A retrospective study on the management of ureteric stones following presentation to the emergency department in the University Hospitals Sussex Trust East from November 2020 to November 2021

Abstract

Objective:

To ascertain which patient demographic, clinical and stone-specific factors were significant when predicting intervention for ureteric stones and determine the proportion of patients with smaller, more distally located stones requiring intervention to establish whether follow-up imaging was indicated to confirm stone passage.

Subjects/patients and methods:

This is a retrospective review of 227 patients presenting with ureteric stones on non-contrast computerised tomography (NCCT) between November 2020 and November 2021. Eleven different clinical, demographic and imaging-related factors were recorded, and multivariate logistical regression was used to determine which factors were significant when predicting intervention.

Results:

A total of 53 patients (23.3%) underwent some form of intervention with only stone size (p < 0.001) and stone location (p < 0.001) significant in predicting treatment. Only 4.17% of patients with a ⩽ 4 mm distally located stone required intervention. These patients either had raised inflammatory markers or significant pain.

Conclusion:

Given that 95.83% of patients with ⩽ 4 mm distal ureteric calculi passed their stone spontaneously, a patient-initiated follow-up (PIFU) could be implemented to replace a follow-up NCCT. Based on this dataset, the application of PIFU could have prevented additional radiation exposure of 1.5–3 mSv/patient and excess financial cost of approximately £7000 to services.

Level of Evidence:

Level 3

Keywords

Ureteric stone PIFU ureter ureteric colic urolithiasis NCCT

Introduction

Urolithiasis is common in the United Kingdom with a lifetime incidence of around 6% in women and 12% in men.^1,2 This led to an estimated cost of £190 to £324 million in 2010 in England creating a significant financial burden on the NHS.³ Predicting which ureteric calculi will require intervention is challenging. The National Institute for Health and Care Excellence (NICE)⁴ and the European Association of Urology (EAU)⁵ guidelines cite indications as persistent pain refractory to analgesia, persistent obstruction and renal insufficiency. Other guidance refers to the location and size with stones < 5 mm in the distal ureter often managed conservatively due to the high likelihood of spontaneous passage.⁵ Clinical factors suggested to predict ureteric calculi outcomes include infection markers, kidney function and imaging findings.^6–9 An ambiguous aspect of management is the requirement for follow-up imaging. Repeat imaging to ensure spontaneous stone passage (SSP) of small stones is not mentioned by either the EAU or NICE within their guidelines questioning the necessity.^5,10

Current protocols within this hospital trust are such that patients with ureteric stones ⩾ 5 mm are first offered extracorporeal shockwave lithotripsy (ESWL). Patients with 4 mm stones are offered ESWL if the stone can be visualised on X-ray and is proximally located. Ureteroscopy (URS) was offered for larger stones or those stones untreatable by ESWL. Previously, an emergency URS list was available for patients showing signs of infection; however, this service was not available during the COVID-19 pandemic, during which this data collection took place; therefore, these patients instead had stents inserted. Patients discharged from the emergency department (ED) with < 4 mm calculi and no signs of infection had a follow-up non-contrast computerised tomography (NCCT) scan booked 4–6 weeks after the presentation to ensure stone passage or guide further management.

Aims

To ascertain which patient demographic, clinical and stone-specific factors were significant when predicting whether the intervention was required to remove the patient’s ureteric stone. The secondary aim is to determine the proportion of patients in this cohort requiring intervention presenting with smaller and more distally located stones to subsequently establish whether follow-up imaging was needed to confirm SSP.

Methods

Study design

This is a retrospective study of patients with ureteric stones presenting to the ED at the University Hospital Sussex (UHS) Trust East with urolithiasis between November 2020 and November 2021. During this time, Brighton and Sussex University Hospitals and Western Sussex Hospitals Trusts merged although urology services remained split, hence the clarification of UHS East. As per NICE⁴ and EAU⁵ guidelines, all patients with suspected stones had an NCCT scan to confirm the presence, location and size. Results of the scan together with other relevant clinical findings were detailed in the ‘Renal Colic Referral Form’ also encompassing patients presenting with ureteric colic. Investigations included history from the patient, urinalysis, urea and electrolytes (U&Es) and full blood count (FBC). Using a database with the submitted forms, we identified patients with confirmed ureteric calculi on NCCT.

Definition of variables

NCCT scans were reported by the trust uroradiologists and included the number, location within the ureter and size in mm of the stones. Sizes were categorised into ⩽4, >4 to ⩽5, >5 to ⩽6, >6 to ⩽7, and >7 mm and chosen due to the range of sizes in the dataset and the current trust protocol in offering intervention. The smallest stone size category (⩽4 mm) was used for comparison in logistical regression analysis. Location was divided into subsections of the ureter; upper, mid and distal. Upper included both the pelviureteric junction (PUJ) and proximal ureter. Distal included both the vesicoureteric junction (VUJ) and distal ureter as reported on NCCT. The distal was used for comparison as stones located here had the highest likelihood of SSP.

Other information included patient demographics: age, gender and index of multiple deprivation. This index was obtained by entering the patient’s postcodes into the English Indices of Deprivation 2019 postcode lookup.¹¹ Clinical findings included white blood cell (WBC) count, C-reactive protein (CRP), estimated glomerular filtration rate (eGFR) and whether the patient had a known history of stones. Raised WBC count was defined as being over 10 × 10⁹/L, raised CRP being over 5 mg/L and lowered eGFR being under 60 mL/min which are the reference ranges present in the hospital trust.

Outcome measure

No intervention was defined as no evidence of the stone on follow-up NCCT 4–6 weeks after presentation. Forms of intervention used included: ESWL, stenting and definitive URS. If patients had been booked for a procedure which had not yet occurred at the time of collecting data, they were categorised as needing intervention.

Inclusion/exclusion

The total number of patients with renal colic referral forms in the timeframe was 424. Reasons for exclusion included no presence of ureteric calculi on imaging, having multiple ureteric calculi present upon imaging, having incomplete data available and those lost to follow-up due to not attending follow-up NCCT after two invitations from the urology team, or seeking care elsewhere. Subsequently, 197 patients were excluded leaving 227 patients in the final analysis.

Statistical analysis

Binomial logistical regression was performed using IBM SPSS Statistics Version 27. Univariate logistical regression was performed on each individual variable to ascertain significance followed by multivariate analysis on those that were statistically significant. A confidence interval of 95% was used with p < 0.05 considered to indicate statistical significance in all tests.

Results

Of the 227 patients included, 174 (76.7%) had SSP and 53 (23.3%) underwent some form of intervention. Notably, 163 (71.8%) of the patients were male and 64 (28.2%) were female with the average age being 47.2 years. 69 (30.4%) of the patients had previously had ureteric or renal stones. Most patients lived in areas that were in the least deprived quintile (29.1%) with the fewest living in areas that were in the most deprived quintile (11.5%).

A total of 122 (53.7%) patients had a raised WBC count, 45 (19.8%) had a raised CRP and 35 (15.4%) had eGFR below 60. Notably, 101 (44.5%) patients had a stone in the left ureter and 126 (55.5%) in the right. Most patients had stones located in the distal ureter (154, 67.8%) and least had stones in the mid ureter (21, 9.3%). The average stone size was 4.66 mm with the majority (122, 53.7%) of stones being in the smallest size category (⩽4 mm) with 52 (22.9%) being >4 to ⩽5 mm, 21 (9.3%) >5 to ⩽6 mm, 18 (7.9%) >6 to ⩽7 mm and 14 (6.2%) >7 mm.

Totally, 53 patients underwent some form of intervention of which 37 patients had ESWL, 18 required a stent and 21 underwent a definitive URS. Some patients required multiple interventions and some procedures had been booked but not performed. After the initial assessment, 19 patients were admitted for immediate treatment or observation before being discharged. It is important to appreciate the previously mentioned lack of emergency URS list due to the COVID-19 pandemic, and therefore the number of stents placed is higher than in non-COVID times. Table 1 summarises the variables recorded, separated by patients who underwent a form of intervention and those who did not.

Table 1.

Summary of variables split by those requiring intervention and those not.

Variable	No intervention	Intervention
Gender
Male	129 (74.1%)	34 (64.2%)
Female	45 (25.9%)	19 (35.8%)
Age	46.81	48.57
Depravition index
Quintile 1	21 (12.1%)	5 (9.4%)
2	27 (15.5%)	9 (17%)
3	31 (17.8%)	13 (24.5%)
4	45 (25.9%)	10 (18.9%)
5	50 (28.7%)	16 (30.2%)
Raised WBC (>10×10 ⁹ /L)
Yes (y)	96 (55.2%)	27 (50.9%)
No (N)	78 (44.8%)	26 (49.1%)
Raised CRP (>5 mg/L)
Y	29 (16.7%)	16 (30.2%)
N	145 (83.3%)	37 (69.8%)
Lowered eGFR (<60 mL/min)
Y	26 (14.9%)	9 (17%)
N	148 (85.1%)	44 (83%)
Previous stones
Y	48 (27.6%)	21 (39.6%)
N	126 (72.4%)	32 (60.4%)
Admitted
Y	13 (7.5%)	12 (22.6%)
N	161 (92.5%)	41 (77.4%)
Side of stone
Right	97 (55.7%)	29 (54.7%)
Left	77 (44.3%)	24 (45.3%)
Ureteric stone size
⩽4 mm	113 (64.9%)	9 (17%)
>4 to ⩽5 mm	41 (23.6%)	11 (20.8%)
>5 to ⩽6 mm	12 (6.9%)	9 (17%)
>6 to ⩽7 mm	7 (4%)	11 (20.8%)
>7 mm	1 (0.6%)	13 (24.5%)
Stone location
Upper	24 (13.8%)	28 (52.8%)
Mid	10 (5.7%)	11 (20.8%)
Distal	140 (80.5%)	14 (26.4%)

Logistical regression

After performing univariate analysis, the significant variables in predicting whether intervention was needed included stone size in mm in every size category (compared with the smallest stones) (p ⩽ 0.001), stone location within the ureter (compared with the distal part) (p ⩽ 0.001) and a raised CRP (2.16 (1.06–4.39), p = 0.03). The significant variables were combined into the multivariate analysis. Results from the univariate and multivariate analyses are shown in Table 2.

Table 2.

Univariate and multivariate logistical regression.

Variable	Univariate		Multivariate
Variable	Odds ratio	p-value	Adjusted odds ratio	p-value
Gender
Male	1	—
Female	1.60 (0.83–3.09)	0.16
Age	1.01 (0.99–1.03)	0.43
Depravition index		0.72
Quintile 1	0.74 (0.24–2.29)	0.61
2	1.04 (0.41–2.67)	0.93
3	1.31 (0.56–3.09)	0.54
4	0.69 (0.29–1.69)	0.42
5	1	—
WBC
Normal range	1	—
Raised (>10×10⁹/L)	0.78 (0.42–1.45)	0.44
CRP
Normal range	1	—	1	—
Raised (>5 mg/L)	2.16 (1.06–4.39)	0.03	2.14 (0.79–5.80)	0.14
eGFR under 60 mL/min
Normal (>60 mL/min)	1	—
Low (<60 mL/min)	1.16 (0.51–2.67)	0.72
Previous stones
N	1	—
Y	1.723 (0.91–3.28)	0.097
Ureteric stone size		<0.001		<0.001
⩽4 mm	1	—	1	—
>4 to ⩽5 mm	3.37 (1.30–8.72)	0.012	3.00 (1.06–8.55)	0.039
>5 to ⩽6 mm	9.42 (3.14–28.26)	<0.001	6.48 (1.89–22.15)	0.003
>6 to ⩽7 mm	19.73 (6.15–63.30)	<0.001	11.97 (3.24–44.16)	<0.001
>7 mm	163.22 (19.12–1393.20)	<0.001	96.32 (10.14–914.89)	<0.001
Stone location		<0.001		<0.001
Upper	11.67 (5.38–25.30)	<0.001	8.16 (3.26–20.40)	<0.001
Mid	11 (3.98–30.43)	<0.001	8.24 (2.48–27.38)	<0.001
Distal ureter	1	—	1	—

After multivariate analysis, having a raised CRP (OR 2.14 (0.79–5.80), p = 0.14) was no longer significant. Stone location (p ⩽ 0.001) and size (p ⩽ 0.001) remained significant in every category. When compared with the smallest stone category (⩾4 mm), there was a step wise increase in OR as sizes increased from >4 to ⩽5 mm (OR = 3.00 (1.06–8.55), p = 0.039) to >7 mm (96.32 (10.14–914.89), p ⩽ 0.001). When compared with the distal ureter, stones in both the upper (8.16 (3.26–20.40), p ⩽ 0.001) and mid (8.16 (3.26–20.40), p ⩽ 0.001) sections of the ureter were more likely to require intervention.

Based on the multivariate analysis, we created a separate results table (Table 3) of patients requiring intervention with only the variables that remained significant which were the stone location and size.

Table 3.

Percentage of patients requiring intervention depending on size and location of stone.

	Distal ureter	Mid ureter	Upper ureter
⩽4 mm	4.17%	16.67%	20%
>4 to ⩽5 mm	10.5%	40%	55.56%
>5 to ⩽6 mm	10%	80%	66.67%
>6 to ⩽7 mm	42.9%	66.67%	75%
>7 mm	66.67%	100%	100%

In Table 3, the percentage of patients requiring intervention increases as both stone size increases and the location becomes more proximal. When looking at patients with stones ⩽ 4 mm in the distal segment of the ureter 95.83% had SSP. Excluding those admitted to the ward and just including outpatients, this increased to 97.8%.

Discussion

Results from our analysis of 227 patients echoed findings from other studies^8,9,12-16 with only stone size and location remaining significant in multivariate analysis when predicting intervention. When analysing rates of SSP, our study demonstrated 90.9% of all sized stones located in the distal ureter passed without intervention and 92.6% of ⩽4 mm stones in all locations. This is higher than Yallappa et al.¹⁶ reported in their analysis of 6600 patients with 68% of distal stones passing spontaneously and 75% of stones <5 mm in any location although this study had a larger proportion of smaller and more distally located stones in comparison. Jendeberg et al.¹³ found 80% of 4 mm stones in the upper urinary tract passed spontaneously with Miller and Kane¹⁷ reporting 95% of ureteric stones 2–4 mm passing spontaneously demonstrating similar results to our study regarding higher SSP rates of smaller and more distally located ureteric stones.

Clinical factors significant in the univariate analysis included a raised CRP. However, this became insignificant when analysed in the multivariate. Multiple studies included CRP as a variable with conflicting results; Jendeberg et al.¹³ found it to be insignificant; however, Mohammad et al.¹⁸ and Park et al.⁶ suggest that a raised CRP could be an indication for intervention. Another clinical factor with conflicting evidence is WBC count with Sfoungaristos et al.¹⁵ emphasising it as the most significant predictor of SSP theorising that a moveable ureteric stone would produce a greater inflammatory response. WBC count was not significant in our univariate analysis which echoes findings in previously mentioned studies.^13,19 Although significance of CRP and WBC count as predictors is contradictory, their function as markers of inflammation could still be considered indication for intervention.

Other clinical variables suggested to predict the outcome of ureteric stones include those evidenced on imaging. Özcan et al.⁸ found the presence of hydronephrosis to be a predictor of SSP for stones 4–10 mm. Alevizopoulos et al.⁹ theorise the extent of hydronephrosis was related to ureteric stone size and therefore the likelihood of intervention. Yoshida et al.²⁰ described hydroureter as a potential indication for intervention in ureteric stones ⩽ 10 mm due to the inflammatory changes associated with stone impaction. Unfortunately, these CT findings were not included in our study due to expert analysis being unavailable within the time frame.

Given the high percentages of SSP for smaller stones, the requirement for follow-up imaging is debatable. Neither EAU or NICE guidelines^4,5 state follow-up imaging is required to confirm SSP with the American Urological Association (AUA) concluding that there is a lack of evidence relating to ureteral stone follow-up.²¹ The safety of excluding follow-up imaging must be considered given the risk of silent obstruction of the kidney. One study²² in America found of the 1.1% asymptomatic stones over a 12-year period, 25% had a degree of hydronephrosis although the mean stone size was 10 mm. They also concluded that severe cases of nephrolithiasis are almost always related to symptoms. A further study by Noh et al.²³ concluded that asymptomatic ureteric stones could cause irreversible kidney damage; however, of these silent stones, only 14% were in the lower ureter with an average size of 11.4 mm. Marchini et al.²⁴ concluded that there was resolution of hydronephrosis and restored kidney function following stone removal in patients with silent stones. These studies had significantly larger average stone sizes than in our study; therefore, the risk in smaller stones may be harder to predict.

During the SUSPEND randomised controlled trial exploring medical expulsive therapy in around 1100 patients, SSP was defined as requiring no further intervention at 4 weeks with no follow-up imaging protocolised.²⁵ Notably, 95.83% of patients in our study with ⩽ 4 mm distally located stones had SSP with 3 of the 4 patients requiring intervention presenting with raised inflammatory markers and the other presenting with severe pain as reported by the admitting clinician. Excluding those admitted, rates of SSP for outpatients increased to 97.8%. NCCT scans emit 1.5–3 mSv/scan and cost £71 to £81 based on 2019 estimates, not including human resource costs.^26,27 Therefore, those patients with SSP of ⩽4 mm distally located stones had potentially unnecessary radiation exposure of 1.5–3 mSv/patient with a collective cost of £6,532–£7,452 to the NHS. A patient-initiated follow-up (PIFU) could be nominated for these patients with no clinical indication for admission or immediate treatment, discharging them after initial presentation due to the high likelihood of SSP. Consideration must be given to certain patient groups such as women attempting to conceive and those in professions such as HGV drivers and pilots. These patients would be excluded from the PIFU and have a confirmatory CT. A PIFU can reduce burden on services while giving patients more agency in self-management of conditions.²⁸ The UHS East urology service have subsequently nominated a clinical nurse specialist to explore PIFU, for patients to contact if they still experience symptoms. This could prevent unnecessary radiation, minimise excess costs and reduce burden on the urology services in this trust.

Limitations of our study include not measuring those variables that could have been significant in predicting the need for intervention as evidenced in other studies such as hydronephrosis or hydroureter. There was no standardisation of CT scan analysis, although there were four dedicated consultant uroradiologists reporting most scans. This is particularly pertinent due to the specification of ⩽4 mm stones as they are more challenging to accurately report. Furthermore, our study included a larger proportion of smaller and more distally located stones in comparison with other similar studies which could bias results. There was a high number of patients lost to follow up which may be in part due to health anxiety around the pandemic. Strengths include the large sample size and following patients from initial presentation through the management of their ureteral calculi.

Conclusion

Ureteral calculi create a significant burden on healthcare services and knowing which patients to offer a timely intervention to is crucial to avoid complications. Based on this subset of 227 patients presenting to ED at UHS East trust with ureteric stones over a 1-year period, the only significant factors when predicting whether their stone will require intervention was stone size in mm and location within the ureter. Given just under 95% of all patients with stones ⩽ 4 mm distally located passed spontaneously, a follow-up NCCT after presentation, as is the current trust protocol, may not be required. Subsequently, a PIFU could be nominated with a clinical nurse specialist to provide a safety net for those few patients with small stones that may require intervention. This avoids both excess financial and human resource strain on services and additional radiation exposure to patients.

Footnotes

Conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship and/or publication of this article.

Ethical approval

Ethical approval was not sought for this article.

Informed consent

Informed consent was not sought for this article because all patient data were anonymised.

Guarantor

A.R.

Contributorship

A.R. and P.Z. researched literature and developed the study. A.R. was involved in data analysis with both P.Z. and A.S. providing relevance and applicability to clinical practice. A.R. wrote the first draft of the manuscript. All authors reviewed and edited the manuscript and approved the final version of the manuscript.

ORCID iD

Ava Rietdyk

References

Council IIA. Occupational risks for urolithiasis: IIAC information note, 2018, https://www.gov.uk/government/publications/occupational-risks-for-urolithiasis-iiac-information-note/occupational-risks-for-urolithiasis-iiac-information-note

Rukin

Siddiqui

Chedgy

ECP

, et al. Trends in upper tract stone disease in England: Evidence from the hospital episodes statistics database. Urol Int 2017; 98(4): 391–396.

Geraghty

Cook

Walker

, et al. Evaluation of the economic burden of kidney stone disease in the UK: A retrospective cohort study with a mean follow-up of 19 years. BJU Int 2020; 125(4): 586–594.

Renal and ureteric stones: Assessment and management, 2019, https://www.nice.org.uk/guidance/ng118/chapter/Recommendations#surgical-treatments-including-shockwave-lithotripsy

Skolarikos

Jung

Neisius , et al. EAU guidelines on uroliahiasis EAU guidelines. Netherlands EAU Guidelines Office, 2023, https://d56bochluxqnz.cloudfront.net/documents/full-guideline/EAU-Guidelines-on-Urolithiasis-2023.pdf.

Park

, et al. Relationship between spontaneous passage rates of ureteral stones less than 8 mm and serum C-reactive protein levels and neutrophil percentages. Korean J Urol 2013; 54(9): 615–618.

Sfoungaristos

Kavouras

Katafigiotis

, et al. Role of white blood cell and neutrophil counts in predicting spontaneous stone passage in patients with renal colic. BJU Int 2012; 110(8 Pt. B): E339–E345.

Özcan

Aydoğdu

Senocak

, et al. Predictive factors for spontaneous stone passage and the potential role of serum C-reactive protein in patients with 4 to 10 mm distal ureteral stones: A prospective clinical study. J Urol 2015; 194(4): 1009–1013.

Alevizopoulos

Zosimas

Piha

, et al. Managing small ureteral stones: A retrospective study on follow-up, clinical outcomes and cost-effectiveness of conservative management vs early surgery. Curr Urol 2016; 9(1): 36–43.

10.

NICE. Renal or ureteric colic – acute, 2020, https://cks.nice.org.uk/topics/renal-or-ureteric-colic-acute/

11.

Ministry of Housing, Communities and Local Government. English indices of deprivation 2019, https://imd-by-postcode.opendatacommunities.org/imd/2019.

12.

Choi

Yoo

Choi

, et al. Analysis of factors affecting spontaneous expulsion of ureteral stones that may predict unfavorable outcomes during watchful waiting periods: What is the influence of diabetes mellitus on the ureter. Korean J Urol 2015; 56(6): 455–460.

13.

Jendeberg

Geijer

Alshamari

, et al. Size matters: The width and location of a ureteral stone accurately predict the chance of spontaneous passage. Eur Radiol 2017; 27(11): 4775–4785.

14.

Modai

Avda

Shpunt

, et al. Prediction of surgical intervention for distal ureteral stones. J Endourol 2019; 33(9): 750–754.

15.

Sfoungaristos

Kavouras

Perimenis

. Predictors for spontaneous stone passage in patients with renal colic secondary to ureteral calculi. Int Urol Nephrol 2012; 44(1): 71–79.

16.

Yallappa

Amer

Jones

, et al. Natural history of conservatively managed ureteral stones: Analysis of 6600 patients. J Endourol 2018; 32(5): 371–379.

17.

Miller OF and Kane CJ. Time to stone passage for observed ureteral calculi: A guide for patient education. J Urol 1999; 162(3 Pt. 1): 688–690; discussion 690.

18.

Mohammad

Abbas

Hassan

, et al. Serum c-reactive protein as a predictive factor for spontaneous stone passage in patients with 4 to 8 mm distal ureteral stones. Int Surg J 2018; 5(4): 1195–1200.

19.

Shah

Gao

Peters

, et al. Factors associated with spontaneous stone passage in a contemporary cohort of patients presenting with acute ureteric colic: Results from the multi-centre cohort study evaluating the role of inflammatory markers in patients presenting with acute ureteric colic (MIMIC) study. BJU Int 2019; 124(3): 504–513.

20.

Yoshida

Inoue

Taguchi

, et al. Ureteral wall thickness as a significant factor in predicting spontaneous passage of ureteral stones of ⩽ 10 mm: A preliminary report. World J Urol 2019; 37(5): 913–919.

21.

Fulgham

Assimos

Pearle

, et al. Clinical effectiveness protocols for imaging in the management of ureteral calculous disease: AUA technology assessment. J Urol 2013; 189(4): 1203–1213.

22.

Wimpissinger

Türk

Kheyfets

, et al. The silence of the stones: Asymptomatic ureteral calculi. J Urol 2007; 178(4 Pt. 1): 1341–1344; discussion 1344.

23.

Noh

Pyun

Shim

, et al. A comparison between asymptomatic and symptomatic ureteral stones. Sci Rep 2023; 13: 2757.

24.

Marchini

Vicentini

Mazzucchi

, et al. Silent ureteral stones: Impact on kidney function–Can treatment of silent ureteral stones preserve kidney function? Urology 2012; 79(2): 304–308.

25.

Pickard

Starr

MacLennan

, et al. Medical expulsive therapy in adults with ureteric colic: A multicentre, randomised, placebo-controlled trial. Lancet 2015; 386(9991): 341–349.

26.

Brisbane

Bailey

Sorensen

. An overview of kidney stone imaging techniques. Nat Rev Urol 2016; 13(11): 654–662.

27.

NICE. StoneChecker for kidney stone evaluation, 2019, www.nice.org.uk/guidance/mib171

28.

NHS England. Patient initiated follow-up, 2022, https://www.england.nhs.uk/outpatient-transformation-programme/patient-initiated-follow-up-giving-patients-greater-control-over-their-hospital-follow-up-care/