culture collection. Arterial blood samples do not increase
diagnostic yield, and blood specimens obtained from intravascular
lines have demonstrated increased rates of contamination
in some studies [10]. The American College of Physicians
guidelines recommend that collecting blood for culture from
intravascular devices be avoided, and the CLSI recommends
that, if one must collect a blood culture from an intravenous
line, it should be paired with a culture that is obtained via
venipuncture to assist in the interpretation of positive results
[11,12]. The timing of blood culture collection does not appear
to significantly affect the recovery of clinically relevant
microorganisms, and most authorities therefore recommend
collecting multiple sets simultaneously or over a short period
of time, except when documentation of continuous bacteraemia
is required for patients with endovascular infection
[12,13]. Whenever possible, two to four sets of blood
specimens should be collected from independent venipuncture
sites, and, for adult patients, each set should consist of 20–
40 mL of blood [12–15]. The volume of blood drawn from
infants and children is less well prescribed, but should be based
on the child’s age and not exceed 1% of the patient’s total
blood volume [12,16]. It is clear that the total volume of blood
cultured from adult patients is directly proportional to the
yield of microorganisms recovered. This is a consequence of
the fact that most adult patients with BSIs have very low
circulating concentrations of viable microorganisms. Inadequate
blood volume or the collection of a single blood culture
set significantly reduces the sensitivity of the test, and also
makes the interpretation of results far more difficult
[13,15,17,18]. Collection of multiple sets of blood cultures
from a single venipuncture or intravascular line should also be
avoided. For optimal recovery of diverse BSI aetiological
agents, each set of blood cultures should include paired
aerobic and anaerobic blood culture bottles, and the aerobic
bottle should be filled first [12,19,20].
Proper skin antisepsis prior to collection of blood cultures via
peripheral venipuncture is paramount, to reduce blood culture
contamination rates and facilitate result interpretation for the
clinician. A variety of skin disinfectants have been clinically
evaluated, and reports comparing their relative efficacy have
been published [21–25]. On the basis of these data, current
guidance documents conclude that tincture of iodine, chlorine
peroxide and chlorhexidine gluconate are superior to povidineiodine
preparations, and that tincture of iodine and chlorhexidine
gluconate are probably equivalent for skin antisepsis prior
to blood culture collection [12]. Although chlorhexidine
gluconate is an adequate disinfectant for older infants, children,
and adults, it should not be used on infants <2 months of age,
and an alternative is therefore required in centres where this
disinfectant is otherwise routinely employed.
Once optimal blood culture specimens are collected
according to the principles outlined above, they should be
sent to the laboratory as promptly as possible. These
specimens should never be refrigerated or frozen, and should
be held at room temperature for no more than a few hours if
necessary. Although an extended delay between blood culture
collection and incubation in a continuous-monitoring blood
culture instrument is not recommended, a significant diminution
in pathogen recovery has only been experimentally
observed when blood culture bottles have been held for
>24 h at 4°C or room temperature and for >12 h at 37°C
[26]. Lengthy incubation of blood culture bottles prior to
entering them into a continuous-monitoring blood culture
instrument may delay or impede the detection of growth by
the instrument, and is discouraged.
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