Alonna Norberg, Norman C. Christopher, Maria L. Ramundo, John R. Bower, Shirley A. Berman. Contamination Rates of Blood Cultures Obtained by Dedicated Phlebotomy vs Intravenous Catheter. JAMA. 2003;289(6):726–729. doi:10.1001/jama.289.6.726
Author Affiliations: Divisions of Emergency Medicine (Drs Norberg, Christopher, Ramundo, and Ms Berman) and Infectious Diseases (Dr Bower), Department of Pediatrics, Children's Hospital Medical Center of Akron, Akron, Ohio; and Departments of Emergency Medicine and Pediatrics, Northeastern Ohio Universities College of Medicine, Rootstown (Drs Norberg, Christopher, Ramundo, and Bower).
Context Blood culture is the criterion standard for identifying children with
bacteremia. However, elevated false-positive rates are common and are associated
with substantial health care costs.
Objective To compare contamination rates in blood culture specimens obtained from
separate sites vs through newly inserted intravenous catheters.
Design, Setting, and Participants Observational study conducted January 1998 through December 1999 among
patients aged 18 years or younger who were seen at a US children's hospital
emergency department and had a blood culture obtained as part of their care.
Medical records were reviewed in all cases with a positive blood culture.
Patients with indwelling vascular catheters were excluded.
Intervention All phlebotomy was performed by emergency department registered nurses.
During the baseline phase, blood specimens for culture were obtained simultaneously
with intravenous catheter insertion. During the postintervention phase, specimens
were obtained by a separate, dedicated procedure.
Main Outcome Measure Contamination rate in the postintervention period compared with the
Results A total of 4108 blood cultures were evaluated, including 2108 during
the baseline phase and 2000 in the postintervention phase. The false-positive
blood culture rate decreased from 9.1% to 2.8% (P<.001).
A statistical process control chart demonstrated a steady-state process in
the baseline phase and the establishment of a significantly improved steady
state in the postintervention phase. Young age was associated with increased
contamination rate in both the baseline and postintervention periods.
Conclusion Blood culture contamination rates were lower when specimens were drawn
from a separate site compared with when they were drawn through a newly inserted
Fever is the primary complaint in up to 20% of children presenting to
emergency departments,1 and bacteremia is the
source of fever in 1.5% to 2.3% of these patients.2,3 Blood
culture is the criterion standard for identifying children with bacteremia4- 7; however,
false-positive blood cultures are common and may add significantly to health
care costs.8- 11 High
rates of contamination are common among pediatric patients, likely related
to difficulties inherent to phlebotomy in young patients.12 To
minimize the number of venipunctures in children, blood culture specimens
are obtained simultaneously with intravenous catheter placement in many emergency
departments. The impact of using intravenous catheters to obtain blood cultures
is unclear.13- 16 We
hypothesized that the blood culture contamination rate would be less when
blood culture specimens were obtained from a remote site rather than through
a newly inserted intravenous catheter.
A preintervention and postintervention observational study of patients
who had a blood culture obtained as part of their routine emergency department
course was conducted. Patients 18 years old or younger who presented to the
emergency department at a free-standing tertiary care children's hospital
that evaluates more than 65 000 children annually and required a blood
culture as part of their routine care were eligible. Patients were identified
by computerized search of the hospital database.
Laboratory specimens were obtained based on clinical and laboratory
indications and were drawn by an emergency department registered nurse. The
protocols for skin antisepsis and for specimen collection and inoculation
were standardized and remained unchanged during the study. Nursing staff members
were unaware of ongoing data collection and analysis. In cases where a positive
blood culture was reported, the patient's medical record was reviewed. Patients
with indwelling devices (central venous lines, ventricular catheters) were
During the baseline phase (January 1, 1998-November 19, 1998), culture
specimens were obtained through a newly inserted peripheral intravenous catheter
using the standard over-the-needle approach. A sterile 5-mL syringe was attached
to the catheter hub, and blood for both culture and for laboratory studies
was withdrawn; the first portion of the sample was used for culture.
During the first 4 months of the baseline phase, focused efforts to
decrease the contamination rate were implemented. Because these interventions
failed to reduce the contamination rate, the standard technique was abandoned
in favor of obtaining specimens from a separate phlebotomy site. Data from
a 6-week implementation phase (November 20, 1998-December 31, 1998) were not
included in the analysis.
During the postintervention phase (January 1, 1999-December 31, 1999),
culture specimens were obtained by venipuncture at a dedicated site. If a
patient required an intravenous catheter, it was placed using the standard
approach at a site distant from the blood culture venipuncture site. While
laboratory specimens were sometimes obtained through the newly inserted intravenous
catheter, all specimens for culture were obtained by phlebotomy dedicated
to that procedure.
Blood culture isolates were categorized as contaminants or pathogens.
In all cases, Neisseria meningitidis, Streptococcus pneumoniae, Salmonella species, Haemophilus influenzae, and group A or group B β-hemolytic
streptococci were considered pathogens. A contaminant was defined as a nonpathogenic
microorganism.15 If pathogenicity was uncertain
or variable, assignment was made in consultation with an infectious disease
expert (J.R.B.), with consideration of patient demographics and the clinical
setting. Assignment was made without knowledge of the intervention phase.
Because the presence of even a single nonpathogenic species in the blood culture
specimen represented improper phlebotomy technique, a specimen with multiple
bacteria was considered contaminated.
Decisions regarding treatment and follow-up of patients were made by
clinicians in the emergency department based on current practice. The institutional
review board of the Children's Hospital Medical Center of Akron approved the
study protocol. Consent was not obtained from families. The intervention was
adopted as our standard of care, and data was collected in a blinded database
Data were analyzed using STATA Version 7.0 (Dallas, Tex, 2001). Univariate
analysis was performed unless stated otherwise. Pearson χ2 was
used to analyze categorical data. Descriptive analysis of continuous data
was performed. P<.05 was the level of significance.
Statistical process control methodology was also used to examine the
impact of the intervention over time. A run chart was constructed showing
the blood culture contamination rate for each month of the study ([number
of contaminated specimens × 100]/[number of blood cultures obtained]).
The mean blood culture contamination rate and the upper and lower control
limits were established based on the preintervention data, with control limits
representing ±3 SD from the mean.16- 18
During the study, 4448 blood culture specimens were obtained. We excluded
289 specimens obtained during the 6-week implementation phase, 14 with incomplete
data in the medical record and 37 because of the presence of central venous
catheters, leaving 4108 emergency department visits for analysis (2108 in
the baseline phase and 2000 in the postintervention phase). Overall, there
were 324 positive blood culture specimens.
Patient demographics are presented in Table 1. There were no statistically or clinically important differences
between patients in the baseline and in the postintervention phases.
During the baseline phase, 223 positive blood culture specimens were
reported; of these, 32 specimens grew a pathogen. In the 191 blood culture
specimens categorized as contaminated, 243 organisms were cultured (Table 2). The overall false-positive rate
was 9.1% and the true-positive rate was 1.5%. In the postintervention period,
there were 101 positive blood cultures; of these, 45 grew a pathogen. In the
56 contaminated specimens, 65 organisms were cultured (Table 2). The overall false-positive rate during the postintervention
period was 2.8%, with a true-positive rate of 2.3%. Using a 2-sample test
of proportions, the contaminated blood culture rate in the postintervention
phase is significantly decreased when compared with the baseline phase (P<.001). The increase in true-positive rates did not
reach statistical significance (P = .20).
The statistical process control chart (Figure 1) shows 12 consecutive data points below the mean established
in the baseline phase in the postintervention phase, indicating a special
cause effect (the intervention) and a significant change in the measured outcome
(the contamination rate).19
The contamination rates in the baseline and postintervention phases
are higher the younger the child (Figure 2). For example, in the baseline phase, the contamination rate in
patients younger than 12 weeks was 17%, compared with 4.5% in those older
than 5 years.
The contamination rates were significantly lower when blood culture
specimens were drawn from a separate and dedicated venipuncture site compared
with through a newly inserted intravenous catheter in children seen in a busy
emergency department. The low rates have been sustained since the end of the
The statistical quality control methodology we applied provides a simple
graphical display of process data that enhances our ability to understand
outcomes that occur over time.17 This methodology
has been used increasingly in the evaluation of processes occurring in the
health care setting.16,20,21 The
premise is that when a process achieves steady state, it is likely to remain
there until events cause it to shift to a new steady state.18,19
This study addresses a common problem that has been linked to substantial
and unnecessary resource utilization.9,10,22- 24 The
contamination rate in our emergency department was resistant to change in
spite of several specific interventions intended to address the problem. The
sole procedural change was in the method by which blood culture specimens
were obtained. During the baseline phase, the overall false-positive blood
culture rate was 9.1% compared with a rate of 2.8% after the intervention,
representing a decrease of 70%. While not statistically significant, the true-positive
rate increased from 1.5% at baseline to 2.3% after the intervention. We believe
that at least some of this increase is due to more selective ordering of blood
cultures during the postintervention phase, when all cultures were obtained
in response to other diagnostic tests obtained during the patient's emergency
department evaluation. Since it is easier to obtain blood for culture from
an intravenous catheter, cultures may have been obtained more indiscriminately
in the baseline phase.
Previous studies comparing contamination rates in specimens obtained
through newly inserted intravenous catheters or by phlebotomy at a remote
site suggest that the 2 techniques are essentially equivalent. Smart and Baggoley22 failed to show a difference in the contamination
rate in 940 adult patients randomized to phlebotomy by either venipuncture
or by placement of an intravenous catheter. Isaacman and Karasic14 prospectively
evaluated a convenience sample of 99 pediatric patients, each of whom had
2 blood cultures obtained, one by venipuncture and one through a newly inserted
intravenous catheter. The authors demonstrated a low contamination rate with
both techniques, concluding that newly inserted intravenous catheters offer
an alternative to a separate venipuncture procedure in patients requiring
blood culture. The small number of patients enrolled and the impact of the
nursing staff's awareness of the study protocol may have biased the results.
On the other hand, a study by Ramsook et al15 suggested
that blood culture contamination rates were decreased when using dedicated
phlebotomy compared with those obtained through a newly inserted intravenous
catheter. Importantly, this study demonstrated the highest contamination rates
in patients younger than 3 months of age, regardless of the collection method
used, a finding confirmed in our study. Because staff members were aware of
ongoing data collection, the potential effect on their phlebotomy technique
However, our study also has limitations; because medical records were
reviewed only for those patients with positive blood cultures, detailed information
about patients with negative blood cultures is not known. In particular, information
about antibiotic pretreatment is unknown. While it is likely that some patients
were prescribed systemic antibiotic therapy prior to or during their emergency
department evaluation, the rates of antibiotic pretreatment in the baseline
and postintervention phases of the study are likely to be similar and unlikely
to affect the study's conclusions. In addition, this protocol was implemented
in a single unit and may not be generalizable to other settings. Finally,
no concurrent control group was included to account for secular temporal changes.
Obtaining blood cultures from a separate site requires the patient to
undergo an additional procedure for phlebotomy, but the overall benefit in
terms of costs associated with a high contamination rate is likely to be substantial.
During the baseline period, there were 6 contaminated specimens for every
true-positive blood culture, compared with a ratio of 1.2:1 after implementation
of the intervention. If subsequent patient management is based on preliminary
blood culture results, false-positive test results will result in repeat emergency
department visits, unnecessary medical interventions, unnecessary antibiotic
therapy, and even hospital admission. One study9 found
that 26% of children followed as outpatients who had false-positive blood
cultures were hospitalized unnecessarily, and that unnecessary use of antibiotics
was significantly increased in the presence of false-positive blood culture
results. Additional costs that are more difficult to quantify include staff
effort and time required to arrange follow-up for patients, exposure of patients
to unnecessary procedures, and cost and inconvenience related to repeat emergency
department and/or hospital visits.10,24