<p>Standing orders allow triage nurses in emergency departments (EDs) to order tests for target patients prior to a physician evaluation. Standing orders specify the medical conditions for which a triage nurse is permitted to order tests but typically do not specify the operational conditions under which ordering tests is desirable, from either a system or a patient point of view. We examine the operational impacts of standing orders on the ED as a whole, and propose a threshold policy for activating standing orders as a function of ED congestion. To parameterize the threshold policy we develop three simplified models: 1) an infinite-server model to derive an easily-computed feature for predicting whether activating standing orders would be beneficial, 2) a Jackson network model, to demonstrate that standing orders can lead to diverse outcomes for different patient populations, and 3) a Markov decision process model, to quantify the optimality gap for our threshold policy. We confirm the tentative findings from the simplified models in a more realistic setting using a simulation model that is calibrated with real data. We find that the threshold policy, with a threshold that is a simple function of the aforementioned feature, performs well across a wide range of parameter values. We demonstrate potential unintended consequences of the use of standing orders, including overtesting and spillover effects on non-target patients. Medical studies demonstrate that the use of standing orders decreases average ED length of stay (LOS) for target patients. Our research shows the importance of investigating the impact of standing orders on the ED as a whole.</p>