Feasibility and Impact of a Decision Rule for Imaging of Emergency Department Patients With Suspected Kidney Stone

Patients that a clinician deems a CT Flank Pain Protocol for suspected kidney stone is warranted based on their usual practice will be eligible for enrollment. Clinicians will be encouraged to page the Research Associate (RA) prior to ordering the CT, and an automatic page will go out for all CT flank pain protocols that are ordered via EPIC. RAs will approach eligible subjects for written informed consent. Subjects who are incapable or unwilling to provide informed consent, including non-English speaking patients will be excluded.

Following written informed consent, eligibility for the S.T.O.N.E. score will be determined.

Subjects that consent to enrollment but have exclusion criteria will be enrolled observationally to determine the performance of the S.T.O.N.E. score and outcomes in these groups, but will not be eligible for alternate imaging pathways.

Subjects who do not have any of the above exclusion criteria will be placed in one of three groups based on the S.T.O.N.E. score (which may be supplemented by gestalt clinician pre-test probability and/or point-of-care ultrasound for hydronephrosis). The groups are low, moderate, or high and correspond to the likelihood of the patient having a kidney stone as described in results from phases I and II.Subjects in the "high" likelihood of stone group will be eligible to get either Ultra Low Dose Computerized Tomography (ULDCT) or "expectant management". The choice will be determined by the primary clinician in conjunction with the patient. If ULDCT is elected, the scan will be read diagnostically by the radiologist and the clinician will treat the patient based on these results. If the expectant management option is chosen, no CT will be done during the ED visit and they will be treated as if they have a kidney stone. We will attempt to contact these patients at \~1 week after their ED visit, and they will also have the option to contact our study team. If symptoms are persistent for a week or more, subjects may of course pursue further clinical care with the clinician of their choice and this will not be billed to the study.

Subjects in the "moderate" likelihood of stone group will be given the option to receive either a standard dose CT or ULDCT. Again, the decision of which imaging option to choose will be made by the primary clinician in conjunction with the patient.

In the "low" likelihood of stone group the RA will present the data from the stone score to the physician and explain that patient is unlikely to have a kidney stone and they will be advised that probability of a stone is very low and that alternate imaging choices may be warranted. If they still choose to order a CT Flank Pain Protocol they will be asked to provide reasoning and the patient will receive a regular dose CT Flank Pain Protocol.

All subjects will be followed during their Emergency Department (ED) course and follow-up care (records in EPIC), with an attempt to contact the patient at \~90 days after the initial ED visit. Outcomes will include the number of eligible patients that receive regular dose CT, ULDCT, or the expectant management option. Radiation dose received will be measured with comparison of both the expected radiation dose if regular CT had been performed in all eligible patients and using a before and after model from phases I and II. We will also follow all patients to determine the prevalence and timing of diagnosis and/or intervention for kidney stone or other pathology. We will qualitatively compare the prevalence of alternative causes of symptoms and incidental findings (and follow-up) for regular and low dose CTs.