Comparison of BacT/Alert and BACTEC NR 860 blood culture systems in a laboratory not continuously staffed

Objective: To evaluate the performance of continuously working blood culture systems in a discontinuous laboratory system. Methods: The systems used were BacT/Alert (Organon Teknika Corp., Durham, NC) and BACTEC NR 860 (Becton Dickinson Diagnostic Instruments, Sparks, Md) in a comparison in a laboratory staffed 8 1/4 h on Mondays to Fridays and 4 1/4 h on Saturdays. Blood culture bottles (BacT/Alert aerobic and anaerobic, BACTEC NR 26 A and NR 27 A) were received thrice daily. Results: From 1824 pairs of blood culture vials, 110 clinically significant microorganisms were recovered by both BACTEC and BacT/Alert, 43 by BACTEC alone, and 33 by BacT/Alert alone. The differences between the systems in total recovery and in recovery of individual species were not statistically significant. The average detection times were 13.36 h for BACTEC and 13.93 h for BacT/Alert (P > 0.1). These times represent only 35.6% (BACTEC) and 32.6% (BacT/Alert) of the total timespans from collection of blood to informing the ward of a positive result (t(crd), clinically relevant detection time). If 24 h per day blood culture processing conditions and continuous transport of vials to the laboratory had been available, these percentages would have risen to 87% (BACTEC) and 87.5% (BacT/Alert). Under such 'ideal' conditions, t(trd) could have been reduced by 22.16 h using BACTEC and by 26.81 h using BacT/Alert. The BacT/Alert system showed more false-positive results than the BACTEC system (80 (4.39%) versus 23 (1.26%), P < 0.001). Conclusions: No time benefit for detection of positive blood cultures is gained with continuously measuring systems, if loading and processing of vials is organized discontinuously, as in our laboratory.