Blood cultures in the emergency department (ED) are frequently overused and their use does not follow recommendations and guidelines. In addition to overuse, often their clinical utility is questionable. Compounding the issues of overuse, in patients with immunocompetency and localized infections or fever without source, the diagnostic yield usually does not alter the therapeutic regimen, suggesting an overall lack of usefulness in many instances.1 Overuse, largely because of nonadherence with guidelines, results in a higher proportion of blood cultures and laboratory tests lacking clinical effect. Curbing overuse is an important step in addressing this.
“From a very broad interpretation, overuse of laboratory tests is undoubtedly an issue. If you look at just the number of complete blood counts and chemistry that we run, clearly there is an overreliance on it. I think a lot of clinicians have become accustomed to checking these [laboratory values] daily or multiple times per day. In patients who are critically ill, such vigilance is important, but as a patient becomes more stable, it’s really not necessary to continue forward with that intensity of checks,” explained Mark E. Rupp, MD, professor and chief of the Division of Infectious Diseases at the University of Nebraska Medical Center in Omaha, Nebraska, in an interview with Infectious Disease Advisor.
Blood Culture and Infections of the Skin and Soft Tissues: In the Age of Methicillin-Resistant Staphylococcus aureus
Infections of the skin and soft tissue (SSTIs) are increasingly causing visits to EDs, along with correlated increases in hospitalizations.2
In 2005, the Infectious Diseases Society of America (IDSA) issued guidelines for the management of SSTIs, with updates in 2014. Although not prospectively validated, the guidelines address when blood cultures are needed in SSTIs, particularly as infections with methicillin-resistant Staphylococcus aureus (MRSA) are increasing in rate and are especially concerning.3,4
The IDSA guidelines emphasize the need for prospectively validated studies that clearly define severity of infection and couple it with issues in treatment and outcomes. In that absence, the guidelines recommend when patients with SSTIs should undergo blood draws and what laboratory tests should be run from those draws. They also recommend that patients with severe SSTI should be hospitalized and patients with mild SSTI should not.3,4
In actual practice, adherence with these guidelines is lacking. A recent study in Open Forum Infectious Diseases assessed records from 214 patients with SSTIs in the ED at a tertiary hospital. In only 20.1% of cases were the IDSA guidelines for the management of SSTI followed. Of the 104 patients with mild-severity SSTI, 21.1% were admitted (n=22), and of the 59 patients with severe SSTI, 33.9% (n=20) were discharged.2
IDSA guidelines recommend blood cultures only in severe cases of nonpurulent infection. In 70 patients with mild cellulitis, 28.6% (n=20) had blood cultures drawn. Of these, 1 blood culture (5%) was positive for methicillin-sensitive S aureus. In 71 patients with moderate to severe cellulitis, 57.7% had blood cultures (n=41) with only 1 culture (2.4%) positive for S pyogenes.2
“[T]he results of the present study show a striking lack of adherence to published guidelines,” the authors wrote. The authors suggested a possible explanation to the discrepancy in clinical treatment and guideline recommendations, indicating that perhaps “the guidelines are difficult to interpret, do not fit individual circumstances, or do not include other approaches that are based on evidence or good clinical judgment.”2
Dr Rupp described the importance of stratifying patients with MRSA based on whether bacteremia has cleared by days 2 to 3 of treatment, with patients with cleared infection needing 2 weeks of antibiotics and those with continued bacteremia needing 4 to 6 weeks of antibiotics. “It’s really important to make that designation,” Dr Rupp explained.
He continued, “Now, people have extrapolated from that into anybody with any sort of bacteremia. This is occurring widely across institutions. Clinicians have extrapolated from that experience with MRSA and have applied the same therapeutic approach to patients with, for example, gram-negative bacilli bacteremia or other types of bacteria in their bloodstream. That’s really not the best practice.”
Blood Cultures and Clinical Utility: Pediatric Populations
Although volume of blood collected for detection of a pathogen is as important in the pediatric population as it is in the adult population, collecting enough blood can be challenging in children. Volumes between 0.5 and 1.0 mL, common for blood cultures in this population, are unlikely to be large enough to detect the low-level bacteremia common in children. What’s more, low volume at collection is inversely correlated with contamination of samples.5
Although IDSA recommends 2 to 4 blood culture sets per septic episodes for adult patients, this recommendation in children is not always feasible because of children’s smaller size. Even in larger children, collection of more than 1 set, which could help rule out contamination, is uncommon. Additionally, evidence suggests that obtaining sufficient blood volume in a single blood draw is more important than obtaining multiple blood draws.5
Additionally, nonadherence to guidelines and protocols for collecting blood cultures with limited clinical utility extend beyond affecting adult populations. A 2014 retrospective study in a pediatric ED in Spain assessed medical records and results of blood cultures from 2062 pediatric patients without risk factors for bacteremia such as having prosthetic valves.1
Of the blood cultures collected, 26.6% were not collected according to protocol. None of these blood cultures had diagnostic yield. In comparison, 2.7% of blood cultures were collected according to protocol had diagnostic yield. Fever without source accounted for most of the nonadherence.1
In a study of 2705 pediatric patients with community-acquired pneumonia treated at an ED in Korea, just 30.8% of patients had blood cultures justified by IDSA guidelines. Only 0.4% of blood cultures resulted in positives for infection (n=12).6 IDSA guidelines are standardized for adult populations, suggesting the creation of guidelines specific to the pediatric population could help clarify how to best treat this group of patients and could improve adherence.
Of the 12 samples positive for infection, 58.3% were justified by guidelines (n=7) and just 3 samples were positive for S pneumoniae. Additionally, 2 of 3 patients whose samples were positive for S pneumoniae had previous positive blood cultures from referring institutions. No blood culture-directed changes in antibiotics occurred.6
“We found a low utility of [blood culture] for the diagnosis of bacteremia in a highly selected population,” wrote the authors. They continued, “Judicious use of [blood culture] can decrease unnecessary venipuncture and antibiotic treatment.”6
Decreasing Excessive Blood Cultures by Limiting False Positives
When blood cultures are indicated, decreasing contamination to prevent false positives becomes a major concern. False positives in blood cultures introduce a variety of toxicities into caring for the patient, from side effects of unnecessary medication to financial toxicity on the healthcare system and the patient.
Additionally, false positives can foster additional, ultimately unnecessary, blood cultures to be drawn. In a recent study published in Clinical Infectious Diseases, use of an initial specimen diversion device, Steripath® (Magnolia Medical Technologies, Seattle, WA), in an ED in 904 patients and 1808 paired blood cultures, false positives were significantly reduced from 1.78% with standard phlebotomy (n=16/904) to an impressively low 0.22% with Steripath (n=2/904; P =.001).7
Steripath diverts the first 1 to 2 milliliters of blood, limiting microorganisms that find sanctuary in the sebaceous glands, hair follicles, and cornified skin from contaminating the sample.6
Dr Rupp, who was first author on this study, explained, “Now with regard to Steripath, with its initial specimen diversion, if you don’t have the false positive, contaminated blood culture in the first place, then the clinicians are not concerned about showing that the bloodstream has been sterilized or about repeating the culture to determine if the first blood culture really was contaminated.”
This, ultimately, can decrease total number of blood cultures, particularly repeated blood cultures.
“Our results were very profound, and we reached a very low rate of contamination. I’m confident that if we were to use that in a generalized fashion across the board in everybody, we would decrease our rates of contamination,” concluded Dr Rupp.
Training on adherence to guidelines, the development of guidelines specific to the pediatric population, and the employment of tools and techniques to decrease contamination of blood cultures could decrease the overuse of blood cultures, improve the quality of the clinical information derived from blood culture results, improve clinical outcomes, and decrease healthcare costs.
- Astete JA, Batlle A, Hernandez-Bou S, Trenchs V, Gené A, Luaces C. Blood culture diagnostic yield in a paediatric emergency department. Eur J Emerg Med. 2014;21(5):336-340.
- Kamath RS, Sudhakar D, Gardner JG, Hemmige V, Safar H, Musher DM. Guidelines vs actual management of skin and soft tissue infections in the emergency department. Open Forum Infect Dis. 2018;5(1):ofx188.
- Stevens DL, Bisno AL, Chambers HF, et al; Infectious Diseases Society of America. Practice guidelines for the diagnosis and management of skin and soft-tissue infections. Clin Infect Dis. 2005;41(10):1373-1406.
- Stevens DL, Bisno AL, Chambers HF, et al; Infectious Diseases Society of America. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America. Clin Infect Dis. 2014;59(2):147-159.
- Bard JD, TeKippe EM. Diagnosis of bloodstream infections in children.
- J Clin Microbiol. 2016;54(6):1418-1424.
- Kwon JH, Kim JH, Lee JY, et al. Low utility of blood culture in pediatric community-acquired pneumonia: an observational study on 2705 patients admitted to the emergency department. Medicine (Baltimore). 2017;96(22):e7028.
- Rupp ME, Cavalieri RJ, Marolf C, Lyden E. Reduction in blood culture contamination through use of initial specimen diversion device. Clin Infect Dis. 2017;65(2):201-205.