For all patients in the case series, factors shown to be predictive for positive FUBCs included fever on the day the FUBC was drawn, presence of a central catheter, and ESRD on hemodialysis. When broken down by persistent GPC vs. GNR bacteremia, fever, presence of a central catheter, DM, and ESRD on hemodialysis were present for GPC bacteremia, but only the presence of fever at the time the FUBC was drawn was predictive of persistent GNR bacteremia (six of eight patients).
The source of bacteremia was known in 273 (71%) patients who had FUBCs drawn. Only 37 had positive FUBCs. Broken down by source, the rate of positive FUBCs was quite low for most sources (UTI 3%, severe skin infection 6%, intra-abdominal infection 10%, osteomyelitis 0%, but higher for central catheter [34%] and pneumonia [15%]).
At our institution, FUBCs are ordered commonly, and when physicians are questioned about this practice, they are surprised to learn that this is not considered standard of care. This relatively small study goes a long way toward illuminating that this is not a very helpful practice, especially in patients with GNR bacteremia who are doing well on appropriate antibiotics. (Overall, of the 140 patients with initial GNR bacteremia, it should be emphasized that only eight had positive FUBCs.) As the authors point out, not only does ordering routine follow-up blood cultures in patients with GNR bacteremia seldom produce helpful information, but common false-positive results can lead to longer length of stay, additional inappropriate antibiotic therapy, and increased healthcare costs.