The Small Acute Ureteral Stone Protocol: Clinical Outcomes and Relapse Patterns

Abstract

Purpose:

Nephrolithiasis affects approximately 10% of North Americans, placing a significant burden on health care systems. This study evaluates the effectiveness of a novel, virtual Small Acute Ureteral Stone (SAUS) protocol for managing ureteral stones ≤5 mm, aiming to optimize resource utilization and patient care.

Materials and Methods:

A retrospective review was conducted on 209 consecutive patients enrolled in the SAUS protocol from June 2018 to May 2019. The protocol included follow-up renal bladder ultrasound and nurse case manager telephone assessment. Patients were followed for a median of 5.4 years, with data collected on stone passage rates, interventions, and long-term outcomes.

Results:

The SAUS protocol successfully redirected 53% of patients from urgent clinic visits. Of these, 98% did not necessitate urologic intervention for their small ureteral stone. Overall, 77% of patients showed radiographical confirmation of stone passage, and 74% reported being symptom-free. Only 13% of all patients underwent intervention for their initial ureteral stone. Long-term follow-up revealed that after discharge from our protocol, 67% of patients did not re-present over 5 years, and 90% remained free from urologic intervention. The study’s retrospective nature and reliance on electronic medical records may have introduced bias. Patient adherence to follow-up recommendations varied, potentially affecting outcome accuracy.

Conclusion:

The SAUS protocol demonstrates effectiveness in virtually managing small ureteral stones, reducing unnecessary clinic visits and interventions. The protocol’s success suggests its potential for implementation in similar clinical scenarios, potentially reducing health care costs and improving patient care in urolithiasis management.

Introduction

Nephrolithiasis is a common condition affecting approximately 1 out of 10 people in North America.¹ In 2006, nephrolithiasis cost the U.S. health care system over $10 billion USD. The management of kidney stones is becoming increasingly burdensome because of the pervasiveness, recurrence, and the increasing prevalence of nephrolithiasis.^2,3

Our academic urology practice consists of 18 adult urologists and receives approximately 150–400 consults for acute obstructing ureteral stones each month.⁴ Historically, patients with an acute ureteral stone were referred from an emergency department (ED) or their primary care physician (PCP) office and seen within our Acute Stone Clinic (ASC) by one our endourologists within 1–2 weeks of their initial renal colic episode.⁴ Within a prior publication examining our ASC, we identified that a large proportion of patients with ≤5mm stones missed their appointments often citing symptom resolution or spontaneous stone passage as the most common reason for not attending.⁴ These missed appointments create lost opportunities for other patients to receive timely care.

To accommodate a large burden of consults and optimize appointment utilization, a small acute ureteral stone (SAUS) protocol was designed. The goal of our protocol was to focus our efforts and limited clinic resources on the patients with a lower likelihood of spontaneous stone passage and a higher likelihood of necessitating urologic intervention. Patients with stones >5 mm were routed into our standard ASC pathway, and those patients referred with small ureteral stones (≤5 mm) were enrolled in our SAUS protocol. A maximal stone diameter of ≤5mm was chosen for our protocol given an approximately 75% likelihood of stone passage with conservative management alone.⁵

To our knowledge, no similar protocol has been previously described in the literature, leaving its utility unexplored. This study aims to review the clinical outcomes of patients enrolled in our virtual SAUS protocol. Secondary objectives included patient reported stone-free and pain-free rates, initial patient disposition, as well as resource utilization, including long-term patient re-presentation and urologic intervention.

Materials and Methods

SAUS protocol

All stone referrals to our ambulatory urology clinic are triaged by an endourologist. Patients referred with an obstructing ureteral stone that is ≤5 mm in maximal diameter are triaged into the SAUS protocol (Fig. 1). Patients with a concern for a urinary tract infection, an obstructed solitary kidney, bilateral obstructing ureteral calculi, grossly deteriorated renal function, and/or concurrent pregnancy are excluded from the SAUS protocol. As part of the protocol, a follow-up renal bladder ultrasound (RBUS) is ordered (within 2–4 weeks) and patients are contacted by a nurse case manager telephone symptom assessment. All patients are provided a prescription for Flomax at the time of this phone call. Patients and PCPs are educated on reasons to contact the urology clinic and or return to the ED through a templated letter. In addition, patients and their PCP are reassured that most stones of this size are anticipated to pass spontaneously. Patients are advised of the importance of confirming stone passage via repeat imaging as opposed to simply relying on resolution of symptoms.⁶ Once the follow-up imaging is performed, a follow-up phone call with a nurse case manager is scheduled. If the patients are deemed to be stone-free on follow-up ultrasound imaging and have no further symptoms, the patient then has the option to be discharged to their PCP or to see a urologist in the elective stone clinic (ESC) to discuss stone prevention measures on a nonurgent basis. All SAUS protocol registered nurse follow-up phone call encounter documentations are routed to and reviewed by the triaging urologist prior to patient discharge from our protocol. If patients have features suggestive of ongoing ureteral obstruction or residual symptoms, they are then booked for an ASC appointment with an endourologist within 1–2 weeks of their ultrasound and symptom assessment.

FIG. 1.

Workflow for SAUS protocol. SAUS, Small Acute Ureteral Stone.

Patients

We performed a retrospective review of all patients who entered the SAUS protocol in the first year after its initiation (June 1, 2018–May 31, 2019). Adult patients were identified at the time of their SAUS virtual appointment from our electronic medical record and were included if initial imaging demonstrated the presence of an obstructing ureteral stone ≤5 mm in maximum diameter. In total, 209 consecutive patients were included, with all data collected in an encrypted REDCap database. Patient follow-up data were collected using our universal province-wide electronic medical record from June 2018 to June 2024 for all ED presentations, urology referrals, urology clinic visits, and urologic or interventional radiology interventions (cystoscopy, ureteral stent placement, nephrostomy tube insertions, ureteroscopy [URS], or shockwave lithotripsy [SWL]). All medical and imaging encounters in our province of approximately 5 million people are captured in our universal electronic medical record.

Ethical approval

This study protocol was approved by the University of Alberta Research Ethics Office Health Research Ethics Board—Health Panel (Pro00091664).

Outcomes

The primary outcome was the rate of urologic intervention for a SAUS (≤5 mm). Secondary outcomes included patient-reported stone-free and pain-free rates, initial patient disposition from the SAUS protocol, as well as long-term resource utilization, including emergency and hospital visits, urology clinic visits, and urologic intervention.

Statistical analysis

Mean values and standard deviations were reported for continuous variables and categorical variables were reported as frequencies (%). Initially, univariate logistic regression analysis was performed and the variables that were determined to be significant in the univariate analysis were considered in the multivariate logistic regression analysis. Survival analyses for re-presentation free and intervention free survival were conducted using Cox’s proportional hazards regression. SPSS version 29 (IBM Corp. Released 2023. IBM SPSS (Statistics for Windows, Version 29.0.2.0 Armonk, NY: IBM Corp) was used for all statistical analysis. A p-value of <0.05 was used for statistical significance and all hypothesis tests were based on two-sided tests. STROBE guidelines were adhered to for our study.⁷

Results

In total, 209 consecutive patients were enrolled in our virtual SAUS protocol. Patient demographics and stone characteristics are summarized in Table 1. The cohort predominantly consisted of men (n = 144, 69%), with a mean age of 48.7 years. The mean stone size was 3.8 mm (standard deviation 1.1). CT scan was the primary diagnostic modality (n = 194, 93%). Stones on initial referral imaging were predominantly positioned in the patient’s distal ureter (n = 143, 69%). The median follow-up period was 5.4 years (interquartile range [IQR] 5.2–5.9).

Table 1.

Patient Demographics and Stone Characteristics

	n = 209
Age, mean (SD)	48.7 (15.4)
Gender, men (%)	144 (69)
Stone size, mean (SD)	3.8 (1.1)
Stone location (%)
Proximal	42 (20)
Mid	23 (11)
Distal	143 (69)
Presence of nonobstructing renal stones on imaging (%)	35 (17)
Initial imaging modality (%)
CT	194 (93)
KUB Xray	3 (1)
US	12 (6)
Stone laterality (%)
Left	107 (51)
Right	102 (49)
Follow-up in years, median (IQR)	5.4 (5.2–5.9)

IQR = interquartile range; SD = standard deviation.

Of the 110 patients who were able to avoid an ASC appointment, 73 (35%) opted for follow-up with their PCP alone, 28 (13%) were scheduled for a nonurgent ESC appointment to review stone prevention, and 9 (4%) refused all follow-up (Fig. 2). Patients who avoided an ASC appointment were discharged from urologic care because of a presumption of stone passage (negative US and symptom-free), and only two (2%) patients necessitated delayed intervention for their ureteral stone at 2.7 months and 19.9 months, respectively.

FIG. 2.

Initial disposition from SAUS protocol (fu = follow-up).

Ninety-eight patients (47%) attended an ASC appointment with a urologist and one patient was referred directly for cystoscopy because of concerns of a concomitant bladder mass on follow-up ultrasound (Fig. 2). Of the patients who attended an ASC or cystoscopy appointment, 24 (24%) underwent urologic intervention for their small ureteral stone, with 5 (5%) undergoing SWL and 19 (19%) undergoing URS. Of the remaining 75 patients (75%) seen by a urologist in ASC, 2 (2%) necessitated delayed urologic intervention with URS for their ureteral stone, at 11.1 and 15.3 months, respectively, after presumed spontaneous stone passage.

Stone size (odds ratio [OR] 1.63, 95% confidence interval [CI]: 1.08–2.44, p = 0.02) and the presence of additional renal stones (OR 2.84, 95% CI: 1.14–7.08, p = 0.03) were the only significant predictors of patients who necessitated intervention for their small ureteral stone in the multiple logistic regression analysis.

Protocol efficiency

The mean time from initial ED presentation to endourologist triage was 1.5 days. Follow-up imaging was performed at a mean of 19.2 days post-ED visit. The initial nurse case manager patient encounter occurred at a mean of 20.5 days after initial referral to evaluate ultrasound results and review patient symptoms. Patients deemed to necessitate urologist evaluation were seen at a mean of 28.4 days from their initial referral.

Clinical outcomes

One hundred and sixty patients (77%) on follow-up RBUS demonstrated complete resolution of hydronephrosis and no evidence of ureteral stones, indicating radiographical confirmation of stone passage. At the time of nurse case manager follow-up after US, 140 (74%) of patients reported being symptom-free (sensitivity 82%, specificity 55%). Among the patients with persistent symptoms, 27 (55%) had normal ultrasounds. When asked if patients believed they had passed their stone, 71 (38%) of patients believed they had seen their stone pass, the majority of which 67 (94%) had ultrasound findings consistent with this. Self-reported stone passage had a 45% sensitivity and 88% specificity within this cohort.

Long term follow-up

Patients (n = 209) enrolled in SAUS were followed for a median of 5.4 years (IQR 5.2–5.9). Over the follow-up period, most patients did not re-present to the ED, their PCP, or their urologist with renal colic (n = 140, 67%, Fig. 3). Sixty-nine patients after SAUS protocol discharge re-presented to the hospital, clinic or the urology office, with only six (3%) presenting with symptoms related to their initial small ureteral stone. Of the remaining 63 patients, 16 (8%) experienced symptoms unrelated to nephrolithiasis with negative imaging at the time of re-presentation, 26 (12%) presented with symptoms related to a stone seen in the kidney on initial SAUS imaging, and 21 (10%) presented with symptoms related to newly formed stone that was not seen on initial SAUS imaging. Only 21 (10%) patients who had been enrolled and subsequently discharged from the SAUS protocol underwent stone intervention (URS or SWL) over the 5-year follow-up period (Fig. 4).

FIG. 3.

Kaplan–Meier presentation-free survival after SAUS protocol.

FIG. 4.

Kaplan–Meier intervention-free survival after SAUS protocol.

In the Cox’s proportional hazard regression analysis of re-presentation, there were no significant predictors (Table 2). Similarly, in the Cox’s proportional hazard regression analysis of intervention, only age was found to be a statistically significant predictor of intervention (hazard ratio 1.03, 95% CI: 1.00–1.06, p = 0.04) (Table 3).

Table 2.

Cox’s Hazard Proportional Regression Analysis of Re-Presentation

Variable	Univariate analysis
Variable	HR (95% CI)	p Value
Age (years)	1.00 (0.98–1.01)	0.69
Sex (men vs women)	0.92 (0.56–1.53)	0.76
Stone size (mm)	0.91 (0.73–1.14)	0.42
Presence of Renal Stone at initial imaging	1.15 (0.63–2.09)	0.66
Stone Location
Proximal	1.00 (reference)	1.00 (reference)
Middle	0.61 (0.26–1.44)	0.26
Distal	0.64 (0.37–1.09)	0.10

CI = confidence interval; HR = hazard ratio.

Table 3.

Cox’s Proportional Hazard Regression Analysis of Intervention

Variable	Univariate analysis		Multivariate analysis
Variable	HR (95% CI)	p Value	HR (95% CI)	p Value
Age (years)	1.03 (1.00–1.06)	0.04	1.03 (1.00–1.06)	0.04
Sex (men vs women)	1.06 (0.67–1.67)	0.80
Stone size (mm)	1.05 (0.70–1.58)	0.82
Presence of renal stone at initial imaging	1.51 (0.55–4.12)	0.42
Stone location
Proximal	1.00 (reference)	1.00 (reference)
Middle	0.27 (0.03–2.18)	0.22
Distal	0.54 (0.22–1.36)	0.19

Discussion

The results of this study demonstrate the effectiveness and efficiency of a SAUS protocol in virtually managing patients with small ureteral stones ≤5 mm. Our SAUS protocol effectively diverted 53% of patient referrals initially bound for an urgent urologist clinic visit, directly resulting in 110 additional patient clinic spots. Of the 99 patients who went on to an ASC visit, only 24 necessitated urologic intervention (URS or SWL) for their ureteral stone. Of the 110 patients who did not attend ASC, 108 were successfully discharged and did not require urologic intervention for their acute stone episode, showcasing that our SAUS protocol was effective in diverting patients who would never necessitate urologic intervention.

Long-term follow-up revealed that most patients (67%) remained free from symptomatic nephrolithiasis and did not re-present electively or urgently over the 5-year follow-up period after their initial stone episodes. Importantly, 90% of patients referred with ≤5 mm stones did not undergo any urologic intervention (SWL or URS) within the 5.4 year follow-up period. This underscores the protocol’s success in managing small ureteral stones conservatively, minimizing the need for surgical intervention. Overall, the SAUS protocol has proven to be an effective, efficient, and safe approach for managing SAUSs, with favorable short-term and long-term outcomes, providing a valuable template for urology groups.

We found that the rate of spontaneous stone passage was independent of the stone’s position within the ureter. This contrasts with the data presented in a systematic review of conservative stone management outcomes by Yallappa et al., which found that 49% of proximal stones, 58% of mid stones, and 68% of distal stones (compared with 71.5% proximal, 70% mid, and 75% distal in our sample) passed spontaneously within a similar period.⁵ Furthermore, the idea that a period of conservative management may allow for the passage of most small ureteral stones is not novel and is supported in the literature. The systematic review by Yallappa et al. found that there was a 75% spontaneous stone passage rate for stones <5 mm within 29 days, which is comparable with our rate of 77% total stone passage in 28 days.⁵ Our data therefore corroborates the notion that a period of conservative management allows for the passage of most ureteral stones ≤5 mm and symptom resolution and abides by international guidelines.^8

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The degree to which clinicians should rely on patient-reported outcomes as a measure of stone-free state was not assessed until recently. A publication from our center by McLarty et al. assessed the accuracy of patient-reported outcomes in predicting spontaneous stone passage and found that cessation of pain had a sensitivity of 79.7% and a specificity of 55.8%, compared with our analysis of symptom resolution having a sensitivity of 82% and a specificity of 55%.⁶ In addition, they reported patient-reported stone passage as being 59.3% sensitive and 87.0% specific, compared with our results of 45% sensitivity and 88% specificity. This underscores the importance of imaging tests as a complementary tool to subjective symptom evaluation for the development of a SAUS protocol.

Litwin and Saigal have shown costs associated with the treatment of kidney stones to be over $10 billion per year, based on data from 2006.³ Any innovations that result in reduced clinic, imaging, ED visits or interventions, therefore, play an important role in the reduction of direct costs, while maintaining safe and effective patient management. In addition, a study by Saigal et al. assessed the direct and indirect costs of nephrolithiasis in working-aged adults in the year 2000 and found that 30% of individuals missed work because of the disease, which resulted in a total of 19 hours of lost work time per individual per instance of nephrolithiasis.¹² However, they found that if the patient’s only contact with the health care system was an ambulatory clinic encounter, the missed work time decreased to 5.1 hours. While it is beyond the limitations of this study, the SAUS protocol might have the ability to reduce both direct and indirect costs associated with urolithiasis by avoiding 53% of urology consultations as well as unnecessary interventions.

Our study’s retrospective design may introduce bias related to data collection and patient follow-up, potentially affecting the accuracy and completeness of the reported outcomes, including the usage of medical expulsive therapy. A prospective study evaluating the SAUS protocol is planned, incorporating quality-of-life assessments and an analysis of resource utilization. The follow-up period, while comprehensive at a median of 5.4 years, may miss long-term complications or recurrences beyond this timeframe. Notably, however, our follow-up data are supported by our provincial-wide electronic health care system that captures all imaging, ED presentations, and surgical procedures, which enhances the validity of our findings. To our knowledge, only two patients moved provinces and were lost to follow-up.

Conclusion

The SAUS protocol, designed for obstructing ureteral stones ≤5 mm, successfully redirected 53% of patients from an urgent urology clinic visit, with only 13% of small ureteral stones necessitating urologic intervention. Long-term outcomes support the use of our protocol, with 90% of patients remaining free from urologic intervention over a median follow-up period of 5.4 years.

Footnotes

Authors’ Contributions

T.S., D.B., T.W., and S.D.: Conception and design. C.B., P.A., N.D., and M.M.: Acquisition of data. P.A., A.S., T.S., S.D., and N.D.: Analysis and interpretation of data. C.B., P.A., N.D., T.S., and S.D.: Drafting of article. D.B., T.W., S.D., T.S., A.S., P.A., and N.D.: Critical revision of the article for important intellectual content. A.S., P.A., M.M., and C.B.: Statistical analysis. T.S., S.D., T.W., and D.B.: Administrative, technical, or material support. T.S. and S.D.: Supervision. All authors have read and agreed to the published version of the article.

Author Disclosure Statement

Dr. Nicholas Dean is a consultant for Olympus Medical. The remaining authors have nothing to disclose.

Funding Information

No funding was received for this article.

Abbreviations Used

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