Disinfect skin with Chlorhexidine 0.5% in 70% alcohol
      (in neonates use 1 % aqueous chlorhexidine)
    • Apply skin antiseptic in circular motion outwards from insertion site; allow to dry and repeat application

    What collection methods are acceptable?

    • Syringe and needle
    • Aspiration from hub of newly inserted cannula
    • Butterfly needle and syringe
    • Umbilical and central lines immediately after insertion
      DO NOT take blood from old peripheral intravenous cannulas

    How can I prevent contamination of my blood culture?

    • Use sterile gloves and avoid palpating vein after skin antisepsis
    • Swab blood culture bottle top after removing dust cap with alcohol swab and wait 30 seconds to dry
    • Innoculate blood culture bottle PRIOR to other blood tubes

    What cultures should I take if I suspect line sepsis?

    • A culture from the central line AND
    • A peripheral blood culture

    How many blood cultures should I take before starting antibiotics?

    • 2 cultures are optimal
    • This is particularly important in patients with central venous access
    • In a septic patient, antibiotics should not be withheld pending subsequent cultures

    How may blood cultures should I take in a febrile patient?

    • 3 blood cultures have been shown to have 96% sensitivity in detecting bacteremia
    • No more than 4 blood cultures should be necessary

    Prepared 12/5/2009 by Vanessa Clifford, Microbiology Registrar (pg 5735)