Detection of Bloodstream Infections in Adults: How Many Blood Cultures Are Needed?

Abstract

A blood culture is defined as a specimen of blood obtained from a single venipuncture or intravenous access device. There have been numerous changes in blood culture media and systems during the past 30 years (1,3,5,6,8). Newer media reportedly are more sensitive for the detection of microorganisms, and modern, automated, continuous-monitoring blood culture systems (CMBCSs) detect positive results 1 to 1.5 days earlier than previously used conventional blood culture systems (2, 4).Studies reported in the 1970s, 1980s, and early 1990s suggested that two to three blood cultures from adults obtained during a 24-h period could detect Ͼ99% of all bloodstream infections (BSIs) (1,5,7,8). However, a 2004 study from the Mayo Clinic using the BACTEC 9240 CMBCS found that two blood cultures detected only 80% of BSIs, that three detected 96% of BSIs, and that four were required to detect 100% of BSIs (3). This observation was unexpected given the use of a modern CMBCS and contemporary culture media. The authors hypothesized that newer systems may detect bacteremia at lower levels than older systems do and that more blood cultures are necessary to detect low-level bacteremia. To determine whether the observations were unique to the Mayo Clinic and its patient population, we systematically reviewed blood cultures at two geographically unrelated university medical centers to determine the cumulative sensitivity of blood cultures obtained sequentially during a 24-h period. MATERIALS AND METHODSAll positive blood cultures from adult inpatients at Robert Wood Johnson University Hospital, New Brunswick, NJ, and Duke University Medical Center, Durham, NC, from 1 January 2004 through 31 December 2005 were evaluated for inclusion in the study. At Robert Wood Johnson University Hospital, the BACTEC 9240 blood culture system with aerobic resin and anaerobic lytic blood culture medium was used. At Duke University Medical Center, the BACTEC 9240 blood culture system with the same medium or the BACT/ALERT blood culture system with activated charcoal medium, FA and FN, was used. A blood culture consisted of 20 ml of blood obtained either by venipuncture or from an intravenous access device. All instances in which Ն3 blood cultures per patient were obtained during a 24-h period were included. The medical records of patients who met the inclusion criteria were reviewed by one of the investigators to determine the clinical significance (true infection versus contamination) of the positive blood culture. Only patients whose positive blood cultures were judged to represent true infection were included.

The Japanese Clinical Practice Guidelines for Management of Sepsis and Septic Shock 2016 (J‐SSCG2016)

“…In addition, Lee et al . examined 629 patients whose blood culture tests yielded positive results after three or more sets were collected within 24 h; the sensitivity was 73.1% for the first set, 89.7% for the first and second sets, and 98.2% with three sets 19. Based on the above data, we conclude that a minimum of two sets (three sets, if possible) should be collected within 24 h. A further increase in test sensitivity should not be expected if the number of sets collected exceeds three.…”

Blood Cultures and Central Catheters: Is the "Easiest Way" Best Practice?

“…8,10 Optimally, 3 or 4 blood sets with adequate volume (20-30 mL) obtained within the first 24 hours of suspected bacteremia will have the greatest cumulative yield of pathogens. 11,12 (Four or more sets may be recommended when it is likely that the anticipated pathogens are common contaminants. 1 Table 2 outlines considerations for neonatal, pediatric, and adult blood culture specimens.…”

Blood Culture Sampling Practices among Internal Medicine Inpatients

“…The practice of collecting a single blood culture is contrary to recommendations of collecting 2 to 3 or more blood cultures in cases of suspected bacteremia [12,13]. Although single blood cultures have been shown to detect 91% of BSI episodes [4], they are insufficiently sensitive for detecting some bacteremias and fungemias and they are difficult to interpret [27].…”

“…Similarly, Cockerill found that while 2 blood cultures detected only 80% of bloodstream infections, 3 blood cultures detected 96% of episodes [12]. Further research by Weinstein and Reller found that 2 blood cultures obtained during a 24-hour period will detect 89-93% of BSIs in adults, while 3 blood cultures over a 24-hour period will detect all polymicrobial BSIs, and 4 cultures will detect >99.7% of unimicrobial BSIs [3,13].…”