Overcultured? Blood cultures on discharged ED patients were ordered more frequently after the SEP-1 bundle initiation

Abstract

Introduction: In 2015, the Severe Sepsis and Early Septic Shock Management Bundle (SEP-1) tied hospital reimbursement to performance on a series of time sensitive indicators, including ordering blood cultures on patients with severe sepsis or septic shock. This metric could have broadly shaped ordering practices in the Emergency Department (ED), including for patients who did not have severe sepsis or septic shock. In this study, we sought to evaluate whether the frequency of blood culture orders on adult patients discharged from the ED changed after the SEP-1 metric, whether the rates of positivity for pathogens or contaminants changed after the SEP-1 metric, and whether similar changes were seen in orders for other laboratory tests.

Methods: This was a retrospective evaluation of blood culture orders from discharged adult ED patients from a suburban academic hospital between January 1, 2012 and June 30, 2019. We compared the number of blood cultures per discharged adult patient before and after the SEP-1 metric. We categorized each culture that grew an organism as a pathogen or a contaminant, and we compared rates of pathogen and contaminant growth before and after SEP-1. We compared rates of orders of blood cultures and lactates as labs related to SEP-1 with rates of orders of D-dimers, lipases, human chorionic gonadotropins (HCGs), and brain natriuretic peptides (BNPs) as labs unrelated to SEP-1 before and after the implementation of the SEP-1 metric.

Results: There were 144,343 adult patients discharged from the ED during the study period. A total of 6754 blood cultures were drawn from 3827 of those patient visits. The rate increased from 43.1 cultures per 1000 discharged patients before the SEP-1 metric to 75.9 blood cultures per 1000 discharged patients, an increase of 76.2% (p < 0.001). The cultures had a decreased rate of positivity (from 3.93% before SEP-1 to 3.03% after SEP-1, p = 0.044) and an unchanged rate of blood cultures resulting in a contaminant (2.49% to 1.85%, p = 0.071). Overall, orders of the labs unrelated to SEP-1 increased by an average of 16.8% after the SEP-1 metric and orders of the labs related to SEP-1 increased by an average of 81.0%.

Conclusion: After the SEP-1 bundle, blood cultures were ordered more frequently on discharged ED patients. These cultures had a lower rate of positivity for pathogens and an unchanged rate of growth of contaminants. This increase was not matched by a similar increase in other labs. Taken together, these findings suggest that the SEP-1 metric had the unintended consequence of increasing orders of blood cultures on patients healthy enough to be discharged from the ED.

Keywords: Blood cultures; Diagnostic testing; Sepsis; Utilization.