|
Beth
Israel Deaconess Medical Center
Laboratory
Manual
|
Back to Specimen
Collection
Back to Main
Page of Lab Manual
Go directly to: routine blood cultures
, timing and number , Bartonella , mycobacteria/dimorphic
fungi
Obtaining
Routine Blood Cultures
- Assemble equipment, wash hands,
and put on gloves.
NOTE: Check all expiration dates
of blood tubes/blood culture bottles before drawing blood. Do not use
expired tubes/blood culture bottles. Discard all expired media appropriately,
i.e., dispose glass containers in a sharps container. -
Select site and apply tourniquet.
- Vigorously scrub the skin over
the planned venipuncture site in a circle approximately 8 cm (3 inches) in
diameter with a sterile 70% isopropyl
alcohol wipe and allow to air dry completely.
- Perform the skin
scrub two additional times.
| Inadequate
preparation of the skin prior to a venipuncture for blood culture collection
which results in growth of skin or environmental flora can increase the cost
of intravenous antibiotics by 39% and the length of stay by 4 days (JAMA,
1991; 265:365-9). In this report, overall hospital charges for a contaminated
blood culture were $4400 greater than costs for a patient with a true positive
blood culture. |
- Perform venipuncture (see "Instructions
for Performing Venipuncture") and withdraw 20 ml of blood.
- Swab bottle septa (they are
not sterile) with alcohol and allow to dry.
- Inject 8-10 ml (minimum acceptable:
3 ml) into 1 bottle and 8-10 ml (minimum acceptable: 3 ml) into the other
bottle. Changing needles between bottles is not necessary. (When less than
20 ml of blood is available for culture, split the blood evenly between the
two bottles.)
Comments
The recommendations
for collecting blood cultures summarized below are designed to optimize the
detection of bacteremia while eliminating unnecessary, excessive cultures.
- No less than 2 and no more than
3 separate blood culture sets should be drawn in any 24 hour period. The
yield from 3 blood cultures in a 24 hour period has been shown to be 99.9%
for all types of bacteremia.
- Culture sets should be taken
from separate venipuncture sites as soon as possible after the onset of fever
or chills. Spacing the blood cultures during the 24 hour period may be helpful
for documenting continuous bacteremia in patients with suspected endovascular
infections, such as endocarditis.
- Always obtain at least 2 (and
no more than 3) separate cultures prior to beginning antibiotic therapy.
- Wait at least 48 hours after
obtaining the initial blood cultures before obtaining any additional ones.
If blood cultures are still negative after 48 hours and the patient’s clinical
condition warrants it, draw two more blood cultures over the next 24 hours.
Discussion with the Laboratory Director on-call to discuss other diagnostic
strategies may be appropriate at this time.
- Current methods for culturing
blood have been documented to be capable of detecting fastidious, slower
growing organisms such as Viridans streptococci and HACEK group members (Haemophilus
aphrophilus, Actinobacillus, Cardiobacterium, Eikenella and Kingella) within
the routine 5 days of incubation. Therefore, extending incubation for blood
cultures is of limited utility and is not generally done. Note, however,
that Brucella takes longer to grow and therefore, when Brucella is suspected,
a Brucella blood culture must be specifically requested and will be held
for 10 days. When isolated, most Brucella cultures flag as positive
within six days based on published experience with our blood culture system.
Brucella serological analysis should also be requested because of suboptimal
sensitivity of culture.
Blood cultures for mycobacteria and dimorphic
fungi
- Prepare skin as described for
routine blood cultures.
- Perform venipuncture and inoculate
3 to 5 ml of blood (5 ml maximum, 1 ml minimum) into Myco F/Lytic Bactec
bottles. Do not inoculate more than 5 ml of blood.
- One or two samples per week
are optimal for both fungemia and mycobacteremia detection.
- Note: yeasts (e.g., Candida) are
generally detected using standard blood culture bottles.
- Blood cultures for Malassezia
(e.g., in patients on total parenteral nutrition) should be sent in a Myco/F
Lytic bottle with culture of this organism specially requested. Furthermore,
to optimize yield, blood should be drawn through the catheter used to administer
TPN.
Blood culture for Bartonella
Bartonella blood cultures have
extremely low yield, only a few have been isolated from blood across the
world, none at BIDMC. Prior antibiotic therapy precludes isolation.
Therefore, this test is no longer available at BIDMC. Serology recommended
instead.
Revised/reviewed 3/12/2010
Back to
Main Page of Lab Manual