The detection of positive blood cultures by the BACTEC NR660. The clinical importance of four-day versus seven-day testing

Diagn Microbiol Infect Dis. Mar-Apr 1991;14(2):107-10. doi: 10.1016/0732-8893(91)90043-f.


A total of 471 positive blood cultures obtained over a 3-month period were identified and evaluated for day of positivity by the BACTEC NR660. Of all positive blood cultures, 73% (344) were detected within the first 2 days, and 94% (441) were detected through day 4. The proportion of positive cultures detected at day 5 was significantly lower than that at day 4 (p less than 0.01). Patient chart review revealed that two of 30 isolates (0.4% of all positive isolates) identified on days 5-7 were considered clinically significant and would have been missed if cultures would not have been evaluated for seven days. Therefore, very limited additional patient benefit is derived after greater than 4 days of growth and detection by the BACTEC NR660.

MeSH terms

  • Bacteria / isolation & purification*
  • Chi-Square Distribution
  • Humans
  • Sepsis / blood
  • Sepsis / diagnosis*
  • Time Factors