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| Journal of the New Zealand Medical Association,
19-June-2009, Vol 122 No 1297
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Renal stone disease in Christchurch, New Zealand.
Part 1: presentation and epidemiology
Peter J Davidson, Ian G Sheerin, Chris Frampton
Stone disease in the ureter and kidney (renal stone disease)
is a common and increasing disease of affluent
civilisations.1 There is little data on renal
stone disease in New Zealand, and no epidemiological studies in a New Zealand
population were found in a comprehensive literature search.
Studies in other Western countries indicate that
approximately 15% of men and 6% of women will be diagnosed with a renal stone at
some time during their lives.2 Renal stones are
associated with considerable pain, suffering, and costs to health services.
Therefore, published information is of interest to health professionals involved
in the diagnosis and treatment of urolithiasis, as well as to those who plan and
manage health services.
This study presents for the first time information about the
presentation and epidemiology of renal stone disease in a defined and complete
New Zealand population. It was undertaken to document the modes of presentation
and epidemiology of radiologically diagnosed renal stone disease over a 1-year
period in the region of Christchurch, New Zealand.
MethodThe 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 by the research nurses and, if this was
the first time the stone had been diagnosed, asked to participate in the
research.
In all new presenters, data was available from the
radiological report on gender, age, stone size, stone position, and stone
multiplicity.
Patients who signed consent (N=280) were interviewed .
An additional 47 patients declined to be interviewed, but gave consent for
project investigators to collect information from their medical records. In
these 327 participants, information was gathered on demographics, ethnicity,
occupation, income, stone presentation, family history, and past history of
urolithiasis. There were another 95 people who presented with stones during the
study period, but who declined to participate. These non-participants were
counted in the “new radiological stone diagnoses”, but we were not
able to obtain key information on them to include them in the statistical
analysis in this paper.
Data was analysed using Statistical Package for the
Social Sciences (SPSS, Version 13). Pearson’s, Chi-squared, and t-tests
were used to test for statistical significance among presentation variables.
Results422 new radiological stone diagnoses were made in a
population of 400,250 people, giving an incidence of 105 per 100,000 per annum.
280 patients agreed to enter the study. Of the 142 that did not agree to
participate, 47 gave consent to access their medical records, thus giving 327
stone presenters in whom access to medical records was possible. The reasons for
declining enrolment in the trial are set out in Table 1.
Table 1. Reasons for declining
enrollment
The 280 patients who agreed to be in the study were less
likely to have stones in the kidney than the non-participants, but in all other
aspects the two groups were similar (Table 2).
Table 2. Comparison between those presenting
with stones who participated in the trial and those “not on
trial”
Std – standard deviation
Of the 422 patients with a new radiological stone diagnosis,
24 % had multiple stones at presentation, with 4.6% having 3 or more stones. 38
% of these stones were in the kidneys and 62 % in the ureters.
The breakdown of the stones by size and location is shown in
Table 3 for all people diagnosed with renal stones (N=422) . Roughly half the
stones in the kidney were 5 mm or greater in diameter, and the proportion of
larger stones decreased as the stones were detected further down the ureter,
with only 20% of lower ureteric stones being 5 mm or greater. This difference
was statistically significant (p<0.001).
Table 3. Stone position by size
Note: Percentages may not add to 100
due to rounding; Chi-squared = 35.798, p<0.001, 3 df.
There were some seasonal variations in presentations
although these were not statistically significant. The season with the highest
number of presentations was autumn (31%), followed by winter (26%), summer
(26%), and spring (17%). The season of presentation did not differ significantly
by age, gender, stone size, location, or whether patients presented with pain,
haematuria, or incidentally.
Of those who presented with a new stone during the study
period, 70% were male and 30% were female. There was no significant difference
in the mean age of men (51 years) and the mean age of women (47 years) at
presentation.
Figure 1 shows that the age distribution of people
presenting with renal stones is very different from that for the general
Canterbury population. The majority (two-thirds) of stone presenters were aged
between 30 years and 60 years. People aged less than 30 years were relatively
uncommon (8%) as were people aged over 70 years (12%).
Figure 1. People presenting with new stones by
age group.
 Note: Age
statistics for the Canterbury population were from the 2001 New Zealand
census.
Ninety percent of stone presenters were of European ethnic
origin. Only 3% were Māori and 1.5% were from Pacific Islands. The ethnic
distribution found in this study is similar to that for the general Canterbury
population, although Māori are slightly under-represented among people who
were diagnosed with renal stones.
Sixty percent of patients were in paid employment and a
breakdown of their occupations is shown in Figure 2. The proportion of study
participants in managerial and professional work (39%) was similar to that for
the general workforce in Canterbury in 2001 (Figure 2). The proportion of stone
presenters in trades or machine operating jobs (27%) was comparatively larger
than for the general workforce in Canterbury, which in 2001 had 18% in these
occupations.
Participants in service and sales jobs (18%) were
proportionally fewer than in the general Canterbury workforce (27%).
Of those patients who were not in paid employment (N=129),
19% were housewives or on the domestic purposes benefit (DPB), 9% were students,
and 39% were retired or unemployed. The other 33% who were not in paid
employment did not declare their reason.
Of the 327 who agreed to either participate in the study, or
to make available information from their medical records, 33% had a personal
history of previous renal stone disease and 20% had a family history of stone
disease. There were no statistically significant differences in personal or
family history by age, gender, stone position, size, or symptoms on
presentation.
The vast majority (80%) of participating patients with renal
and ureteric stones presented with pain; 15% were discovered incidentally, 4%
with haematuria, and 1% with infection. Stone position and size influenced the
presenting symptoms (Table 4); 94% of stones in the ureter presented with
pain.
Figure 2. Occupations of people presenting with
stones compared with the general Canterbury population of people aged 15 years
and over in paid employment
 Note: Canterbury population statistics
obtained from the 2001 New Zealand Census.
Although 61% of stones in the kidney also presented with
pain, 39% of them presented with other symptoms (p<0.001)(Table 4). Twelve
out of the 13 patients presenting with painless haematuria had stones in the
kidney, while 84% of the patients whose stones were discovered incidentally were
in the kidney.
Table 4. Influence of stone location and size
on presenting symptoms
 Note: percentages may not add to 100
due to rounding.
There was a statistically significant difference in
presenting symptoms according to size of renal stone (p<0.001) (Table 4).
While pain was the most common presentation in participants with both large and
small stones, other non-painful presentations were more common in stones of 5 mm
or over (32%). The majority of people with larger stones and with symptoms other
than pain had their stones located in the kidney.
DiscussionPublished studies have shown a clear rise in the incidence
and prevalence of kidney stone disease in the Western world over the last
century.1 Current estimates of prevalence rates
in European and North American countries are reported between 5% and 18.5%.
Taiwan and Japan have prevalence rates of 9.8 and 10%
respectively.3,5 Incidences vary greatly with
Trinchieri describing a range from 56 to 326 per 100,000 population per
year.1
A major cause for such a range in incidences is the
variation in the populations studied. Many studies measure incidence of
hospitalisation or acute presentation, while others use physician or patient
self reporting, or limit their study population by gender or age. All of these
studies have the weakness of possibly misrepresenting the true incidence in
stone disease in these communities. A strength of this present study is that all
stones are radiologically confirmed, and that all radiologically confirmed
stones are captured. Thus the incidence of 105 new renal stone presentations per
100,000 population per annum in the Christchurch region is likely to be an
accurate estimate.
Most studies of seasonal variation in the diagnosis of renal
stones show in increase in summer and autumn.5
In stone formers, a decrease in urine volume, sodium, and pH, with
correspondingly higher supersaturations of calcium oxylate and uric acid has
been demonstrated during the summer months.6 We
did not find an increase in the summer months, which may be due to the large
number of asymptomatic stones in this series, as the other studies have been in
populations presenting with acute colic.
The ratio of men to women diagnosed with a stone was 2.3:1.
This is consistent with the findings in all studies of the epidemiology of stone
disease, in that a greater number of men than women are diagnosed with renal
stone disease. Ratios vary from 1.4:1 in
Iceland7 to 6.3:1 in
Korea.8 There is a suggestion in the USA that
the gap is closing, with Lieske and colleagues observing a change in the ratio
from 3:1 to 1.3:1 over a period of 30 years in Rochester,
Minnesota.9
Ethnicity has been shown to be relevant in an American
population with the highest prevalence being in Caucasians, with Hispanics and
Asians next and blacks least likely to develop renal stone
disease.10,11
We found no difference in the incidence of stone
presentation by ethnicity, but this may have been confounded by the overwhelming
majority of our population being Caucasian. Anecdotally it is felt that the
Māori and Polynesian populations in New Zealand have a higher incidence of
stone disease. This study was not able to confirm this, and it is possible that
these populations may have worse stone burden which is more difficult to treat,
giving the impression of a higher incidence. Further studies in a population
containing a higher number of Māori and Pacific Island peoples would be
needed to clarify this further.
The finding of an over representation of trades and machine
operator jobs among the stone presenters is consistent with other studies. Serio
and Fraioli showed a higher prevalence in non educated than educated stone
formers,12 while hot occupations and outdoor
work have also been associated with increased stone
risk.13,14
While trade and machine operating jobs are likely to include
all three noted risk factors, it is surprising that in this study stones were
not also more likely in agricultural and labouring jobs, which also share these
risk factors and through them an increased risk of chronic
dehydration.13
Within our study population 20% reported a family history of
stone disease, and this lies within the range of 8.1% to 31% recorded in the
literature.7,8,12,15 Stone formers have
previously been observed to have a more frequent family history of stone disease
than non stone formers.16
Although not assessed in this study, it has been suggested
previously that stone disease is more common with a maternal history than
paternal3 , and when parents have stone disease
when compared to siblings.12
Pain was the most common presenting symptom in stones of
less than 5 mm diameter and in ureteric stones, which is to be expected, as
small stones are more likely to enter the ureter, resulting in painful renal
colic. The large number of incidentally discovered stones in the kidney reflects
the radiologically diagnosed population, many of whom were clinically evaluated
for reasons other than stone-related symptoms.
This study was not designed to assess other epidemiological
factors previously noted to be significant in the formation of renal stones,
including obesity, diet, beverage intake, geographic location, chronic disease,
and stress. Neither does the study allow for multifactorial analysis of
stone-forming factors.
A weakness of the study is that further epidemiological
information was not able to be collected on all stone presenters, with only 66%
agreeing to information on ethnicity, occupation, and salary—and 77%
having data on symptoms at presentation, past medical history, and family
history of stone disease. As the predominant reason for not enrolling in the
trial was that the stone presenters were too busy, there could potentially be a
bias in the data against working men and women.
ConclusionKidney stone disease is a significant health condition that
affects men more than women, and people of predominantly working ages.
It’s incidence is increasing. There were some occupational differences in
stone incidence that may be explained by lifestyle factors including
dehydration. Both personal and family history of previous stone disease appears
to be a significant risk factor. Pain was the most common presenting symptom,
and the majority of these patients had stones located in the ureter. Renal
stones presented more commonly with other symptoms, particularly haematuria
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
References:
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