The “Emergency Department Pathology Order Support Tool” (ED-POST) is an electronic laboratory test ordering decision support tool that aims to decrease variation in test ordering practices. As part of a larger project on the co-design, development, and evaluation of ED-POST, this study aimed to explore the workflow nuances that might affect the intended use of the digital decision support tool. Semi-structured, in-depth interviews were conducted with 15 ED clinicians involved in the laboratory test ordering process across the development and evaluation phases of ED-POST. Participants identified the expanded role of registered nurses in test ordering and the practice of ordering tests that are outside the ED’s scope as contextual characteristics that can affect the use and perceived utility of the proposed ED-POST tool. Reconciling “work-as-imagined” with “work-as-done” in the design and development of electronic interventions is important in achieving interventions to improve the safe and effective use of pathology tests.