Which blood cultures and laboratory tubes (including tube types and bottle sizes) should be drawn before starting antibiotics in a patient, specifying adult versus pediatric collection?

Blood Culture Collection: Specimens and Tube Types Before Starting Antibiotics

Draw 2-3 sets of blood cultures before initiating antibiotics, with each set consisting of one aerobic and one anaerobic bottle in adults (20-30 mL total per set), and 1-2 aerobic bottles in children with age-appropriate volumes. 1

Adult Blood Culture Collection

Number of Sets and Bottle Types

• Collect 2-3 blood culture sets from separate venipuncture sites before starting antibiotics 1
• Each set requires at least one aerobic bottle (8-10 mL) and one anaerobic bottle (8-10 mL) 1, 2
• Total blood volume per set should be 20-30 mL 1, 2
• If only ≤10 mL can be obtained, inoculate into a single aerobic bottle only 1

Bottle Filling Order

• Fill the aerobic bottle first, then the anaerobic bottle 2
• Most pathogens grow aerobically, though Streptococcus pneumoniae and some gram-positive organisms may grow best in anaerobic bottles 1

Critical Technical Points

• Volume is more critical than timing for diagnostic yield 1
• Disinfect venipuncture site with chlorhexidine or 2% iodine tincture, allowing 30 seconds drying time for chlorhexidine/alcohol or 2 minutes for povidone-iodine 1, 2
• Wipe bottle injection ports with 70-90% alcohol before inoculation 2
• Never refrigerate blood prior to incubation 1

Pediatric Blood Culture Collection

Age-Based Volume Requirements

The following volumes represent total blood per culture set: 1

• ≤1 kg: 2 mL total (single bottle, Culture Set #1 only)
• 1.1-2 kg: 4 mL total (2 mL per set × 2 sets)
• 2.1-12.7 kg: 6 mL total (4 mL Set #1 + 2 mL Set #2)
• 12.8-36.3 kg: 20 mL total (10 mL per set × 2 sets)
• >36.3 kg: 40-60 mL total (20-30 mL per set × 2 sets)

Bottle Selection for Children

• Use 1-2 aerobic bottles only for pediatric patients 1
• When ≤10 mL is collected, use a single aerobic bottle 1
• For children 2.1-12.7 kg (most toddlers), aim for 6 mL split between 2 bottles when possible 3

Pediatric-Specific Considerations

• Do NOT use chlorhexidine in children <2 months old; use 2% iodine tincture instead 1
• Multiple blood cultures with adequate volume significantly improve pathogen isolation rates and antimicrobial stewardship decisions in children 4

Common Pitfalls to Avoid

Venipuncture Site Selection

• Avoid drawing through indwelling catheters when peripheral venipuncture is possible—catheter-drawn cultures have significantly higher contamination rates (false positives) 1, 2, 3
• Obtain cultures from separate venipuncture sites for each set 1

Timing Considerations

• Draw all blood cultures before starting antibiotics whenever possible 1, 2
• In critically ill patients requiring immediate antibiotics, draw 2-3 sets simultaneously from different sites within <1 hour 1, 5
• IV antibiotics can sterilize blood cultures within hours of administration 6

Volume Errors

• Inadequate blood volume is the most common error that markedly reduces diagnostic sensitivity 1, 2
• Contamination rates should not exceed 3% (target <1%) 1, 3, 7
• Insufficient volume leads to false-negative results even when bacteremia is present 1

Additional Laboratory Tubes

While the question focuses on blood cultures, if additional laboratory testing is needed:

• Standard laboratory tubes (e.g., lavender/EDTA for CBC, gold/SST for chemistry) should be drawn after blood culture bottles to maintain sterility and adequate culture volume 2
• Blood culture collection takes priority over other specimens including arterial blood gases when infection is suspected 2