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Blood Cultures

Source Blood
Mnemonic M BLOOD
Specimen Requirements

Venipuncture is the technique of choice for obtaining blood for culture. Arterial blood cultures are not associated with a higher diagnostic yields than venous blood cultures and are not recommended.
Blood culture bottles are used for collection. If other blood work is to be collected, collect the blood cultures first.

CLS staff: Refer to PX-SC710 Blood Cultures for collection instructions.

Adults (14 years old and older):

- Collect 2 SETS (4 bottles) from 2 separate sites, e.g. right arm and left arm.
- Each set consists of a green (aerobic) and orange (anaerobic) bottle.
- Always collect the green bottle first. DO NOT use yellow (pediatric) bottles for adults.

Collect 10 mL per bottle.

When an inpatient has an indwelling line, the patient care unit must collect one set from the line and may request the lab to draw the other set by venipuncture.

Pediatric collections (under 14 years old):
- Collect a yellow (pediatric) and orange (anaerobic) bottle.
- Always collect the yellow bottle first.

3 sets per 24 hour period are ONLY permitted on patients suspected of having endocarditis or endovascular infection. Collect 3rd set at least 20 minutes after initial 2 sets.

Blood Culture Bottle Descriptions and Volumes

Total volume of blood drawn depends on the patient weight and volumes required for blood tests requested. Refer to Maximum Blood Draw on Patients Weighing Less than 45 kg (100 lb) for allowable draw volumes.

Draw the MAXIMUM AMOUNT OF BLOOD into blood culture bottles whenever possible. False negative results may occur if the optimum volume of blood is not placed into the blood culture bottle.



Maximum (optimal)




10 mL

5 mL



10 mL

 5 mL



4 mL

1.5 mL*

 *Note: Acceptable minimum volume for Neonates is 1.0 mL.

Less than Optimal Volume

If it is not possible to collect the maximum (optimal) volume in all bottles, place as much blood as possible into the green bottle or yellow bottle (at least the minimum volume, but no more than the maximum), then place remaining blood into orange bottle (at least the minimum volume, but no more than the maximum).


Check the bottom of the bottle – if it is yellow, do NOT use (the bottle may be contaminated).  
- Check the expiry date (y/m/d) found on the blood culture bottle labels. If expired, DO NOT use.

- DO NOT use the "Fill" line indicated on the bottle label; it is inaccurate
- Draw two lines on bottle indicating the level of liquid in the bottle and the appropriate fill level (DO NOT overfill or underfill).-

- Disinfect bottle tops with 70% isopropanol and allow to dry for 1 minute. DO NOT use iodine.
- Use “butterfly” collection units. Syringe collection is not desirable. DO NOT use straight needle and Vacutainer. If nurses use intravascular access devices to obtain blood cultures, precautions must be taken to avoid contamination.
- If other blood work is to be collected, collect the blood cultures first.
- After selecting blood collection site, scrub the site with 70% isopropanol or Chlorhexidine gluconate solution (70% alcohol/ 2% CHG swab) for a minimum of 30 seconds. Allow to dry. Using 10% PVP Iodine or Chlorhexidine gluconate solution (70% alcohol/ 2% CHG swab), cleanse the site for 30 seconds using a circular motion, starting at the center of the site and moving outward. Allow to dry, preferably for 2 minutes, minimum 1 minute.
- If patient is allergic to 70% alcohol, use double application of PVP Iodine; if patient is allergic to iodine, use double application of 70% isopropanol. Allow to dry.
- Re-palpation of blood culture collection sites is not recommended. If re-palpation of venipuncture site is necessary to locate vein, disinfect gloved finger with alcohol and iodine (or alcohol and chlorhexidine) and perform venipuncture just above or below the re-palpation site.
- After collection, gently mix bottles by inversion to prevent clotting.
- Remove residual iodine from skin with 70% isopropanol after venipuncture.
- Ensure both bottles are labelled with the required patient identifiers. If both sets are being sent to the lab in one bag, ensure each bottle is also labelled with "number 1" for the first set and "number 2" for the second set. DO NOT cover the 2D or bottle barcode by over labeling with patient identifier or PathNet labels.

Specimen Handling

Blood Culture specimens must arrive at the DSC within 3.5 hours of receipt. Note: rural blood culture specimens arriving at the DSC within 12 hours of receipt at the rural laboratory are acceptable due to the increased time required to transport the specimen.
Keep bottles at room temperature. DO NOT refrigerate. DO NOT incubate.

Check the bottom of each collected bottle; if it is yellow, transport to DSC STAT (indicates possible growth in bottles).

Additional Information

Blood cultures should, whenever possible, be collected before administration of antimicrobial agents, therefore may be ordered and collected STAT.

Ordering physician must obtain Microbiologist approval (403-770-3757) for requests for more than 3 sets per 24 hour period, before collection.

Negative culture turnaround time:
Preliminary report - 48 hours
Final report - 5 days.

Blood Culture Interpretation Guidelines:

1.  When multiple sets of peripheral blood cultures have been obtained.

  • Staphylococcus aureus, aerobic gram-negative bacilli, group A streptococcus, yeast, and anaerobes are rarely if ever contaminants even when positive in only one set of blood cultures.
  • A single sest of blood cultures positive for Coagulase-Negative Staphylococci, viridans-group streptococci, and Bacillus species other than B. anthracis, are usually contaminants.
  • Infectious diseases consultation is strongly encouraged for all patients with Staphylococcus aureus bacteremia.

2. When paired central venous catheter and peripheral blood cultures have been obtained.

  • When multiple blood cultures  are positive from a central line only, or when the peripheral culture has a time to positivity is greater than 2 hours longer than simultaneously drawn central line, are consistent with CATHETER-RELATED bloodstream infection (CR-BSI). Catheter removal as part of management is strongly encouraged.
Testing Location CLS Microbiology
Testing Frequency Daily
Alternate Name(s)
Reference Interval