Kidney stones and kidney function loss: A cohort study

ArticleinBMJ (online) 345(aug29 2):e5287 · August 2012with50 Reads
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Abstract

To investigate whether the presence of kidney stones increase the risk of end stage renal disease (ESRD) or other adverse renal outcomes. A registry cohort study using validated algorithms based on claims and facility utilisation data. Median follow-up of 11 years. Alberta, Canada, between 1997 and 2009. 3,089,194 adult patients without ESRD at baseline or a history of pyelonephritis. Of these, 1,954,836 had outpatient serum creatinine measurements and were included in analyses of chronic kidney disease and doubling of serum creatinine level. One or more kidney stones during follow-up. Incident ESRD, development of stage 3b-5 chronic kidney disease (estimated glomerular filtration rate <45 mL/min/1.73 m(2)), and sustained doubling of serum creatinine concentration from baseline. 23,706 (0.8%) patients had at least one kidney stone, 5333 (0.2%) developed ESRD, 68,525 (4%) developed stage 3b-5 chronic kidney disease, and 6581 (0.3%) experienced sustained doubling of serum creatinine. Overall, one or more stone episodes during follow-up was associated with increased risk of ESRD (adjusted hazard ratio 2.16 (95% CI 1.79 to 2.62)), new stage 3b-5 chronic kidney disease (hazard ratio 1.74 (1.61 to 1.88)), and doubling of serum creatinine (hazard ratio 1.94 (1.56 to 2.43)), all compared with those without kidney stones during follow-up. The excess risk of adverse outcomes associated with at least one episode of stones seemed greater in women than in men, and in people aged <50 years than in those aged ≥ 50. However, the risks of all three adverse outcomes in those with at least one episode of stones were significantly higher than in those without stones in both sexes and age strata. The absolute increase in the rate of adverse renal outcomes associated with stones was small: the unadjusted rate of ESRD was 2.48 per million person days in people with one or more episodes of stones versus 0.52 per million person days in people without stones. Even a single kidney stone episode during follow-up was associated with a significant increase in the likelihood of adverse renal outcomes including ESRD. However, the increases were small in absolute terms.

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Available from: R. Todd Alexander
Kidney stones and kidney function loss: a cohort study
OPEN ACCESS
R Todd Alexander assistant professor
1
, Brenda R Hemmelgarn associate professor
2
, Natasha
Wiebe research associate
1
, Aminu Bello research fellow
1
, Catherine Morgan assistant professor
1
,
Susan Samuel assistant professor
2
, Scott W Klarenbach associate professor
1
, Gary C Curhan
professor
3
, Marcello Tonelli professor
1
, for the Alberta Kidney Disease Network
1
7-129 Clinical Science Building, University of Alberta, 8440 112 Street, Edmonton, Alberta T6B 2G3, Canada;
2
University of Calgary, Calgary,
Canada;
3
Channing Laboratory, Harvard University, Boston, USA
Abstract
Objective To investigate whether the presence of kidney stones increase
the risk of end stage renal disease (ESRD) or other adverse renal
outcomes.
Design A registry cohort study using validated algorithms based on
claims and facility utilisation data. Median follow-up of 11 years.
Setting Alberta, Canada, between 1997 and 2009.
Participants 3 089 194 adult patients without ESRD at baseline or a
history of pyelonephritis. Of these, 1 954 836 had outpatient serum
creatinine measurements and were included in analyses of chronic
kidney disease and doubling of serum creatinine level.
Exposure One or more kidney stones during follow-up.
Main outcome measures Incident ESRD, development of stage 3b–5
chronic kidney disease (estimated glomerular filtration rate <45
mL/min/1.73 m
2
), and sustained doubling of serum creatinine
concentration from baseline.
Results 23 706 (0.8%) patients had at least one kidney stone, 5333
(0.2%) developed ESRD, 68 525 (4%) developed stage 3b–5 chronic
kidney disease, and 6581 (0.3%) experienced sustained doubling of
serum creatinine. Overall, one or more stone episodes during follow-up
was associated with increased risk of ESRD (adjusted hazard ratio 2.16
(95% CI 1.79 to 2.62)), new stage 3b–5 chronic kidney disease (hazard
ratio 1.74 (1.61 to 1.88)), and doubling of serum creatinine (hazard ratio
1.94 (1.56 to 2.43)), all compared with those without kidney stones during
follow-up. The excess risk of adverse outcomes associated with at least
one episode of stones seemed greater in women than in men, and in
people aged <50 years than in those aged ≥50. However, the risks of
all three adverse outcomes in those with at least one episode of stones
were significantly higher than in those without stones in both sexes and
age strata. The absolute increase in the rate of adverse renal outcomes
associated with stones was small: the unadjusted rate of ESRD was
2.48 per million person days in people with one or more episodes of
stones versus 0.52 per million person days in people without stones.
Conclusion Even a single kidney stone episode during follow-up was
associated with a significant increase in the likelihood of adverse renal
outcomes including ESRD. However, the increases were small in
absolute terms.
Introduction
End stage renal disease (ESRD), chronic kidney disease, and
kidney stones are common clinical problems with considerable
socioeconomic impact.
1-3
Patients with rare genetic disorders
that cause nephrolithiasis (such as primary hyperoxaluria and
cystinuria) may develop ESRD as a consequence of their stone
disease.
4-8
However, kidney stones are infrequently implicated
as the primary cause of ESRD (0.2–3.2% of all ESRD cases).
5 9 10
Limited evidence suggests an association between kidney stones
and the development of chronic kidney disease.
11-14
However,
whether kidney stones are a risk factor for the development of
ESRD is unclear.
13
Because kidney stones are common and potentially preventable,
an accurate assessment of their potential long term consequences
would be important to inform health interventions. We used a
large, population based cohort of people receiving care in a
universal healthcare system in Canada to study this issue. We
hypothesised that an episode of kidney stones would be
associated with excess risk of adverse renal outcomes, including
ESRD, development of clinically relevant chronic kidney disease
(stage 3b–5; defined by estimated glomerular filtration rate <45
mL/min/1.73 m
2
) or sustained doubling of serum creatinine
concentration from baseline.
Methods
Population and data sources
This study used the Alberta Kidney Disease Network database,
which incorporates data from Alberta Health and Wellness (the
provincial health ministry), the Northern and Southern Alberta
Correspondence to: M Tonelli mtonelli-admin@med.ualberta.ca
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Research
RESEARCH
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Renal Programs, and the clinical laboratories in Alberta.
15
The
database was used to assemble a cohort of adults aged ≥18 years
who resided in Alberta, Canada, between April 1997 and March
2009. All people registered with Alberta Health and Wellness
were eligible for inclusion. All Alberta residents are eligible for
insurance coverage by Alberta Health and Wellness, and >99%
participate in this coverage. We excluded patients with ESRD
(defined as documented estimated glomerular filtration rate <15
mL/min/1.73 m
2
, chronic dialysis, or prior kidney transplant)
at baseline. Because of the known relation between
pyelonephritis and kidney stones (and the potential for
pyelonephritis to cause kidney failure), we excluded patients
with pyelonephritis before or during follow-up. To identify
pyelonephritis we used the ICD-9 (international classification
of diseases, ninth revision) codes 590, 590.10, 590.00, 590.80,
590.2, 590.9, 590.80, and 590.3 and ICD-10 codes N10, N11.0,
N11.1, N11.8, N11.9, N12, N13.6, N15.1, N15.9, N16.0,
N28.83, N28.84, and N28.85. We followed patients from April
1997, their 18th birthday, or registration with Alberta Health
and Wellness (whichever was later) until March 2009.
Presentation with kidney stone episodes
We used physician claims, data on use of hospitalisation and
ambulatory care, and ICD-9 codes (592, 594, 274.11) and
ICD-10 codes (N20.0, N20.1, N20.2, N20.9, N21.0, N21.1,
N21.8, N21.9, N22.0, N22.8) to identify presentations of kidney
stones. The accuracy of these codes in defining a kidney stone
episode has been validated.
12
One or more of these codes in any
position for any inpatient or outpatient claim was taken to
represent an episode of kidney stones. We assumed that an
interval of a year or more between claims represented separate
kidney stone episodes; claims occurring within a year of each
other were classified as a result of a single stone episode.
16 17
Other covariates
Demographic variables included age (categorised as 18–49,
50–69, and ≥70 years), sex, Aboriginal (registered First Nations
or recognised Inuit), receipt of social assistance, and rural or
urban residence. We used validated algorithms to define the
Charlson comorbidities and hypertension
18
at baseline using
physician claims and data on use of hospitalisation and
ambulatory care. The Charlson score was based on the Deyo
classification
19
of the following comorbidities: cerebrovascular
disease, peripheral vascular disease, congestive heart failure,
cancer, chronic obstructive pulmonary disease, dementia,
diabetes with and without complications, AIDS/HIV, metastatic
solid tumour, myocardial infarction, mild liver disease, moderate
or severe liver disease, paralysis, peptic ulcer disease, and
rheumatic disease. We used physician claims and data on use
of hospitalisation and ambulatory care to assess for a history of
kidney stone at baseline (that is, at least three years before
follow-up) using the ICD codes above.
Clinical outcomes
The primary outcome was ESRD, defined as receipt of a kidney
transplant or initiation of chronic dialysis during follow-up, and
ascertained by data linkage to the Northern and Southern Alberta
Renal Programs. Using a subset of patients with data for serum
creatinine concentration, we followed patients from their first
available outpatient serum creatinine measurement (May 2002
or later) until March 2009. Patients with estimated glomerular
filtration rate <45 mL/min/1.73 m
2
at baseline were excluded
from these analyses. Kidney stones occurring on or before the
index date were counted as a prior kidney stone, and only events
occurring after the first kidney stone episode were included in
the analysis. Outcomes assessed in this subset of patients
included new stage 3b–5 chronic kidney disease (estimated
glomerular filtration rate <45 mL/min/1.73 m
2
) and sustained
doubling of serum creatinine concentration (a surrogate measure
for progressive kidney disease). Doubling of serum creatinine
was considered to have occurred at the time when a serum
creatinine value was found to be twice as high as the first
measurement during the study provided that all subsequent
values during follow-up remained at least twice as high as at
baseline.
20
Glomerular filtration rate was estimated with the
Chronic Kidney Disease Epidemiology Collaboration equation.
21
Statistical analyses
We did analyses with Stata/MP 11.2 (www.stata.com) and
reported baseline descriptive statistics as counts and percentages
or as medians and interquartile ranges, as appropriate. Absolute
rates were calculated by totalling the number of events and
dividing by the total follow-up time. These are presented as
events per 1 000 000 person days.
Using each participant as the unit of analysis, we estimated the
associations between first episode of kidney stone and outcomes
by using multivariable Cox proportional hazards models adjusted
for all variables presented in table 1. For new stage 3b–5
chronic kidney disease and sustained doubling of serum
creatinine outcomes, we additionally adjusted for baseline
estimated glomerular filtration rate. Time of origin was arbitrary
(April 1997 or later, as described above in “Population and data
sources”).
Kidney stone episodes were used to update exposure status
during follow-up—meaning that a person experiencing a single
stone episode during the course of follow-up would contribute
person time to the “no stone” hazard before the stone episode
(regardless of prior stone history) and person time to the “stone”
hazard after the stone episode. We explored the associations
between the outcomes and multiple episodes of stones in further
analyses. Tests for trend were performed by assigning 0, 1, or
2 for none, one, or multiple stone episodes, respectively.
We censored follow-up when a participant died, moved out of
the province, or reached the end of the study (31 March 2009).
We determined that the proportional hazard assumption was
satisfied by examining plots of the log-negative log of
within-group survivorship probabilities versus log time. The
threshold probability for statistical significance was set at 0.05.
Age and sex were explored as potential modifiers of the
association between kidney stones and clinical outcomes.
Results
Characteristics of study patients
There were 3 089 194 eligible patients without ESRD (or
estimated glomerular filtration rate <15 mL/min/1.73 m
2
) at
baseline (fig 1). Of these, 1 954 836 had outpatient serum
creatinine measurements and were included in analyses of new
stage 3b–5 chronic kidney disease and sustained doubling of
serum creatinine level from baseline. The characteristics of the
study patients with and without kidney stone episodes are shown
in table 1. Patients with kidney stones were older and more
likely to be men, to have had hypertension, and to have a history
of kidney stones.
During the median follow-up period of 11 years (range 1 day
to 12 years), 5333 (0.2%) registry patients developed ESRD,
200 790 (7%) died, and 229 556 (7%) moved outside Alberta.
In the subset of patients with serum creatinine data, the median
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follow-up period was four years (range 1 day to 7 years), and
in this period 68 525 (4%) patients developed stage 3b–5 chronic
kidney disease, 6581 (0.3%) experienced sustained doubling of
serum creatinine from baseline, 79 787 (4%) died, and 74 843
(4%) moved outside Alberta.
Relation between kidney stone episodes and
ESRD, stage 3b–5 chronic kidney disease, or
doubling of serum creatinine concentration
The adjusted risk of incident ESRD, our primary outcome, was
significantly higher in patients with one or more episodes of
kidney stones (hazard ratio 2.16 (95% confidence interval 1.79
to 2.62), table 2, fig 2). Results were similar in analyses that
did not adjust for prior kidney stones (hazard ratio 2.11 (1.77
to 2.52)) and in analyses that excluded participants with prior
kidney stones (hazard ratio 2.06 (1.67 to 2.55)). A significant
association between one or more episodes of kidney stones was
also observed for the adjusted risk of new stage 3b–5 chronic
kidney disease (hazard ratio 1.74 (1.61 to 1.88)) and sustained
doubling of serum creatinine concentration from baseline (1.94
(1.56 to 2.43)).
The absolute increase in the rate of adverse renal outcomes
associated with stones was small: the unadjusted rate of ESRD
was 2.48 per million person days in people with one or more
episodes of stones, compared with 0.52 per million person days
in people without stones. Corresponding unadjusted rates of
new stage 3b–5 chronic kidney disease and sustained doubling
of serum creatinine from baseline were 61.47 versus 25.53 and
7.69 versus 2.40 respectively.
The risk of adverse renal outcomes associated with kidney stones
seemed to increase with the number of stone episodes, since the
adjusted risk of ESRD and doubling of serum creatinine were
both greater in patients with multiple episodes of stones as
compared with those with a single episode or no stones (table
2).
Effect modification by age and sex
In analyses that separately evaluated the effect modification of
age and sex (table 3, fig 2), the adjusted risk of ESRD
associated with one or more episodes of stones (compared with
those without stones) seemed greater for women than men (P
value for interaction 0.003). Results were similar in the other
two adverse renal outcomes, although this interaction was of
borderline significance for new stage 3b–5 chronic kidney
disease (P=0.06). The risk of incident ESRD associated with
one or more stone episodes (versus no stones) was not
significantly higher in people aged <50 years than in those aged
≥50 (P=0.11), but the risk of the other two adverse renal
outcomes was significantly greater in those aged <50 than in
those who were older (both P≤0.01, table 3). Although the
magnitude of the association between stones and adverse
outcomes was greater for women than for men and for those
aged <50 years than for those aged ≥50, the risk of all three
outcomes in those with at least one episode of stones was
significantly higher than in those without stones in both sexes
and both age strata (table 3). The absolute increase in the rate
of ESRD was small for all age and sex subgroups (fig 2).
Results were similar in analyses that examined the risk of ESRD
associated with kidney stones in strata defined by the
intersection of age and sex (fig 2). Specifically, the magnitude
of the excess risk remained greater in female and younger
participants, and the risk of all three adverse renal outcomes
(data not shown) was significantly increased in the four mutually
exclusive groups formed by the intersection of age and sex.
Discussion
Kidney stones are a common and potentially preventable cause
of morbidity in the general population. Using a cohort of more
than three million people treated in a universal healthcare
system, we found that the risks of end stage renal disease
(ESRD) and of two other clinically relevant adverse renal
outcomes were all significantly higher in people with at least
one symptomatic kidney stone episode.
The excess risk of all three adverse renal outcomes that was
associated with stone episodes seemed to be greater in women
than in men and greater among younger people than in those
aged ≥50 years. The observed association between stones and
risk was independent of potential confounders (shown in table
1) and seemed to be magnified in people with more than one
episode of stones compared with those with a single episode.
These findings suggest that kidney stones are an important
potential contributor to the risk of ESRD and that patients with
prior kidney stones should be considered at increased risk for
adverse renal outcomes—especially younger women or those
with multiple symptomatic episodes.
Comparison with other studies
Consistent with our data, a recent prospective cohort study of
about 1.5 million people in the United Kingdom found that
kidney stones were a significant risk for ESRD in women but
not men.
14
The basis for this finding is unclear, but we speculate
that, although men are more likely to develop stones, they are
protected from obstructive complications due to differing
anatomy. The lack of a significant association between stones
and ESRD in men in the UK study
14
may have been due to the
smaller sample size and shorter period of follow-up. In our
study, the risk of adverse renal outcomes associated with a
kidney stone episode was more pronounced in younger
participants—perhaps because of the competing risk of death
(or the increased frequency of other risk factors for progressive
kidney function loss) in those who were older.
Consistent with our findings, Stankus et al found that a self
reported history of kidney stones was associated with a twofold
increased risk of ESRD among African-American patients.
11
Another study examining the impact of kidney stones on renal
outcomes found that kidney stones were associated with the
development of chronic kidney disease,
12
but it failed to establish
an association between kidney stones and ESRD—perhaps
because of its smaller sample size.
Potential mechanisms for the findings
What mechanisms link kidney stones to adverse renal outcomes?
People with rare monogenetic disorders that cause kidney stones
(such as primary hyperoxaluria and cystinuria) are at increased
risk for ESRD, apparently because of the renal damage caused
by stone formation.
5-7 9
In the absence of such unusual
conditions, and given the heterogeneous nature of kidney stones
and their formation, the link between stones and adverse renal
outcomes is likely multifactorial.
22
The association between
calcium kidney stones and progressive loss of kidney function
may be the direct result of progressive calcification within the
renal interstitium, and specifically at the tubular basement
membrane and around the ducts of Bellini.
22 23
Extension of such
calcification into the tubular lumen might cause more renal
damage, with potential for progressive scarring, chronic kidney
disease, and ultimately ESRD. Alternatively, crystallisation
within the tubular lumen itself may cause damage to the tubular
epithelium, and/or obstruction leading to progressive
scarring.
13 22 23
It is also possible that repeated episodes of urinary
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Page 3
tract obstruction associated with stones could contribute to
progressive loss of renal function. Finally, it is possible that
surgical or percutaneous treatment of stones (rather than the
stones themselves) accounts for the excess risk of kidney
function loss. However, since our data do not permit us to
address the mechanism linking kidney stones to adverse renal
outcomes, these speculations require confirmation in future
mechanistic studies.
Limitations
Our study is limited by the fact that people with kidney stones
were identified by their presentation to health services, meaning
that our findings do not apply to those who did not seek medical
care for a stone episode. Consequently we cannot comment on
the association between asymptomatic kidney stones and adverse
renal outcomes. Similarly, although we attempted to capture
discrete episodes of kidney stones, the algorithm we used
requires some assumptions, and some patients were therefore
probably misclassified with respect to their number of
presentations. Since we prospectively used claims and
hospitalisation data to assess the incidence of kidney stones
(rather than a history obtained at the time of dialysis initiation),
ascertainment bias due to more complete assessment of stones
among patients with ESRD is unlikely to have influenced our
findings. We were not able to determine the composition of the
kidney stones and thus cannot assess the specific risk associated
with different stone types. Although we adjusted for numerous
characteristics that differ by whether a participant had a kidney
stone episode (such as age, prior kidney stone, and other
comorbidity), the possibility for residual confounding remains.
Patients with stones may be more likely to have serum creatinine
concentration measured—and, therefore, we might be more
likely to detect a sustained doubling of serum creatinine or new
chronic kidney disease in this group. However, given that ESRD
is unlikely to remain undetected for long, the primary outcome
is unlikely to have been biased in this way. Finally, since the
dataset we used did not include genetic information, we cannot
assess how many of the patients in our study had a monogenic
disorder predisposing to stones. However, given the number of
ESRD events in our study, it seems unlikely that our findings
are driven by such rare conditions.
Conclusions
In conclusion, we found a graded association between episodes
of kidney stones and the risk of adverse renal outcomes,
including ESRD. Further research should be aimed at
determining the mechanisms explaining this association and
assessing the optimal way to prevent kidney stones in the general
population, especially young women.
Contributors: RTA conceived the study. RTA, NW, AB, and MT designed
the analysis plan. NW performed the statistical analyses. RTA, NW,
and MT wrote the first draft of the study. All authors contributed to the
design, interpretation of results, and critical revision of the article for
intellectually important content.
Funding: This work was supported by a team grant to the Interdisciplinary
Chronic Disease Collaboration from the Alberta Heritage Foundation
for Medical Research (AHFMR), the Kidney Foundation of Canada, and
by the University Hospital Foundation. RTA is supported by a
Clinician-Scientist award from the Canadian Institute of Health Research,
a KRESCENT New Investigator award, and an Alberta Innovates Health
Solutions Clinical Investigator Award. SS is supported by a KRESCENT
New Investigator award and a Canadian Child Health Clinician Scientist
Program Career Development award. GCC is supported by grant
DK070756 from the National Institutes of Health. MT is supported by
an AHFMR Population Health Scholar award and a Government of
Canada Research Chair in the optimal care of people with chronic kidney
disease.
Competing interests: All authors have completed the ICMJE uniform
disclosure form at ww.icmje.org/coi_disclosure.pdf (available on request
from the corresponding author) and declare: no financial relationships
with any organisations that might have an interest in the submitted work
in the previous three years; and no other relationships or activities that
could appear to have influenced the submitted work.
Ethical approval: Our protocol was approved by the University of Alberta
Health Research Ethics Board and the University of Calgary Conjoint
Health Research Ethics Board.
Data sharing: No additional data available.
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Accepted: 25 July 2012
Cite this as: BMJ 2012;345:e5287
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What is already known on this topic
The association between kidney stones and the risk of subsequent kidney failure is uncertain
What this study adds
This population based study found that one or more episodes of kidney stones during follow-up increases the risk of developing kidney
failure over a median period of 11 years
Tables
Table 1| Demographic and clinical characteristics of study patients with and without kidney stone episodes. Values are numbers (percentages)
of patients unless stated otherwise
Laboratory dataset†Registry dataset*
Characteristic
No stone
(n=1 943 227)
Stone(s)
(n=11 609)
No stone
(n=3 065 488)
Stone(s)
(n=23 706)
45.9 (34–57.6)51.6 (41.2–63.2)35.4 (23.2–48.6)46 (35.1–60.1)Median (IQR) age (years)
869 635 (44.8)7517 (64.8)1 537 388 (50.2)15 686 (66.2)Male
47 562 (2.4)222 (1.9)84 244 (2.7)450 (1.9)Aboriginal
58 305 (3)440 (3.8)81 852 (2.7)819 (3.5)Receiving social assistance
249 150 (12.8)1788 (15.4)389 597 (12.8)3357 (14.3)Rural residence
Comorbidities:
0 (0–1)0 (0–1)0 (0–0)0 (0–1)Median (IQR) Charlson
score‡
394 661 (20.3)3573 (30.8)252 467 (8.2)3766 (15.9)Hypertension
11 216 (0.6)5796 (49.9)4150 (.1)4056 (17.1)Prior nephrolithiasis§
IQR=interquartile range. CKD chronic kidney disease
*Full set of 3 089 194 eligible patients without end stage renal disease at baseline.
†Subset of 1 954 836 patients with serum creatinine measurements available.
‡Charlson score includes AIDS/HIV, metastatic cancer, non-metastatic cancer, cerebral vascular disease, chronic obstructive pulmonary disease, dementia,
diabetes, heart failure, mild liver disease, moderate/severe liver disease, myocardial infarction, paraplegia, peptic ulcer, peripheral vascular disease, and
rheumatological disease.
§Nephrolithiasis occurring within 3 years or 8 years before follow-up period in the registry and laboratory dataset respectively.
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BMJ 2012;345:e5287 doi: 10.1136/bmj.e5287 (Published 30 August 2012) Page 5 of 8
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Page 5
Table 2| Presence of kidney stones* and risk of adverse renal outcomes (end stage renal disease, chronic kidney disease (stage 3b–5),
and doubling of serum creatinine concentration). Values are multivariable adjusted hazard ratios† (95% confidence intervals) unless stated
otherwise
Doubled serum creatinineChronic kidney diseaseEnd stage renal disease
6574/1 952 198 (0.3)68 453/1 952 198 (3.5)5306/3 068 816 (0.2)No of events/No of patients (%)
1.94 (1.56 to 2.43)1.74 (1.61 to 1.88)2.16 (1.79 to 2.62)First kidney stone episode during follow-up
(v no stone)
1.001.001.00No stones
1.84 (1.43 to 2.36)1.73 (1.58 to 1.88)2.11 (1.69 to 2.63)Single kidney stone episode during follow-up
(v no stone)
2.22 (1.49 to 3.33)1.63 (1.37 to 1.95)2.31 (1.66 to 3.21)≥2 kidney stone episodes during follow-up
(v no stone)
<0.001<0.001<0.001P value for trend (No of stone episodes)
*Kidney stones were treated as a time-varying exposure: all participants were classified as “unexposed” at the start of follow-up, but, once a kidney stone occurred,
participants were classified as “exposed” for the remainder of the study.
†Results were adjusted for age (18–49.9, 50–69.9, ≥70 years), sex, Aboriginal, receipt of social assistance, rural residence, comorbidities (Charlson score and
hypertension), and prior nephrolithiasis. New stage 3b–5 chronic kidney disease and doubling of serum creatinine were evaluated in a subset of 1 954 836 patients
and also adjusted for baseline estimated glomerular filtration rate. The referent group for all analyses was those who had no stone during follow-up.
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Table 3| Presence of kidney stones* and risk of adverse renal outcomes (end stage renal disease, chronic kidney disease (stage 3b–5),
and doubling of serum creatinine concentration) with one-way stratification on age and sex. Values are multivariable adjusted hazard
ratios† (95% confidence intervals) unless stated otherwise
Doubled serum creatinineChronic kidney diseaseEnd stage renal disease
Age
≥50 years:
5443/795 087 (0.7)64 471/794 709 (8.1)3554/722 035 (0.5)No of events/No of patients (%)
1.77 (1.38 to 2.25)1.63 (1.50 to 1.77)2.01 (1.61 to 2.49)First kidney stone episode during follow-up (v
no stone)
<50 years:
1131/1 169 121 (0.1)3982/1 169 088 (0.3)1762/2 370 325 (0.07)No of events/No of patients (%)
3.38 (2.14 to 5.34)3.65 (2.92 to 4.55)2.81 (1.96 to 4.03)First kidney stone episode during follow-up (v
no stone)
0.01<0.0010.11P value for interaction of age and kidney stones
Sex
Male:
3275/883 756 (0.4)29 325/883 472 (3.6)3270/1 558 442 (0.2)No of events/No of patients (%)
1.70 (1.30 to 2.21)1.67 (1.52 to 1.83)1.87 (1.49 to 2.34)First kidney stone episode during follow-up (v
no stone)
Female:
3299/1 080 452 (0.3)39 128/1 080 128 (3.6)2036/1 533 918 (0.1)No of events/No of patients (%)
2.65 (1.87 to 3.77)1.94 (1.69 to 2.24)3.36 (2.42 to 4.66)First kidney stone episode during follow-up (v
no stone)
0.030.060.003P value for interaction of sex and kidney stones
*Kidney stones were treated as a time-varying exposure: all participants were classified as “unexposed” at the start of follow-up, but, once a kidney stone occurred,
participants were classified as “exposed” for the remainder of the study.
†Results were adjusted for age (18–49.9, 50–69.9, ≥70 years), sex, Aboriginal, receipt of social assistance, rural residence, comorbidities (Charlson score and
hypertension), and prior nephrolithiasis. New stage 3b–5 chronic kidney disease and doubling of serum creatinine were evaluated in a subset of 1 954 836 patients
and also adjusted for baseline estimated glomerular filtration rate. The referent group for all analyses was those who had no stone during follow-up.
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Figures
Fig 1 Patient flow through study
Fig 2 Forest plot of multivariable adjusted hazard ratios for kidney stones and ESRD. Absolute rates are ESRD rates per
1 000 000 person days
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