This is a randomized trial to determine the effectiveness of a clinical decision support tool on image ordering for patients with suspected nephrolithiasis. Patients who present with acute unilateral flank or abdominal pain in whom emergency department providers suspect nephrolithiasis will receive either the clinical decision support tool or no tool (usual care).

CT scan is overused for patients who present to the ED with suspected nephrolithiasis (acute flank or abdominal pain). The investigators have developed a clinical decision support (CDS) tool to identify those patients in whom ultrasound is appropriate. The CDS tool is based on the Study of Ultrasonography vs. Computed Tomography for Suspected Nephrolithiasis in the Emergency Department.

The goal of this study is to assess the effectiveness of a clinical decision support (CDS) tool to improve advanced imaging for suspected nephrolithiasis in the ED. The investigators hypothesize those randomized to receiving the CDS tool will receive CT less often (and less radiation) compared to those receiving control. Also, the investigators hypothesize those randomized to receiving CDS will have a similar ED length of stay and rate of unexpected ED return as those receiving control.

Study design: Randomized trial of a CDS tool embedded in the electronic health record for patients with suspected nephrolithiasis. The study will be conducted at UCSF Department of Emergency Medicine.

Study subjects: The investigators will enroll adult patients who present to the UCSF ED who present with "suspected nephrolithiasis", which is defined as those with symptoms of nephrolithiasis for whom an ED provider orders a CT scan for suspected nephrolithiasis. Symptoms of nephrolithiasis include acute unilateral flank and/or abdominal pain, typically described as severe and colicky. The pain is accompanied by nausea, vomiting, and urinary symptoms, such as hematuria. The CT imaging studies emergency physicians typically order for suspected nephrolithiasis include CT scan without contrast; however a substantial minority of patients receive CT scan with contrast, and CT scan with and without contrast for acute flank pain, suspected nephrolithiasis.

Sampling, recruiting and retaining subjects: The investigators will enroll consecutive patients who present to the ED with the selection criteria. Those with suspected nephrolithiasis but have an exclusion criteria will be recorded and compared to those who were enrolled. Eligible patients will be randomized to either receiving CDS recommendations or no CDS recommendations. Subjects will not receive informed consent, and will not be contacted by staff.

Intervention: The intervention is the CDS tool, which consists of 4 components:

1. Four questions which assess the appropriateness of ultrasound for this patient
2. A link to the evidence
3. Buttons to remove CT scan and order ultrasound
4. If the CT scan order is kept, reasons why ultrasonography is not appropriate

The CDS tool will be placed or integrated into EPIC, at the point of order entry. The tool will be triggered by an order for CT to identify or rule out kidney stone.

Co-primary outcomes: Proportion of study arm who receive CT, and radiation dose. Proportion of study arm who receive CT is defined as #CT scans ordered/#patients in study arm. Radiation dose will be reported as median radiation dose in mSv. The secondary outcomes will include proportion of patients with an unscheduled return due to missed diagnosis, cost, ED length of stay.

Inclusion Criteria:

• Adult patients who present to the ED with flank or abdominal pain for whom ED provider orders a CT scan for suspected nephrolithiasis

Exclusion Criteria:

- Previous enrollment into the study

Patients, investigators, and outcome assessors will be blinded to study arm.