original article
The
new engl a nd jour nal
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n engl j med 369;10 nejm.org september 5, 2013
932
Cystatin C versus Creatinine in Determining
Risk Based on Kidney Function
Michael G. Shlipak, M.D., M.P.H., Kunihiro Matsushita, M.D., Ph.D.,
Johan Ärnlöv, M.D., Ph.D., Lesley A. Inker, M.D., Ronit Katz, D.Phil.,
Kevan R. Polkinghorne, F.R.A.C.P., M.Clin.Epi., Ph.D.,
Dietrich Rothenbacher, M.D., M.P.H., Mark J. Sarnak, M.D.,
Brad C. Astor, Ph.D., M.P.H., Josef Coresh, M.D., Ph.D., Andrew S. Levey, M.D.,
and Ron T. Gansevoort, M.D., Ph.D., for the CKD Prognosis Consortium*
The authors’ affiliations are listed in the
Appendix. Address reprint requests to
Dr. Coresh at the Chronic Kidney Disease
Prognosis Consortium Data Coordinat-
ing Center, 615 N. Wolfe St., Baltimore,
MD 21205, or at ckdpc@jhmi.edu.
* A complete list of members of the
Chronic Kidney Disease (CKD) Prognosis
Consortium is provided in the Supple-
mentary Appendix, available at NEJM.org.
N Engl J Med 2013;369:932-43.
DOI: 10.1056/NEJMoa1214234
Copyright © 2013 Massachusetts Medical Society.
Abstr act
Background
Adding the measurement of cystatin C to that of serum creatinine to determine the
estimated glomerular filtration rate (eGFR) improves accuracy, but the effect on
detection, staging, and risk classification of chronic kidney disease across diverse
populations has not been determined.
Methods
We performed a meta-analysis of 11 general-population studies (with 90,750 par-
ticipants) and 5 studies of cohorts with chronic kidney disease (2960 participants)
for whom standardized measurements of serum creatinine and cystatin C were
available. We compared the association of the eGFR, as calculated by the measure-
ment of creatinine or cystatin C alone or in combination with creatinine, with the
rates of death (13,202 deaths in 15 cohorts), death from cardiovascular causes
(3471 in 12 cohorts), and end-stage renal disease (1654 cases in 7 cohorts) and as-
sessed improvement in reclassification with the use of cystatin C.
Results
In the general-population cohorts, the prevalence of an eGFR of less than 60 ml per
minute per 1.73 m
2
of body-surface area was higher with the cystatin C–based
eGFR than with the creatinine-based eGFR (13.7% vs. 9.7%). Across all eGFR cate-
gories, the reclassification of the eGFR to a higher value with the measurement of
cystatin C, as compared with creatinine, was associated with a reduced risk of all
three study outcomes, and reclassification to a lower eGFR was associated with an
increased risk. The net reclassification improvement with the measurement of cys-
tatin C, as compared with creatinine, was 0.23 (95% confidence interval [CI], 0.18
to 0.28) for death and 0.10 (95% CI, 0.00 to 0.21) for end-stage renal disease. Re-
sults were generally similar for the five cohorts with chronic kidney disease and
when both creatinine and cystatin C were used to calculate the eGFR.
Conclusions
The use of cystatin C alone or in combination with creatinine strengthens the as-
sociation between the eGFR and the risks of death and end-stage renal disease
across diverse populations. (Funded by the National Kidney Foundation and others.)
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Cystatin C vs. Creatinine to Determine Kidney Risk
n engl j med 369;10 nejm.org september 5, 2013
933
T
he estimated glomerular filtra-
tion rate (eGFR) is the clinical standard
for the assessment of kidney function.
1-3
The eGFR thresholds for the definition and stag-
ing of chronic kidney disease are based on risk,
3
but measurement of creatinine to determine the
eGFR has limitations in risk prediction, particu-
larly in patients with reduced muscle mass.
4
Cys-
tatin C has received much attention as an alter-
native filtration marker with stronger and more
linear risk relationships than creatinine.
5-7
Several
studies have suggested that the addition of cys-
tatin C measurements to creatinine measurements
in calculating the eGFR significantly improves
the risk classification for death, cardiovascular
disease, and end-stage renal disease.
8-10
However, existing evidence has been limited
by the lack of a reference standard for cystatin C
to calibrate the measures across studies and by
the absence of cystatin C–based equations that
are derived from a broad population with a wide
range of kidney function. The development of an
international reference standard for cystatin C
and the publication of improved GFR-estimating
equations by the Chronic Kidney Disease Epide-
miology Collaboration
11
prompted the current
meta-analysis of 16 studies across a diverse
population of participants. The objectives of this
study, which was conducted by the Chronic Kid-
ney Disease Prognosis Consortium (CKD-PC),
were to determine whether the addition of an
eGFR that was calculated with the use of the
recently developed cystatin C equations would
strengthen the relationships between various
eGFR categories and adjusted risks of death from
any cause, death from cardiovascular causes, and
end-stage renal disease, as compared with the
use of creatinine-based eGFR.
Methods
Study Design and Participants
Detailed descriptions of the CKD-PC have been
reported previously.
12-15
To be eligible for inclu-
sion in the meta-analysis, studies had to include
at least 1000 participants (with the exception of
studies that enrolled only patients with chronic
kidney disease)
14
for whom data on baseline se-
rum creatinine and albuminuria were available.
In addition, studies had to include reports of at
least 50 events for any outcome of interest. This
meta-analysis included 11 general-population
studies (with 90,750 participants) and 5 studies of
patients with chronic kidney disease (with 2960
participants) for whom measurements of serum
cystatin C were available.
We calculated the eGFR using the latest equa-
tions from the Chronic Kidney Disease Epidemi-
ology Collaboration, with measurement of serum
creatinine, cystatin C, or both creatinine and
cystatin C (combination).
11,16-18
All three eGFR
equations incorporated kidney-filtration markers
(serum creatinine or cystatin C) as well as age,
sex, and race (black vs. nonblack), except for the
cystatin C–based eGFR, for which data on race
were not required.
For each study cohort, we attempted to cali-
brate cystatin C measurements to the reference
standard by evaluating the year and measure-
ment method used (Table S1 in the Supplemen-
tary Appendix, available with the full text of this
article at NEJM.org).
11,19
We first used the cys-
tatin C–based eGFR to reclassify participants who
were initially classified according to the creati-
nine-based eGFR. Comparing the cystatin C–based
eGFR with the creatinine-based eGFR had the
advantage of providing the clearest contrast,
since each equation includes only one filtration
marker. We then compared the creatinine equa-
tion with the combination equation.
Study Outcomes
The outcomes of interest were death from any
cause, death from cardiovascular causes, and end-
stage renal disease. Death from cardiovascular
causes was defined as death from myocardial in-
farction, heart failure, or stroke. End-stage renal
disease was defined by the need for renal-replace-
ment therapy or death from chronic kidney
disease.
We first performed analyses within each study
cohort and then performed meta-analyses across
all studies, using random-effects models. We re-
stricted our analysis to participants who were at
least 18 years of age. Primary analyses were con-
ducted in the general-population cohorts, since
participants were not selected on the basis of
serum creatinine levels. Secondary analyses were
performed in the cohorts with chronic kidney
disease.
Study Oversight
The study was designed by the CKD-PC steering
committee. Data were collected within each of
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n engl j med 369;10 nejm.org september 5, 2013
934
the 16 cohorts and analyzed centrally at the coor-
dinating center.
Statistical Analysis
We first evaluated the distributions for each
eGFR equation. Subsequently, we constructed
Cox proportional-hazards models fitted with
eGFR linear splines, with adjustment for age,
sex, race (black vs. nonblack), smoking status,
status with respect to a history of cardiovascular
disease, systolic blood pressure, presence or ab-
sence of diabetes, total cholesterol level, body-
mass index, and the level of albuminuria. From
these models, we computed and pooled hazard
ratios for each increment in the eGFR of 1 ml per
minute per 1.73 m
2
of body-surface area for
eGFR values from 15 to 120, with a reference
point at 95 ml per minute per 1.73 m
2
(50 ml per
minute per 1.73 m
2
for cohorts with chronic kid-
ney disease), as in previous CKD-PC meta-analy-
ses.
12-14,16,20,21
The reference point was moved to
65 ml per minute per 1.73 m
2
for the end point of
end-stage renal disease in the general-population
cohorts in order to ensure that there were suffi-
cient events at an eGFR value above the reference
point. Details about the statistical analysis are
Table 1. Baseline Characteristics of Participants in 11 General-Population Studies and 5 Studies of Chronic Kidney Disease.*
Study Country
No. of
Participants Mean Age
Female
Sex
Black
Race Estimated Glomerular Filtration Rate
Creatinine Cystatin C Combination
yr % of participants ml/min/1.73 m
2
General population
All studies 90,750 60 54 20 85 85 84
ARIC
28
United States 11,215 63±6 56 22 84±16 83±18 85±16
AusDiab
29
Australia 10,507 51±14 55 0 86±17 90±20 88±17
Beaver Dam CKD
30
United States 4,617 62±11 56 <1 80±18 79±21 79±19
CHS
31
United States 2,984 78±5 59 17 74±17 63±19 69±18
ESTHER
32
Germany 9,607 62±7 55 0 84±20 83±18 84±17
Framingham
33
United States 2,596 58±10 54 0 89±18 83±19 86±17
MESA
34
United States 6,693 62±10 53 28 82±16 89±20 86±18
NHANES III
35
United States 6,748 56±20 52 25 90±25 84±28 87±26
PREVEND
36
Netherlands 7,982 49±13 50 1 89±16 103±21 97±19
REGARDS
37
United States 26,698 64±10 54 43 87±21 84±21 84±21
ULSAM
38
Sweden 1,103 71±1 0 0 76±11 59±14 67±12
Chronic kidney disease
All studies 2,960 55 37 37 38 39 38
AASK
39
United States 949 55±11 39 100 46±15 45±18 44±15
CRIB
40
United Kingdom 292 62±14 34 6 22±11 22±12 21±11
MASTERPLAN
41
‡ Netherlands 473 59±13 31 3 36±14 46±21 40±17
MDRD
42
United States 1,044 52±13 39 10 35±15 32±14 32±14
MMKD
43
Austria 202 47±12 34 0 47±30 50±33 48±32
* Plus–minus values are means ±SD. AASK denotes African American Study of Kidney Disease and Hypertension, ARIC Atherosclerosis Risk
in Communities, AusDiab Australian Diabetes, Obesity, and Lifestyle, Beaver Dam CKD
Beaver Dam Chronic Kidney Disease Study, CHS
Cardiovascular Health Study, CRIB Chronic Renal Impairment in Birmingham, CVD cardiovascular disease, ESTHER
Epidemiologische Studie zu
Chancen der Verhütung, Früherkennung und optimierten Therapie chronischer
E
rkrankungen in der älteren Bevölkerung, Framingham Fram-
ingham Heart Study, MASTERPLAN
Multifactorial Approach and Superior Treatment Efficacy in Renal Patients with the Aid of a Nurse Prac-
titioner, MDRD
Modification of Diet in Renal Disease, MESA
Multi-Ethnic Study of Atherosclerosis, MMKD
Mild to Moderate Kidney Disease,
NA
not available, NHANES III Third U.S.
National Health and Nutrition Examination Survey, PREVEND Prevention of Renal and Vascular End-
Stage Disease, REGARDS Reasons for Geographic and Racial Differences in Stroke, and ULSAM
Uppsala Longitudinal Study of Adult Men.
† Listed are the proportions of participants with an albumin:creatinine ratio of 30 or more (with albumin measured in milligrams per deciliter
and creatinine in grams per deciliter), a protein:creatinine ratio of 50 or more (with protein measured in milligrams per deciliter and creati-
nine in grams per deciliter), or a dipstick protein value of 1+ or higher.
‡ Five participants were excluded from the analysis of incident end-stage renal disease.
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Cystatin C vs. Creatinine to Determine Kidney Risk
n engl j med 369;10 nejm.org september 5, 2013
935
provided in Appendix 1 in the Supplementary Ap-
pendix.
We cross-tabulated the eGFR that was calculat-
ed by means of each equation, using clinical cate-
gories of volume per minute per 1.73 m
2
(<15 ml,
15 to 29 ml, 30 to 44 ml, 45 to 59 ml, 60 to 89 ml,
and ≥90 ml).
1,22
We then evaluated the propor-
tion of participants in each creatinine-calculated
eGFR category for whom the eGFR was reclassi-
fied on the basis of the cystatin C measurement
or the combined measurement.
1,16,22-25
For each
outcome, we used multivariable Cox proportional-
hazards models to assess risks of adverse out-
comes among participants for whom the eGFR
was reclassified to a higher value (i.e., to high-
er categories of cystatin C–calculated eGFR or
combination-calculated eGFR) or a lower eGFR
value (i.e., to lower categories of the two sets of
GFR estimates), as compared with participants
for whom the eGFR was not reclassified.
We assessed the overall improvement in reclas-
sification on the basis of clinical eGFR categories
by applying the net-reclassification-improvement
approach,
25,26
a method involving the use of pre-
defined risk categories to assess improved risk
prediction. To assess generalizability, we calcu-
lated the net reclassification improvement in
subgroups according to age (<65 vs. ≥65 years),
sex, race (black vs. nonblack), eGFR category, and
status with respect to diabetes, hypertension, and
albuminuria, with a correction for bias when
appropriate.
27
All analyses were conducted with
the use of Stata/MP software, version 11.2.
Results
Study Outcomes
The mean values for the eGFR as measured with
creatinine, cystatin C, and a combination of both
for volume per minute per 1.73 m
2
were 85 ml,
85 ml, and 84 ml, respectively, among the general-
population cohorts and 38 ml, 39 ml, and 38 ml,
respectively, among the cohorts with chronic kidney
disease (Table 1).
28-43
In the general-population
Albumin uria†
Smoking
(%)
History
of CVD
Hypercholes-
terolemia
Hyper-
tension Diabetes
Mean
Follow-up Death
End-Stage
Renal Disease
Any Cause CVD
% of participants
yr
no. of participants
12 18 15 32 50 16 7.7 12,351 3193 357
8 15 14 34 48 17 10.6 1,884 383 186
6 16 8 44 32 6 9.9 832 172 NA
4 20 15 54 50 10 11.5 1,462 647 NA
20 8 31 38 64 16 8.4 1,729 655 NA
12 16 17 46 60 19 5.0 487 159 NA
11 15 6 22 39 9 10.7 186 92 NA
10 13 0 28 45 12 6.2 322 70 NA
16 22 16 NA 42 16 8.0 1,438 635 NA
11 34 5 39 34 4 9.7 602 170 NA
16 16 22 16 60 23 5.0 2,947 NA 171
16 20 36 58 75 19 11.6 462 210 NA
78 19 30 52 97 9 9.3 851 278 1297
61 29 51 43 100 0 8.8 216 NA 273
86 14 44 57 95 18 6.1 110 55 138
86 23 25 72 95 32 4.1 52 NA 66
84 10 13 NA NA 6 14.0 473 223 749
95 21 12 39 89 0 4.0 NA NA 71
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n engl j med 369;10 nejm.org september 5, 2013
936
cohorts, the prevalence of an eGFR of less than
60 ml per minute per 1.73 m
2
was 9.7% with the
creatinine equation, 13.7% with the cystatin C
equation, and 10.0% with the combination (Fig.
1), values that were consistent across subgroups
(Fig. S1 in the Supplementary Appendix).
Death from Any Cause
In the 11 general-population cohorts, 12,351 of
90,750 participants (13.6%) died during a mean
follow-up of 7.7 years. With a cystatin C–based
eGFR, the risk of death from any cause was in-
creased at eGFR values that were below the ref-
erence point of 95 ml per minute per 1.73 m
2
, with
a threshold of 88 ml per minute per 1.73 m
2
(i.e.,
the point at which the risk was significantly higher
than the risk at the reference point) (Fig. 2A). The
corresponding thresholds were 59 ml and 83 ml
per minute per 1.73 m
2
for the creatinine-based
eGFR and the combination-based eGFR, respec-
tively.
.
There was a reverse J-shaped association
for the creatinine and combination measurements
of eGFR, with a significantly elevated risk of
death at higher eGFR values, as has been reported
previously.
6
Among the cohorts of patients with chronic
kidney disease, eGFR values based on cystatin C
and combination measurements also had more
linear associations with the risk of death than
did the values based on creatinine measurement,
although no reverse J-shaped association was
observed for the creatinine-based eGFR values
(Fig. S2A in the Supplementary Appendix).
In the general-population cohorts, across all
the creatinine-based eGFR categories, reclassifi-
cation to a lower eGFR was associated with a sig-
nificantly higher adjusted risk of death (
Table 2
).
For example, among participants with a creatinine-
based eGFR of 60 to 89 ml per minute per 1.73 m
2
(48% of participants overall), 14% were reclassi-
fied to a cystatin C–based eGFR of less than 60 ml
per minute per 1.73 m
2
and had a relative increase
of 57% in the adjusted risk of death during fol-
low-up. Within the smaller category of a creati-
nine-based eGFR of 60 to 74 ml per minute per
1.73 m
2
(18% of all participants), the 23% who
were reclassified to a cystatin C–based eGFR of
less than 60 ml per minute per 1.73 m
2
also had a
significantly higher adjusted risk of death (hazard
ratio, 1.54; 95% confidence interval [CI], 1.33 to
1.79) (Table S2 in the Supplementary Appendix).
Conversely, across all categories of creatinine-
based eGFR values, reclassification to a higher
eGFR with the measurement of cystatin C was
associated with a reduction in the adjusted risk
of death, as compared with the group with eGFR
values that were not reclassified, although the
findings were significant only for creatinine-
based eGFR categories of 30 to 44 ml and 45 to
59 ml per minute per 1.73 m
2
. In the latter cate-
gory, 42% of participants were reclassified to a
cystatin C–based eGFR of 60 ml per minute per
1.73 m
2
or more and had a relative reduction of
34% in the adjusted risk of death. Similar results
were observed when findings were unadjusted or
further adjusted for the creatinine-based eGFR
(Tables S3 and S4 in the Supplementary Appendix).
Across all categories of creatinine-based eGFR
values, the overall net reclassification improve-
ment for death from any cause was 0.21 (95% CI,
0.17 to 0.26; P<0.001) and was greater in the
general-population cohorts than in those with
chronic kidney disease (Fig. 3). Among the 15 co-
horts for which mortality data were available, all
had positive net reclassification improvements. The
bias-corrected estimates of net reclassification im-
provement were highest for the creatinine-based
eGFR categories of 45 to 59 ml per minute per
1.73 m
2
(0.28; 95% CI, 0.19 to 0.36), 30 to 44 ml
per minute per 1.73 m
2
(0.32; 95% CI, 0.25 to
0.39), and 15 to 29 ml per minute per 1.73 m
2
(0.27; 95% CI, 0.18 to 0.37) (Table S5 in the Sup-
Density (%)
3
1
2
0
0 30 60 90 120 150
180
eGFR (ml/min/1.73 m
2
)
Creatinine
Cystatin C
Combination
Figure 1. Distribution of the Estimated Glomerular Filtration Rate (eGFR)
as Calculated with the Measurement of Creatinine, Cystatin C, or Both
in 11 General-Population Cohort Studies.
A total of 90,750 participants were included in the meta-analysis of 11 stud-
ies, with a kernel-density estimate showing the smoothed frequency for each
1 ml of the eGFR value. The vertical lines indicate current clinical thresholds
for eGFR categories.
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