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Table 8.6 Diagnosing CABSI by differential time to positivity

1. Blood culture performed with aerobic and anaerobic blood culture bottle from central venous catheter and peripheral site respectively.
2. Approximately equal volume of peripheral blood and catheter blood (from ALL lumens) should be drawn simultaneously under aseptic technique.
3. Label clearly “Suspected catheter associated blood stream infection” to alert laboratory staff so that all bottles are incubated into the continuous monitoring blood culture system at the same time.
4. The time for blood culture broth to turn positive is recorded. (The TTP can be obtained from microbiology laboratory)
5. If catheter blood TTP is >2 hours early than peripheral blood TTP, then the patient is likely to have CABSI.
6. The differential time to positivity is valid only if:
  • The volume of peripheral blood injected into the blood culture bottles is approximately equal to the catheter blood
  • Blood culture are taken simultaneously
  • Blood culture are incubated into the blood culture system at the same time