C-175. IV Catheter-Drawn Blood Cultures: Discarding the Initial Aliquot of Blood Does Not Reduce Contamination Rates
Background: Although the preferred method for obtaining blood cultures (BC) is venipuncture, BCs often are obtained from intravenous catheters (IVC). There is no standardized method for this technique. Some authorities recommend discarding an arbitrary amount of blood (5 -10 ml) when obtaining BCs from IVC prior to inoculating BC vials to reduce contamination and remove potential inhibitory substances, but this recommendation remains unproven. It has been standard practice at Robert Wood Johnson University Hospital (RWJUH) to discard the first 10 ml of blood prior to obtaining BCs from IVC. We assessed results of BCs drawn from IVCs to determine whether discarding the initial aliquot of blood reduced contamination rates (CR). Methods: We included BCs from IVCs from adult inpatients (≥18 y) from 3/29/07-10/9/07 at RWJUH. 30 ml of blood was obtained by aseptic technique. The first 10 ml, rather than being discarded, was inoculated to a BACTEC Plus Aerobic/F blood culture vial. The second 20 ml was inoculated in 10 ml aliquots to BACTEC Plus Aerobic/F and BACTEC Lytic Anaerobic/F vials. Each positive BC was evaluated to ascertain the significance of the culture (true vs. contaminant). When appropriate, the patient’s medical record was reviewed to confirm the true versus contaminant assessment. Data were analyzed to determine whether CRs were different in the “discard” aerobic vial (D) versus the “standard” aerobic vial (S). Results: 667 BCs from IVCs were collected prospectively. Growth of contaminants was compared in the D aerobic vial matched to the S aerobic vial of the same BC. Results were as follows: both vials contaminated, 36; only D contaminated, 33; only S contaminated, 30 (P = .80, McNemar’s Discordant Pairs Test). The CR for the D vial was 10.3% versus 9.9% for the S vial (95% CI for difference in CRs, -2.8% to +3.8%). Conclusion: We conclude that it is unnecessary to discard the initial aliquot of blood when obtaining BCs from an IVC. Since discarding the initial aliquot of blood may contribute to nosocomial anemia and does not reduce CRs, this practice should be abandoned.