Introduction

Urolithiasis is a common cause of emergency department (ED) presentation, accounting for over 1 million visits and $5 billion in health care expenditures annually in the United States.¹ Acute management in the ED requires identifying patients who require admission vs candidates for expectant management. While sepsis from obstructive pyelonephritis is a clear indication for admission and urgent decompression, poor pain control, nausea/emesis, and azotemia are more nebulous. For these patients, continued assessment may be warranted for proper disposition, yet utilization of inpatient beds may not be the most judicious use of hospital resources.

The observation unit (OU) is an adjunct to emergency care by serving as an intermediary between hospital admission and prolonged occupation of emergency beds. Studies have demonstrated OU utilization results in comparable health outcomes to inpatient admission, while decreasing length of stay and lowering hospital costs for conditions such as acute coronary syndrome, heart failure, and obstructive pulmonary diseases.^2-4 To the best of our knowledge, we provide the first examination of OU utilization for renal colic and examine clinical factors that may predict inpatient hospital admission.

Methods

A retrospective, Institutional Review Board–approved study of patients with renal colic observed in the OUs of 2 tertiary care EDs between January 2014 and December 2015 was performed to compare patients requiring admission to those discharged following OU stay. Admitting diagnoses of calculus of the kidney, calculus of the ureter, and/or renal colic (ICD-9 592.0, 590.1, and 788.0) with radiographic evidence of obstructive urolithiasis were included. Criteria for placement into the OU was at the discretion of the treating ED physician, typically with urology consultation. Clinicodemographic data including age, gender, history of urolithiasis, laboratory data, imaging findings, analgesia usage, and disposition following OU stay were examined. Average Medicare reimbursement with Diagnostic Related Group 694 and Ambulatory Payment Classification 8011 was used to estimate inpatient and outpatient costs, respectively. Fisher’s exact test, Mann-Whitney U test, and multivariable analysis using binomial regression were utilized for statistical analysis with P < .05 as significant.

Results

Eighty-five patients with renal colic observed in the OU qualified for analysis. Subjects had a mean age of 51.3 years (SD 13.4) with slight male predominance (58%) and urolithiasis history in nearly half (58%; Table 1). Following OU stay, 10 patients (12%) required admission for uncontrolled pain (50%), worsening renal function (30%), fever (20%), and infection (10%). Seven admitted patients underwent intervention, including ureteral stent (n=4) or ureteroscopy (n=3). Nearly 85% of the 75 discharged patients did not return to the ED within 30 days. Of these, 23 patients had follow-up data and underwent successful surveillance or definitive therapy. Eleven (14.6%) of the discharged patients returned to the ED within 30 days, and only 6 required operative intervention.

Only serum creatinine ≥1.5 mg/dL was significantly associated with admission (60% vs 24%, P = .027; Table 2). Other factors such as previous ED visit within 30 days, age, leukocytosis, stone size ≥5 mm, analgesia requirements, and proximal stone location were not associated with admission. On multivariate analysis only azotemia was significantly associated with admission. The average Medicare payment for Diagnostic Related Group 694 in fiscal year 2016 was $5,457.80, while the equivalent payment for Ambulatory Payment Classification 8011 was $1,813.30. Total Medicare cost savings approximated of OU utilization was $273,982 for this cohort.

Discussion

OUs have demonstrated both safety and efficacy as well as cost savings in various clinical conditions. Madsen et al prospectively examined UO utilization for chest pain evaluation in geriatric patients and found no adverse events in those discharged, suggesting patients at high risk for readmission may be safely managed in an OU following careful patient selection.⁵ Another study demonstrated that implementation of an atrial fibrillation treatment algorithm in the OU decreased admissions without an increased risk of readmission.⁶ Similarly, our data suggest that renal colic can be safely managed in the OU. An inpatient admission for uncomplicated renal colic can cost up to 4 times that of an ED visit.⁷ A review of claims data for patients presenting to the ED with chest pain found that OUs saved $1,535 per patient compared with inpatient admission.⁸ Similarly, when using the 2016 Centers for Medicare & Medicaid Services standard payment database, each patient differs by $3,644.50, which represents a substantial saving to the health system overall.

We found most patients (88%) treated in the OU avoided hospital admission, and of those admitted, 70% underwent intervention during hospital stay. Our admission rate is consistent with the 12% admission rate described in a large population study of over 3 million ED visits for upper urinary tract stones.¹ The high rate of inpatient surgical management following hospital admission from the OU in our cohort demonstrates the OU’s ability to screen for patients who truly warrant inpatient management. A recent study examining >1 million ED visits for uncomplicated renal colic found that 8% of patients were admitted and only 6% required urological procedures during hospitalization.⁷ It is possible that the use of an OU could have reduced inpatient hospitalizations given the rate of nonintervention by identifying patients who may be discharged from those who would likely require intervention.

Our study, of course, is not without limitations. First, the retrospective nature and lack of criteria for OU admission increase the risk of selection bias. Second, management in the OU was not based on a specific protocol, and thus discharged patients may have undergone more efficacious treatment. Lastly, follow-up was unfortunately limited as patients were not required to seek urological care within our hospital network.

Conclusions

Our study found that most patients with renal colic observed in the OU can be discharged home without requiring admission or intervention. The OU was a useful intermediary between discharge from the ED and admission to an inpatient unit for equivocal cases and has potential to significantly decrease health care costs. Prospective studies with defined criteria for OU admission, management protocols, and adequate follow-up are needed before widespread adoption of OU utilization for acute renal colic.

Support: None.

Conflict of Interest: None.