Should blood cultures be drawn from Peripherally Inserted Central Catheter (PICC) lines?

Blood Culture Collection from PICC Lines

Blood cultures should not be routinely drawn from PICC lines but rather from peripheral veins, as cultures drawn through catheters have higher contamination rates and lower specificity compared to peripheral venipuncture samples.

Proper Blood Culture Collection Technique

Recommended Approach

• When evaluating for catheter-related bloodstream infection (CRBSI), paired blood cultures should be collected:
  • One sample from the catheter (PICC line)
  • One sample from a peripheral vein
  • Both samples should be collected simultaneously 1

Diagnostic Methods for CRBSI

1. Differential Time to Positivity (DTP):

   • Growth of microbes from catheter blood at least 2 hours before peripheral blood indicates CRBSI
   • Sensitivity: 94%, Specificity: 71% 1, 2

2. Quantitative Blood Cultures:

   • Colony count from catheter blood at least 3-fold greater than peripheral blood defines CRBSI
   • Sensitivity: 80-94%, Specificity: 91-99% 1, 2

Why Not Routinely Use PICC Lines for Blood Cultures?

Contamination Risk

• Blood cultures drawn through catheters have significantly higher contamination rates (3.8-8%) compared to peripheral venipuncture (1.8-4%) 3, 4
• Despite superior sterile precautions during central line insertion, cultures taken at that time had higher contamination rates than peripheral cultures 4

Diagnostic Accuracy

• Specificity of catheter-drawn cultures (85%) is lower than peripheral cultures (97%) 5
• Positive predictive value is lower for catheter-drawn cultures compared to peripheral venipuncture 6

When PICC Line Blood Cultures Are Acceptable

Limited Venous Access

• If peripheral blood samples cannot be obtained, ≥2 blood samples should be drawn through different catheter lumens 1
• When peripheral access is impossible, cultures from two different catheter lumens at different times is an acceptable alternative 1

Negative Predictive Value

• Both catheter and peripheral cultures show excellent negative predictive values (98-99%) 6
• This means a negative result from either source is reliable for ruling out bloodstream infection

Proper Technique for Blood Collection

Skin Preparation

• Use 2% chlorhexidine gluconate in 70% isopropyl alcohol or tincture of iodine 1
• Allow 30 seconds of drying time before proceeding 1
• Alcohol, iodine tincture, or alcoholic chlorhexidine (>0.5%) should be used rather than povidone-iodine 1

Timing

• Blood cultures should be obtained before starting antimicrobial therapy 1, 2
• For suspected CRBSI, obtain 3-4 blood cultures within the first 24 hours of fever onset 1

Common Pitfalls to Avoid

1. Relying solely on catheter cultures: This can lead to overdiagnosis of bacteremia due to higher contamination rates
2. Delaying antimicrobial therapy for culture collection: Cultures should ideally be collected within 45 minutes of deciding to start antibiotics
3. Improper skin preparation: Inadequate drying time can lead to blood contamination
4. Collecting insufficient volume: Inadequate blood volume reduces culture sensitivity

By following these evidence-based guidelines, clinicians can optimize the diagnostic yield of blood cultures while minimizing false positive results that could lead to unnecessary antibiotic use and increased healthcare costs.