Blood Cultures (Bacteriology)
Bloodstream Infection, Sepsis, Neonatal Sepsis, Infective
endocarditis, Prosthetic valve endocarditis (PVE), Bacteraemia
The Blood Culture system can also be used for small volumes of
sterile fluid to aid the recovery of fastidious organisms, for
example but not limited to Vitreous aspirates, Joint Fluids
(Prosthetic and Natural), Cardiac pacemaker site aspirates, Stem
Cell fluids. The FAN (green top) bottle contains a charcoal
neutralising agent and is suitable for PD fluids.
Collection container (including
preservatives): Collect specimens in BactAlert
bottle. Use aseptic technique.
Specimen type: Venous blood, arterial blood,
peripheral blood, sterile fluids
Collection: A blood culture set is defined as
one aerobic (blue top) and one anaerobic (purple top) bottle. For
infants and neonates, a single aerobic (yellow top) bottle may be
requested. Small volume sterile fluids such as Pacemaker fluids and
stem cells can use single aerobic bottle (Yellow top).
Take two consecutive sets from two separate venepuncture sites
during any 24hr period for each septic episode. For neonates, take
a single aerobic bottle or special low volume bottle.
Take two sets during the first hour in cases of severe sepsis
prior to commencing antibiotic treatment, provided this does not
significantly delay antibiotic administration.
Take at least three sets during a 24hr period where the patient
has suspected infective endocarditis.
If patient is on antibiotics, or fungaemia is suspected use a
FAN (green top bottle) and anaerobic (purple top) bottle.
Specimen transport (eg at room temperature, or within 4
hrs): Collect specimens before antimicrobial therapy where
possible. Samples should be taken as soon as possible after a spike
of fever. Samples should not be refrigerated.
Inoculated bottles should be incubated as soon as possible, and
within a maximum of four hours. The four hour turnaround time from
collection to incubation for blood culture samples reflects their
Type and volume of sample:
Adults - Purple top and Blue top bottles. Inoculate up to 10mL
to each bottle.
Children - Yellow top bottle. Inoculate up to 4mL
Neonates - Yellow top bottle. Inoculate preferably 1-2mL.
Do not exceed the manufacturer's recommended maximum volume for
each bottle as shown on label.
- Use aseptic technique
- Inspect the blood culture bottles for damage
- Ensure that the blood culture bottles have not exceeded their
- Do not re-sheathe needles
Measurement units: Growth
detected or not detected
Biological reference units: Not applicable
Turn round time for provisional result (working
days): 24 hrs
Turn round time to final result (working days):
Clinical decision points: Not
Factors known to significantly affect the
results: Any recent antimicrobial therapy can have a
significant effect on blood culture results by decreasing the
sensitivity of the test. This may be of particular importance in
those patients receiving prophylactic antibiotics and who are at
high risk of bloodstream infections. If patients have received
previous antimicrobial treatment, bacteraemia should be considered
even if blood culture results are negative. There is a direct
relationship between blood volume and yield, with approximately a
3% increase in yield per mL of blood cultured. False negatives may
occur if inadequate blood culture volumes are submitted.
It is estimated that 2-5% of positives samples
may be missed if bottles are pre-incubated, these organisms may
fail to trip the threshold algorithm of the continuous monitoring
blood culture machine. This may occur with Abiotrophia species
(nutritionally variant streptococci), S. pneumoniae which have
undergone a degree of autolysis, and fastidious organisms which are
unable to grow on routine solid culture media.
Organisms may include:
- Campylobacter species
- Helicobacter species
- Capnophilic organisms
- Slow-growing anaerobes