Blood cultures are performed to detect bacterial invasion (bacteremia) and the systemic spread of such an infection (septicemia) through the bloodstream. In this procedure, a laboratory technician, doctor, or nurse performs a venipuncture at the patient's bedside and then transfers the blood samples into two bottles: one containing an anaerobic (without oxygen) medium and the other an aerobic (with oxygen) medium. The bottles are incubated to encourage any organisms present in the sample to grow in the media. Blood cultures allow identification of about 67% of pathogens within 24 hours and up to 90% within 72 hours.
Although some authorities consider the timing of culture collections debatable and possibly irrelevant, others advocate two sets for those with multiple indicators of infective endocarditis, three sets with the third collected 4 to 6 hours later for suspected noncontaminant pathogens, and four sets when a common contaminant is suspected. The first of these should be collected at the earliest sign of suspected bacteremia or septicemia.
Tourniquet 
gloves chlorhexidine skin prep 20-mL syringe for an adult or adequate syringe size for a child three or four 20G 10 needles two or three blood culture bottles (50-mL bottles for adults or 20-mL bottles for infants and children) with sodium polyethanol sulfonate added (one aerobic bottle containing a suitable medium, such as trypticase soy broth with 10% carbon dioxide atmosphere; one anaerobic bottle with prereduced medium; and, possibly, one hyperosmotic bottle with 10% sucrose medium) laboratory requisition 20'' × 20'' gauze pads small adhesive bandages labels.
- Tell the patient that you need to collect a series of blood samples to check for infection. Explain the procedure to ease his anxiety and promote cooperation. Explain that the procedure usually requires three blood samples collected at different times.
- Wash your hands and put on gloves.
- Tie a tourniquet 20'' (5.1 cm) proximal to the area chosen. (See “Venipuncture,” page 89.)
Clean and dry
- Avoid contamination from skin flora for accurate testing. A recent literature review found cleansing the venipuncture site with 70% alcohol followed by 2% chlorhexidine and allowing the site to dry before puncture is effective. Start at the site and work outward in a circular motion. Wait 30 to 60 seconds for the skin to dry.
- After removing cap from culture bottles, cleanse the top with 70% alcohol and allow to dry.
- Perform a venipuncture, drawing 10 to 15 mL of blood from an adult from two different venipuncture sites to confirm culture growth. (See Blood cultures from a child.) With each specimen, activate the safety guard and discard the needle. Apply gentle pressure to the puncture site with a gauze pad for 2 to 3 minutes or until bleeding stops.
- After bleeding stops, apply an adhesive bandage.
- Wipe the diaphragm tops of the culture bottles with a povidone-iodine pad and change the needle on the syringe used to draw the blood.
- Inject 5 mL of blood into each 50-mL bottle. If both aerobic and anaerobic cultures are needed, fill the anaerobic bottle first because the organisms may take longer to grow. (Bottle size may vary according to facility protocol, but the sample dilution should always be 1:10.)
Culture ID
- Label the culture bottles with the patient's name and room number; doctor's name; and date, time, and site of collection. Verify that the information on the label matches the requisition. Indicate the suspected diagnosis and the patient's temperature, and note on the laboratory requisition any recent antibiotic therapy. Send the samples to the laboratory immediately.
- Discard syringes, needles, and gloves in the appropriate container.
- Check bottles for any signs of external contamination with blood. Decontaminate with 70% alcohol as needed.
- Remove gloves and perform hand hygiene after specimen is obtained and any spillage is cleaned.
- Obtain each set of cultures from a different site.
- Avoid using existing I.V. lines for cultures or drawing them at time of I.V. catheter insertion to decrease false-positive rates from contamination and specimens from colonized devices. (See Documenting blood culture collection.)
Outline