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The New Zealand Medical Journal

 Journal of the New Zealand Medical Association, 19-June-2009, Vol 122 No 1297

Renal stone disease in Christchurch, New Zealand. Part 2: a community study on the burden of renal stone disease
Peter J Davidson, Ian G Sheerin, Chris Frampton
Abstract
Aim To quantify the annual burden of a 12-month cohort of newly diagnosed renal stones in the defined community of Christchurch, New Zealand, and to assess this burden by stone size and position.
Method In this prospective study of stone burden, patients in the Christchurch region of New Zealand with newly diagnosed renal stones maintained a weekly diary for a 12-month period to record the utilisation of health services and financial and social costs to families and partners. Patient records were matched with diagnostic and clinical information to provide a comprehensive database. The economic costs of the various services were estimated.
Results From November 2001 to November 2002, 422 newly diagnosed renal stones were detected—an annual incidence of 105 per 100,000 population. The annual mean cost of these stones was NZ$4274 per person in the first 12 months. The greatest costs were those for emergency visits, hospitalisations and for operative procedures (23.8%, 22.7%, and 21.8% of total financial burden respectively). Patient workdays lost accounted for 10.9% of total costs. Ureteric stones caused greater social burden than kidney stones. Costs were influenced by stone location and size, being significantly higher for ureteric stones and for larger stones.
Conclusions: Renal stone disease places a considerable burden on the community. The main burdens were related to health service costs, with personal and pharmaceutical costs representing only a small component. The financial burden to society is estimated at $450,000 per 100,000 population ($NZ in 2001/02).

Renal stone disease creates a burden on the community not only through the direct costs of medical care and lost income, but also through the social cost of lost opportunity. The prevalence of renal stone disease is increasing, as is the cost of looking after patients with stones.1,2
Approximately 15% of men and 6% of women will be diagnosed with a renal stone at some time during their lives,2 and while some stones do not require medical intervention, the majority of people will avail themselves of medical services at some time for their stone disease.
Improved information on the societal costs of renal stone disease and a better understanding of how those costs are generated would allow for better planning of stone management. Treatment of nephrolithiasis has been demonstrated to be influenced by both the location and the size of kidney stones.2–4 Therefore, it is important to investigate the influence of stone size and location on costs and on the need for medical intervention.
While some studies have considered the financial burden of various stone treatments,4,5 and others the cost-effectiveness of different interventions,4,6,7 they generally do not provide details on non-medical stone burden. The total community burden of stone disease has not been well studied.
The burden of urolithiasis in the United States was analysed in the Urologic Diseases In America Project,1,8 which utilised a combination of a number of large data bases to estimate medical visits, intervention rates, and both the direct medical and indirect costs for urinary stone disease. They found that the total cost of urolithiasis is increasing, despite a shift from inpatient to outpatient treatment and the development of less invasive treatments. Renal stones were also associated with substantial lost work time.
The objective of this study is to quantify the full community burden of a 12-month period of newly diagnosed renal stones. It aims to do this by identifying all newly diagnosed stones in the community and following each stone in detail over that 12-month period. Further, the study aims to quantify the burden by both stone size and position.

Methods

In this prospective study, the patient population included all patients with a radiologically confirmed new diagnosis of renal and ureteric stones in the Christchurch region between November 2001 and November 2002. Patients were eligible for enrolment if they resided in either Christchurch City or the surrounding rural areas encompassed by the Waimakariri, Hurunui, Banks Peninsula or Selwyn Districts.
The seven radiological facilities servicing this area all used the same COMRAD package for radiological reporting. A query was designed to search for the keywords “stone”, “stones”, “calculus” and “calculi”. A daily list of all X-ray reports containing these keywords were scanned by research nurses and those containing reference to calculi or stones in either the ureter or kidney were identified.
Patients were then contacted on the next business day by the research nurses and, if this was the first time the stone had been diagnosed, asked to participate in the research. Stone data collected included size, location, and multiplicity.
Those signing consent had demographic data collected which included ethnicity, occupation, salary, address, gender, and age. Further information was collected on stone presentation, family history, and past history of urolithiasis. Participants filled out a weekly diary documenting time off work for both them and their partner, lost social opportunity, extra social support, visits to outpatients, after hours services, emergency, general practitioners, specialists and “other” practitioners, admissions to hospital, procedural interventions, X-rays, tests, medications and “any other financial impact.”
Patients were followed until either the stone had passed, or been removed, or they had been on the study for 12 months and still had their stone. Patient diaries were complemented by telephone follow-up which was verified by checking medical records and telephone calls to medical practitioners.
Costs of health services were estimated using a micro-costing approach in which detailed cost estimates were made of the services utilised by patients. Costs were valued in 2001/02 New Zealand dollars. A societal perspective was assumed, in which all costs associated with renal stones were estimated, including health service costs, and costs to private individuals.
In New Zealand, the majority of hospital and specialist services are funded through a system of taxation and public hospitals. The public hospital costs of hospitalisations, emergency room visits, radiology, and laboratory investigations were valued using actual costs provided by the Decision Support Unit of the Canterbury District Health Board (CDHB), the public provider in the study area. These costings are based on a patient allocation of true costs derived from the various cost centres involved in providing care to that patient.
For those patients who received private hospital treatment, the relevant costs were the actual costs charged by the private provider. As 97% of the costs of hospital interventions were incurred in the local non-profit public hospital, the vast majority of the costs were actual costs. So in these results, profit margins which may be included in private hospital charges were not a significant factor.
Pharmaceuticals were valued at the prices paid by the Pharmaceutical Management Agency of New Zealand. In New Zealand there are co-payments for pharmaceuticals, with the government covering the majority of the drug costs. Participants reported on the out-of-pocket costs of fees they had paid themselves for health services, pharmaceuticals, and visits to medical practitioners. The societal costs of lost production were estimated using the actual incomes of the participants, together with the reported hours of lost work.
Lost earnings for paid work of retired people, part time workers and people working from their own homes were included. Foregone social activities were also recorded for all participants, although no economic cost was assigned to them, following the recommendations of Brouwer, Rutten, Koopmanschap.9 Similarly, no monetary value was assigned for lost leisure time or lost unpaid work as conventional recommendations are that they should be treated as aspects of quality of life, rather than as “lost production” (ibid).
Statistical analyses were conducted using SPSS (v13.0) software. Patient characteristics were compared between consenting and non-consenting patients using Chi-squared tests and independent t-test as appropriate. Outcome data, including visits, costs, and days lost were compared between stone position and stone size groups using Chi-squared and Kruskal Wallis non-parametric ANOVAs depending on the form of the outcome variable. A p value <0.05 was taken to indicate statistical significance.

Results:

422 new stones were diagnosed over 12 months in a population of 400,250, giving an incidence of 105 newly diagnosed stones per 100,000 people. 280 patients agreed to enter the study; 74 failed to complete a year of diaries. Of these 4 were lost to follow up, 70 had their diaries completed by the research nurses by phone contact with the participant and these phone contacts were backed up by review of their medical records (public hospital, private and general practitioner).
The majority of these patients stopped filling their diaries as they had no further problems from their stones over the study period. Of the 142 that did not agree to participate, 47 gave consent to access their medical records, but for the purposes of this study are considered as non-participants. The 280 patients who agreed to be in the study were slightly younger and more likely to have ureteric stones that these non-participants (Table 1)
Table 1. Comparison between those presenting with stones who participated in the study and those “not in study”
Variables
In study
Not in study
P value
Age (Mean, years)
Gender (% female)
Stone size (Median, mm)
Stone location (% kidney)
Single vs multiple stones (% single)
49 (sd=14)
30.4
3 (range: 1–50)
28.9
75.4
51 (sd=20)
34.5
4 (range: 1–22)
45.1
77.5
0.18
0.39
0.40
0.001
0.63
The total financial burden of stone disease for this cohort of 280 patients is estimated at $1.197 million (Table 2). Costs of emergency visits were the largest health service costs (23.8%), followed by those for hospital bed days (22.7%), operative procedures (21.8%), and X-rays (10.5%). Costs of lost work days also comprised 10.9% of the total burden. Individually, the average cost of a newly diagnosed stone over a 12 month period was $4274.
Table 2. Financial burden to society of stone disease
Costs of:
Financial burden (N=280)
(in $NZ)
% of total financial burden
N
Burden
Mean cost per person
Diagnostic tests
X-rays
Pharmaceuticals
GP visits
Emergency visits
Specialist visits
Hospital bed days
Operations
Non-operative procedures
Work days lost
Partner work days lost
Other expenses
Total financial burden
Total burden per person
655
896
na
340
268
273
416
118
28
921
174
15
na
23,103
125,540
5,513
20,011
284,370
39,830
271,411
261,088
8587
130,373
20,058
6,713
1,196,597
83
448
20
71
1,016
142
969
932
31
466
72
24

4274
1.9
10.5
0.5
1.7
23.8
3.3
22.7
21.8
0.7
10.9
1.7
0.6
100
Notes: Costs are in 2001/02 NZ dollars. Percentages do not add to 100 because of rounding.
The social burden of stone disease was expressed in terms of missed social opportunities, missed days off work, and work days missed by the supporting partner. 39.6% of the 280 participants reported missing social events as a result of their stone disease over the study period. 53.9% of participants missed days off work and a further 27.1% of partners missed days off work.
Stone position had a significant effect on many of the indicators of stone burden (Table 3). The most common positions were the kidney (38.2%) and in the lower ureter (40.4%). Ureteric stones were more likely to result in emergency, after hours and outpatient visits (p<0.01). Renal stones resulted in significantly more specialist visits (p=0.002) and upper ureteric stones in a significantly greater number of admissions, and operative procedures (p<0.001).
Larger stone size was more likely to result in specialist visits in either the public hospital outpatients or in private practice (Table 4) (p<0.001). They were also more likely to result in admissions to hospital and procedures, both operative and nonoperative (p<0.001). Stone size did not have a significant influence on numbers of emergency department visits or after hours visits. Hence, stone size is a significant indicator of the utilisation of hospital admissions and surgical intervention.
Table 3. Percent reporting different types of medical contact by stone position
Variables
All stones
(N=280)
(%)
Kidney

(N=107)
(%)
Upper ureter
(N=31)
(%)
Middle ureter
(N=29)
(%)
Lower ureter
(N=113)
(%)
P value*
(Chi-squared test)
GP Visits
Emergency visits
After Hrs visits
Outpatient visits
Private specialist visits
Admissions
Operations
Nonoperative procedures
55.0
73.9
21.8
43.6
13.6
49.3
22.1
6.4
52.3
44.9
14.0
34.6
23.4
41.1
26.2
6.5
54.8
100
16.1
67.7
9.7
80.6
48.4
12.9
62.1
93.1
41.4
55.2
6.9
44.8
24.1
3.4
55.8
89.4
25.7
42.5
7.1
49.6
10.6
5.3
0.835
<0.001
0.010
0.010
0.002
0.002
<0.001
0.419
*P value indicates statistical significance for stone position.
Table 4. Percent reporting different types of medical contact by stone size
Variables
All stones
Stone size


(N=280)
<5 mm
(N=174)
(%)
5–9 mm
(N=84)
(%)
>9 mm
(N=22)
(%)
P value*
(Chi-Square test)
GP Visits
Emergency visits
After hours visits
Outpatient visits
Private specialist visits
Admissions
Operations
Nonoperative procedures
55.0
73.9
21.8
43.6
13.6
49.6
22.1
6.4
50.0
80.5
24.1
35.1
7.5
42.5
7.5
3.4
64.3
65.5
20.2
56.0
22.6
57.1
38.1
8.3
59.1
54.5
9.1
63.6
27.3
77.3
77.3
22.7
0.017
0.467
0.336
<0.001
<0.001
<0.001
<0.001
<0.001
*P value indicates statistical significance for stone size groups (<5 mm, 5–9 mm, and >9 mm).
The burden to society as valued by total costs per person was significantly greater for patients with ureteric stones (Table 5; significant at p<0.001). Ureteric stones were also associated with significantly higher mean per patient costs of operative procedures, bed days, emergency visits (p<0.001), outpatient visits (p=0.01), X-rays, and lost work days (p<0.05). There was no significant difference for drug costs.
Costs per person also tended to be significantly higher for people with larger stones (Table 6). Mean costs per person were significantly greater in larger stones for total costs, costs of procedures, outpatient visits (p<0.001), X-rays, and drugs (p<0.01).
Stone size did not significantly affect mean costs for emergency visits or lost work days.
Table 5. Types of costs ($NZ per person) of stone disease by stone position
Types of costs
(per person)
All participants
(N= 280)

mean (range)
Kidney

(N=107)
mean
Upper ureter
(N=31)
mean
Middle ureter
(N=29)
mean
Lower ureter
(N=113)
mean
P value*
(Kruskal-Wallis test)
Total burden
Procedure cost
Bed day cost
ED cost
X-ray cost
Cost work days lost
Drugs cost
Outpatient cost
4274 (84–3,241)
932 (0–18,902)
969 (0–18,664)
998 (0–5,635)
448 (52 –1,478)
466 (0–5,615)
20 (0–174)
119 (0–432)
4142
1386
762
648
430
458
23
101
8152
1874
2872
1582
577
603
23
185
4044
739
836
1152
457
403
20
149
3393
294
678
1130
428
451
15
110
<0.001
<0.001
<0.001
<0.001
0.018
0.046
0.467
0.010
*P value indicates statistical significance for stone position (in kidney, upper, middle, or lower ureter).
Table 6. Types of costs ($NZ per person) of stone disease by stone size
Types of costs
(per person):
All participants
(N=280)
mean cost & (range)
<5 mm
(N=174)
5–9mm
(N=84)
>9 mm
(N=22)
P value*
(Kruskal-Wallis test)
Total burden
Procedure cost
Bed day cost
ED cost
X-ray cost
Cost work days lost
Drugs cost
Outpatient cost
4274 (84–33,241)
932 (0–18,902)
969 (0–18,664)
998 (0–5,635)
448 (52–1,478)
466 (0–15,615)
20 (0–174)
119 (0–432)
3000
219
623
995
403
407
14
93
5485
1446
1469
1023
485
498
27
153
9719
4613
1798
934
667
811
36
192
<0.001
<0.001
0.008
0.284
0.002
0.481
0 .002
<0.001
*P value indicates statistical significance for stone size.
The relative costs of stones in an individual (considering stone location and size) are shown in Table 7. Large upper ureteric stones were the most expensive and small renal stones the lowest cost.
Table 7. Mean costs ($NZ per person) of stones by their size and location
Location
<5 mm
$ mean cost
5 to 9 mm
$ mean cost
>9 mm
$ mean cost
Kidney
Upper ureter
Mid ureter
Lower ureter
2312
5277
2580
3138
4033
9783
6247
4833
9577
10658
8384
No stones
Note: Differences were statistically significant at p<0.01, using analysis of variance.
Social burden was also assessed according to stone position and size. The percentage of participants who missed days of work was significantly related to stone position (Table 8). People with stones in the lower ureter reported lost work days more frequently, but individuals with upper ureteric stones tended to lose more days off work for each stone, thus costing more for lost work days. Days of work missed by supporting partners were reported in 27% of cases, and this was also significantly related to stone position.
Table 8. Percent reporting types of social burden by stone position
Variables
All stones
Stone position
P-value*
(Chi-squared test)

(N=280)
(%)
Kidney
N=107)
(%)
Upper ureter
(N=31)
(%)
Middle ureter
(N=29)
(%)
Lower ureter
(N=113)
(%)
Missed social event
39.6
35.5
39.7
34.5
45.1
0.693
Missed days of work
53.9
45.8
64.5
48.3
60.2
0.044
Partner support missed days
27.1
15.0
41.9
10.3
38.9
<0.001
*P value indicates statistical significance for stone position.
Missed social events were also reported by 39.6%. These types of social burden did not vary significantly by stone size (Table 9).
Table 9. Percent reporting types of social burden by stone size
Variables
All stones
Stone size
P value*
(Chi-squared test)

(N=280)
<5 mm
(N=174)
(%)
5–9 mm
(N=84)
(%)
>9 mm
(N=22)
(%)
Missed social event
Missed days of work
Partner support missed days
39.6
53.9
27.1
37.4
55.7
26.4
40.5
47.6
29.8
54.5
63.6
22.7
0.220
0.304
0.744
*P value indicates statistical significance for stone size.
The potential confounding influence of gender and age were investigated. Analysis of the data found that both stone size and position were important for all patients and the results did not vary significantly by age or gender.

Discussion

It is difficult to compare health costs between countries. Parker et al showed that in the USA the cost of stone treatment by ESWL was greater than by ureteroscopy.4 In Taiwan, Ying-Huej Lee et al showed the opposite, with ureteroscopic treatment costing more.10
Lotan et al showed that not only did the ratios of cost between these two treatments differ between the countries studied, but the total costs for each procedure varied greatly between countries, as did the cost of stone prevention.11
Such variation is a product of not just variations in prevalence, incidence and outcomes of treatment, but more importantly is highly sensitive to the differing cost drivers in the various countries. Therefore it is important for each country to assess the costs associated with diseases such as renal stone disease in their own country.
This study accurately defines the burden of renal stone disease in a New Zealand community of 400,250 people An incidence was documented of 105 newly diagnosed stones per 100,000 population.
280 out of 422 people with newly diagnosed stones consented to participate in this study If it is assumed that the costs were similar for non-participants, then the total annual financial burden in this community of kidney stone disease would be NZ$1.804 million, or NZ$450,000 per 100,000 people. If this were to be extrapolated to the whole New Zealand population, then it could be assumed that the financial burden of renal stone disease would be greater than 18 million dollars in 2002.
There have been many different ways of trying to estimate the financial burden of renal stone disease. The simplest approach is to simply assess the direct costs of equipment and consumables for a particular procedure.12 This neglects the real costs of bed days, theatre time and the other costs associated with any particular treatment. Others have included these costs, but only as regards different treatment options.4,10
This approach does not cost non-treated stones. Other studies have tried to approach the costing of renal stone disease by complex decision analysis models11, which require the use of a number of assumptions. These assumptions are at risk of inaccuracies, which can compound through such a model, resulting in a flawed outcome.
The most comprehensive attempts to define the community financial burden of stone disease are the studies of Saigal et al8 and Pearle et al. 1 They attempt to define the burden of stone disease by extrapolating down from large community based databases, which give a good indication of overall cost, but have little ability to assess the detail of the cost drivers. The approach taken in the current study is unique in that it defines the burden of renal stone disease by building up actual costs of each new stone diagnosed, in both a defined and captive community.
In this study, only 280 out of the potential study population of 422 consented to be involved. Therefore a potential weakness of this approach could be that the costs might be different between those that consented to be on the study when compared with those that did not. The only significant difference between the two groups was that there were proportionately fewer kidney stones in the study group, and as these stones were less expensive, there could potentially be a slight over representation of the financial burden for the whole group.
Of those not consenting to participate in the study, the overwhelming reasons for withholding consent were that they were either “too busy” or “couldn’t be bothered”. It is possible that this group would have a higher percentage of working men and women, thus causing a possible under representation of the cost of lost work days and overall financial burden in the study population. Any differences in overall and individual financial burden are likely to be small, and the relative costs by stone position and size are unlikely to be substantially altered as a result of the non participants.
A further potential weakness of the approach used in this study is that of the onus on the study participant to identify all events and costs associated with their stones. As each patient was phoned weekly to confirm the events on the diary (and to enquire about events in the 70 participants who ceased filling out their weekly diary themselves), this is unlikely. Furthermore, cross correlation with GP and hospital records minimised erroneous reporting, thus making this an unlikely source of error.
In a US study, stone size has previously not been shown to have an impact on cost4, when stones were divided between those less than and those greater than 1 cm. This study by Parker et al, however only compared the cost of stone treatment by either ureteroscopy or ESWL. In the current study, all costs associated with the stone are included, which explains the finding of a significant difference in financial burden by stone size. In addition, the position of a stone has a significant financial and social impact.
Large stones in the upper ureter are the most expensive at $10,658 per stone. When the drivers of this cost are explored, it is found that these stones have recurrent emergency visits and admissions and most eventually end up with a surgical removal. Stones located in the ureter are often painful and therefore more likely to require surgical intervention.
Data such as this can allow for the modification of stone management such that these stones are dealt with as expeditiously as possible, to avoid these recurrent presentation to health services. Furthermore, the cost data detail presented in this study can form the basis for the design of future randomised trials of differing stone management strategies.
In addition to the importance of stone size and position, this study shows that the main burden of costs are health service costs, particularly those of emergency department visits, hospitalisations and medical procedures.
Costs falling on private individuals were a relatively small percentage of the overall burden, but were still significant at approximately 13% of the total burden. The costs of diagnostic investigations were also important, comprising approximately 12% of total costs. Perhaps surprisingly, the costs of pharmaceuticals were relatively low at less than 1% of the total burden.
This study also looks at the social burdens of renal stone disease. While there is a financial burden, there is also a social burden to patients and their families. Saigel et al8 found that one third of their patients missed work due to their kidney stones. Over half of our patients (53.9%) missed between them a total of 921 days and 27.1% of their partners missed a total of 174 days of work.
Thus in a 12-month period there were 1095 days of lost productivity. Ureteric stones were more likely to cause this lost productivity. The authors had anticipated that stones would cause considerable social disruption in terms of lost social events, as these stones are often extremely painful. Surprisingly, only 39.6% missed social events and this was independent of both stone size and location.
As this percentage is less than the percentage missing days of work, it could be concluded that either participants were more reluctant to miss social events, or alternatively there were fewer opportunities to miss social events than work days.

Conclusion

The annual incidence of newly diagnosed renal stones was 105 per 100,000 population. A total annual financial burden of kidney stone disease in this community was estimated to be NZ$1.804 million, or NZ$450,000 per 100,000 people. The greatest costs were those of emergency department visits, hospital bed days and operative procedures.
Costs varied significantly with the main influences being stone location and stone size. Larger stones and those located in the upper ureter were associated with significantly higher costs.
Competing interests: None known.
Author information: Peter J Davidson, Urologist, Curt Medical Trials Trust, Christchurch; Ian G Sheerin, Health Economist, Christchurch School of Medicine, University of Otago, Christchurch; Chris Frampton, Biostatistician, Christchurch School of Medicine, University of Otago, Christchurch
Acknowledgements: The authors acknowledge the diligence of the participants of the study, the hard work of the research nurses at CURT Medical Trials Trust, the help and co-operation of the staff of the Christchurch Radiology Department, Christchurch Medical Imaging and Canterbury Radiology Group, and finally, the financial support of Mobile Medical Technology in the form of an unrestricted grant.
Correspondence: Dr Peter Davidson, CURT Medical Trials Trust, St Georges Medical Centre, 249 Papanui Rd, Christchurch, New Zealand. Fax: +64(0)3 3556368; email: research@urology.co.nz
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