Drawing Blood Cultures from Central Lines
Yes, you should draw blood cultures from central venous catheters when catheter-related bloodstream infection (CRBSI) is suspected, but paired with a peripheral blood culture to enable accurate diagnosis using quantitative or differential time to positivity criteria. 1, 2
Recommended Collection Strategy
The optimal approach requires paired blood cultures—one drawn from the central line and one from a peripheral vein—with equal volumes collected from each site. 1, 2 This pairing is essential because:
- Quantitative blood cultures showing ≥3-fold higher colony count from the catheter compared to peripheral blood definitively diagnoses CRBSI 1, 2
- Differential time to positivity (DTP) showing growth from the catheter hub at least 2 hours before peripheral growth also confirms CRBSI 1, 2
- These diagnostic criteria cannot be applied if you only draw from one site 3
When Peripheral Access is Impossible
If peripheral venipuncture is not feasible, draw two blood samples at different times from two different catheter lumens. 1, 2 However, this approach has limitations:
- There is insufficient evidence to recommend routinely culturing all catheter lumens 1, 2
- The diagnostic accuracy is lower than paired catheter-peripheral cultures 1
- You cannot definitively diagnose CRBSI in situ without peripheral comparison 3
Critical Technical Requirements
Proper skin antisepsis is mandatory before drawing from either site:
- Use alcohol, alcoholic chlorhexidine (>0.5%), or tincture of iodine—NOT povidone-iodine 1, 2
- Allow adequate drying time to prevent contamination 1, 2
- These precautions reduce contamination rates significantly 1
Timing matters: Draw blood cultures before initiating antimicrobial therapy 1, 2
Understanding Contamination Risk
Blood cultures drawn from central lines have higher contamination rates than peripheral venipuncture (8% vs 4%), despite sterile insertion conditions. 4 This occurs because:
- Catheter hubs and connectors may be colonized with skin flora 3
- Increased manipulation during catheter access introduces contaminants 4
- This does NOT mean you should avoid drawing from catheters—it means you must interpret results carefully using paired cultures 3
Interpreting Results
The same organism must grow from both sites to diagnose CRBSI, meeting either quantitative or DTP criteria. 1, 2 Specifically:
- For quantitative cultures: catheter colony count ≥3-fold higher than peripheral 1, 2
- For DTP: catheter sample positive ≥2 hours before peripheral sample 1, 2
- Single positive cultures without comparison data are diagnostically inadequate 3
Additional Diagnostic Measures
If there is visible exudate at the catheter exit site, obtain a swab for culture and Gram staining. 1, 2 This provides additional diagnostic information beyond blood cultures.
Common Pitfalls to Avoid
Do not draw blood cultures solely from the catheter without peripheral comparison—this prevents accurate CRBSI diagnosis and leads to clinical decisions based on incomplete data. 3, 2
Do not routinely remove catheters based on positive cultures alone without considering:
- Clinical stability of the patient 1
- Presence of local infection signs (erythema, purulence at exit site) 1, 2
- Severity of illness (septic shock vs mild fever) 1
- Type of organism isolated (S. aureus mandates removal; coagulase-negative staph may allow salvage attempts) 1
Do not use povidone-iodine for skin preparation—it has higher contamination rates than alcoholic chlorhexidine or alcohol. 1, 2
Do not forget to allow antiseptic drying time—premature blood draw increases contamination risk. 1, 2
Clinical Context
The rationale for drawing from central lines is diagnostic necessity, not convenience. 3 Without catheter-drawn cultures, you cannot:
- Definitively diagnose CRBSI in situ 3
- Apply quantitative or DTP diagnostic criteria 1
- Make informed decisions about catheter retention vs removal 3
Many hospitals discourage drawing from catheters to reduce reported central line-associated bloodstream infections (CLABSIs), but this practice compromises diagnostic accuracy and patient care. 3 The guidelines explicitly recommend catheter-drawn cultures when CRBSI is suspected, regardless of reporting concerns. 1, 2, 3