Nephrol Dial Transplant (2006) 21: 2152–2158
doi:10.1093/ndt/gfl221
Advance Access publication 15 May 2006
Original Article
Are prediction equations for glomerular filtration rate useful for
the long-term monitoring of type 2 diabetic patients?
Néstor Fontseré1, Isabel Salinas2, Jordi Bonal1, Beatriz Bayés1, Joaquim Riba3, Ferran Torres4,
Jose Rios4, Ana Sanmartı́2 and Ramón Romero1
1
Department of Nephrology, 2Department of Endocrinology and 3Department of Nuclear Medicine,
University Hospital Germans Trias i Pujol, Badalona and 4Biostatistics and Epidemiology Laboratory,
Universidad Autónoma de Barcelona, Barcelona, Spain
Abstract
Background. The aim of this study was to compare the
accuracy of prediction equations [modification of diet
in renal disease (MDRD), simplified MDRD,
Cockcroft–Gault (CG), reciprocal of creatinine and
creatinine clearance] in a cohort of patients with type 2
diabetes.
Methods. A total of 525 glomerular filtration rates
(GFRs) using 125I-iothalamate were carried out over
10 years in 87 type 2 diabetic patients. Accuracy was
evaluated at three levels of renal function according
to the baseline values obtained with the isotopic
method: hyperfiltration (GFR: >140 ml/min/1.73 m2;
140 isotopic determinations in 27 patients), normal
renal function (GFR: 140–90 ml/min/1.73 m2; 294
isotopic determinations in 47 patients) and chronic
kidney disease (CKD) stages 2–3 (GFR: 30–89 ml/min/
1.73 m2; 87 isotopic determinations in 13 patients). The
annual slope for GFR (change in GFR expressed as
ml/min/year) was considered to ascertain the variability in the equations compared with the isotopic
method during follow-up. Student’s t-test was used
to determine the existence of significant differences
between prediction equations and the isotopic method
(P < 0.05 with Bonferroni adjusted for five contrast
tests).
Results. In the subgroup of patients with hyperfiltration, a GFR slope calculated with 125I-iothalamate
4.8 4.7 ml/min/year was obtained. GFR slope in
patients with normal renal function was 3.0 2.3 ml/
min/year. In both situations, all equations presented a
significant underestimation compared with the isotopic
GFR (P < 0.01; P < 0.05). In the subgroup of CKD
stages 2–3, the slope for GFR with 125I-iothalamate
was 1.4 1.8 ml/min/year. The best prediction
Correspondence and offprint requests to: Néstor Fontseré Baldellou,
Department of Nephrology, Hospital de Terrassa, Ctra
Torrebonica s/n, 08227, Terrassa, Barcelona, Spain.
Email: [email protected]
equation compared with the isotopic method proved
to be MDRD with a slope for GFR of 1.4 1.3 ml/
min/year (P: NS) compared with the CG formula
1.0 0.9 ml/min/year (P: NS). Creatinine clearance
presented the greatest variability in estimation
(P < 0.001).
Conclusions. In the normal renal function and hyperfiltration groups, none of the prediction equations
demonstrated acceptable accuracy owing to excessive
underestimation of renal function. In CKD stages 2–3,
with mean serum creatinine 133 mmol/l (1.5 mg/dl),
the MDRD equation can be used to estimate GFR
during the monitoring and follow-up of patients with
type 2 diabetes receiving insulin, anti-diabetic drugs
or both.
Keywords: CKD stages 2–3; glomerular filtration rate;
hyperfiltration; normal renal function; prediction
equations; type 2 diabetic patients
Introduction
Data from the US Renal Data System predict that
the number of patients registered with end-stage renal
disease (ESRD) in 1997 will have doubled by 2010,
leading to approximately 700 000 patients with ESRD
and 2.2 million patients in 2030 [1]. According to
the current epidemiological data, type 2 diabetes is
considered to be one of the most frequent causes of
terminal chronic renal insufficiency and inclusion
in renal substitution programmes. Simple, purified
monitoring of renal function is of vital importance in
this subgroup of patients for therapeutic measures
aimed at reducing associated comorbidity factors to
be applied early.
Isotopic determination of the glomerular filtration
rate (GFR) would be the gold standard method for
determining renal function; however, it is an expensive
option and not often used in clinical practice.
ß The Author [2006]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved.
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Accuracy of prediction equations in patients with diabetes
The Cockcroft–Gault formula (CG) is probably one
of the most widely used prediction equations for the
follow-up of renal function and for the dose adjustment of potentially nephrotoxic drugs [2]. The CG
formula is an estimate of creatinine clearance originally
developed in a population of 236 Canadian patients
(209 males) with normal renal function and chronic
kidney disease (CKD) stages 2–3 (creatinine clearance:
114.9–37.4 ml/min). The modification of diet in renal
disease (MDRD) equation is the newest equation,
used in demographic, biochemical and nutritional
studies [3]. The MDRD formula was developed as an
estimation of 125I-iothalamate renal clearance-based
GFR measurement in a population of 1628 patients,
with CKD stages 3–4 (mean GFR: 39.8 21.2 ml/min/
1.73 m2). Both equations have been validated and
analysed in large patient populations with chronic
renal insufficiency, although their predictive capacity
has been analysed little in other levels of renal function
during the long-term follow-up of type 2 diabetes
mellitus (DM) patients [3].
The aim of our study was to compare renal function
and annual slope for GFR determined with the
isotopic method and the different prediction equations
[MDRD, simplified MDRD (sMDRD), CG and
reciprocal of creatinine] and with the measurement of
creatinine clearance using 24 h urine collection during
the follow-up in a cohort of patients with type 2
diabetes.
Subjects and methods
Study population
A total of 525 isotopic determinations of GFR were carried
out between October 1989 and November 2003 in 87 patients
with type 2 DM (53 women/34 men). All patients included
in the study fulfilled the American Diabetes Association
diagnostic criteria for type 2 DM, and were followed at the
out-patient clinic of a third-level hospital. Mean initial age of
the study group was 54 8.5 years (range: 31–69) and mean
known years of type 2 DM evolution 10.7 7.2 years (range:
1–31). Initially, 40.7% were under insulin treatment and 60%
in the final period. The control mean using the isotopic
technique was 10.2 2.2 years (range: 7–15). Renal function
was monitored in each patient using isotopic GFR
2153
125
I-iothalamate during the
determination calculated by
ambulatory follow-up period. Simultaneously with each
isotopic determination, demographic (age and sex), anthropometric (weight, height and body surface) and biochemical
(serum and urinary creatinine, urea nitrogen and albumin)
data were collected during the follow-up period with the
aim of establishing the estimation and calculation of renal
function using each of the prediction equations of different
levels. Data of all diabetic patients at baseline and the last
observation during the follow-up period are summarized
in Table 1.
According to the baseline values obtained with the isotopic
GFR, patients were divided into three study subgroups:
normal renal function [GFR between 140 and 90 ml/min/
1.73 m2 (294 isotopic determinations during the follow-up
period in 47 type 2 DM patients)]; hyperfiltration [GFR
>140 ml/min/1.73 m2 (144 isotopic determinations during
the follow-up period in 27 type 2 DM patients)] defined
according to the results obtained in our previous study [4]
and CKD stages 2–3 [GFR between 89 and 30 ml/min/
1.73 m2 (87 isotopic determinations during the follow-up
period in 13 type 2 DM patients)].
Study design and methods
Isotopic GFR was measured every 24 months (range: 12–36
months) by a single-shot clearance technique using an
intravenous injection of 30–50 mCi 125I-iothalamate [5];
blood was drawn at timed intervals and values were corrected
for body surface area of 1.73 m2. Preparation of the dose
administered to each patient was carried out using
an analytical balance and measurement of the tracer in
an activity meter. To obtain the standard samples of
125
I-iothalamate in each patient, the tracer was diluted in a
250 ml matrix, taking three 1 ml aliquots using a 1000 ml
micropipette. A 19 G peripheral catheter was inserted in each
patient for blood sample collection. Blood was extracted at
0, 5, 10, 15, 20, 25, 30, 40, 50, 60, 90, 120, 180 and 240 min.
In each study subgroup, the GFR value obtained with the
isotopic method was compared with the following prediction
equations:
(i) CG [2]
(a) Men: (140 age) weight (kg)/72 SCr.
(b) Women: [(140 age) weight (kg)/72 SCr] 0.85.
(ii) MDRD
[3]:
170 (SCr)0.999 (age)0.176 0.170
0.318
(Alb)
(0.762) female sex.
(BUN)
Table 1. Clinical and analytical data of 87 type 2 DM patients at baseline and the last observation during the follow-up period
Baseline
Body mass index (kg/m2)
Systolic pressure (mmHg)
Diastolic pressure (mmHg)
Hb A1c (%)
Albumin (g/dl)
Creatinine (mmol/l)
UAER (mg/24 h)
GFR (ml/min/1.73 m2)
28.9 5.5
142.6 25.7
77.5 11.9
7.3 1.9
4.4 0.5
85.7 26.5
259.0 603.2
118.9 36.9
Final
(17.3–42.0)
(90–210)
(60–110)
(5.5–13.6)
(3.3–5.1)
(55–198)
(2–3600)
(38.7–208.8)
UAER, urinary albumin excretion rate; GFR, glomerular filtration rate calculated with
All data are expressed as mean SD (minimum–maximum).
30.9 5.6
144.9 22.2
74.1 8.1
7.5 1.4
4.1 0.3
99.8 45
387.8 1131.3
91.5 35.1
125
I-iothalamate.
(21.1–46.4)
(100–198)
(58–100)
(5.6–12.5)
(2.7–4.7)
(59.2–396.9)
(2–3600)
(30–225)
2154
N. Fontseré et al.
1.154
0.203
(iii) sMDRD [6]: 186 (SCr)
(age)
(0.762)
female sex.
(iv) Reciprocal of creatinine: 100/SCr.
(v) Creatinine clearance: Ucr Vo/min (diuresis 24 h/
1440 min)/(SCr).
where SCr, serum creatinine (mg/dl): UCr, 24 h urinary
creatinine (mg/dl): Vo, urine volume: BUN, blood urea
nitrogen [urea (mg/dl)/2.14] and Alb, serum albumin (g/dl).
Blood samples were obtained simultaneously with
the GFR measurement. Biochemical parameters (glucose,
albumin, urea nitrogen concentration) were measured using
an autoanalyser (Technicon Autoanalyzer, Tarrytown,
New York, USA). Hb A1c was first measured by chromatography (Biosystem, Barcelona, Spain; normal range:
5.0–6.7%) and, since 1995, with a glycated haemoglobin
analyser using ion-exchange chromatography HPLC
(Hitachi L-9100; normal range: 3.3–5.0%). Urinary albumin
excretion rate (UAER) was measured by nephelometry
(CV: inter-assay 5%, intra-assay 3%, sensitivity 1.9 mg/l).
All serum and urinary creatinine measurements were
performed in the same laboratory and determined by
the Jaffé alkaline picrate method (normal range of SCr:
0.6–1.5 mg/dl), and calibrated using the SETpoint Calibrator
(Bayer CorporationÕ ).
All the patients included in the study provided written
informed consent and were informed of the form of
collection and conservation of the 24 h urine sample prior
to analytical processing at our centre. For routine analysis
and microscopic evaluation of the sample, the patient had to
void into a clean container. The specimen was conserved and
sent to our centre capped, labelled and refrigerated. Once in
our biochemistry laboratory, two-concentration level control
samples were used to guarantee reliability and validity of the
analytical results obtained.
Blood pressure was measured in the right arm with the
patient in a supine position, using a standard mercury
sphygmomanometer. Subjects rested for 15 min prior to the
blood pressure recording, which was taken twice (mean
recorded).
Statistical analysis
In each of the three study subgroups (normal renal function,
hyperfiltration and CKD stages 2–3), the annual slope for
GFR (change in GFR expressed as ml/min/year) was used to
assess the variability of the prediction equations compared
with the isotopic method during the follow-up period. This
parameter was determined in each isotopic GFR control for
each prediction equation, and compared with respect to its
basal values obtained at the start of follow-up. Student’s
t-test was used to determine the existence of significant
differences between prediction equations and the isotopic
method (P < 0.05 with Bonferroni adjusted for five contrast
tests). Pairwise comparisons between the estimation of
predictive equations and the isotopic method were made by
the method of Bland and Altman [7]. The SAS v 8.2 software
(Ref. SAS v 8.2, SAS Institute Inc.; Cary, NC, USA) was
used for the statistical analysis.
Results
The cohort of patients with type 2 diabetes was
followed using isotopic determination of GFR for
a mean of 10.2 2.2 years (range: 7–15). A mean of
six isotopic GFR (range: 4–8) was determined during
the follow-up period in all patients. The mean value
of GFR with 125I-iothalamate during the follow-up
period was 101.8 35.6 ml/min/1.73 m2 (range:
30–225). The accuracy of the prediction equations
expressed as the slope for GFR (ml/min/year) in
each of the three groups (normal renal function, hyperfiltration and CKD stages 2–3) is summarized in
Tables 2 and 3.
Table 2. Comparison of prediction equations in normal renal function and hyperfiltration groups of type 2 DM patients during the follow-up
period
Method of GFR estimation
*Normal renal function
125
I-iothalamatea
MDRD
sMDRD
CG
100/SCr
Creatinine clearance
**Hyperfiltration
125
I-iothalamatea
MDRD
sMDRD
CG
100/SCr
Creatinine clearance
a
Mean baseline value
Slope for GFRb (ml/min/year)
P-valuec
115.3 14.0
67.7 15.0
69.1 15.0
74.1 14.0
102.2 17.2
78.1 40.1
3.0 2.3
1.0 1.9
0.7 1.5
0.9 1.4
0.3 1.9
þ0.1 4.9
–
0.0005
0.0005
0.0005
0.0005
0.0005
159.0 18.6
78.2 16.8
88.5 31.9
98.0 25.3
122.5 37.9
77.3 31.4
4.8 4.7
0.8 2.3
1.0 2.5
1.2 2.5
0.9 3.1
þ1.8 9.2
–
0.0010
0.0010
0.0015
0.0005
0.0345
GFR by 125I-iothalamate clearance (ml/min/1.73 m2).
Slope for GFR (change/year) calculated as ml/min/1.73 m2/year.
c
Student’s t-test: GFR slopes obtained with different methods compared with 125I-iothalamate [the reference method (Bonferroni adjusted)].
MDRD, MDRD equation (ml/min/1.73 m2); sMDRD, simplified MDRD equation (ml/min/1.73 m2); CG, Cockcroft–Gault formula
(ml/min/1.73 m2); 100/SCr, reciprocal of creatinine [100/SCr (mg/dl)] and creatinine clearance (ml/min/1.73 m2).
*Normal renal function: 294 125I-iothalamate determinations during the follow-up period in 47 type 2 DM patients. **Hyperfiltration: 144
125
I-iothalamate determinations during the follow-up period in 27 type 2 DM patients. All data are expressed as mean SD.
b
Accuracy of prediction equations in patients with diabetes
2155
Table 3. Comparison of prediction equations in CKD stages 2–3 of type 2 DM patients during the follow-up period
Method of GFR estimation
Mean baseline value
Slope for GFRb (ml/min/year)
P-valuec
*CKD stages 2–3
125
I-iothalamatea
MDRD
sMDRD
CG
100/SCr
Creatinine clearance
71.2 13.9
52.6 23.8
53.7 22.6
57.6 20.4
79.8 33.9
68.3 46.2
1.4 1.8
1.4 1.3
1.3 1.4
1.0 0.9
1.0 1.4
+2.3 8.1
–
1.000
1.000
1.000
1.000
0.0005
a
GFR by 125I-iothalamate clearance (ml/min/1.73 m2).
Slope for GFR (change/year) calculated as ml/min/1.73 m2/year.
c
Student’s t-test: GFR slopes obtained with different methods compared with 125I-iothalamate [the reference method (Bonferroni adjusted)].
MDRD, MDRD equation (ml/min/1.73 m2); sMDRD, simplified MDRD equation (ml/min/1.73 m2); CG, Cockcroft–Gault formula
(ml/min/1.73 m2); 100/SCr, reciprocal of creatinine [100/SCr (mg/dl)] and creatinine clearance (ml/min/1.73 m2).
*CKD stages 2–3: 87 125I-iothalamate determinations during the follow-up period in 13 type 2 DM patients.
All data are expressed as mean SD.
b
In the normal renal function group [GFR: 140–90 ml/
min/1.73 m2 (294 125I-iothalamate determinations
during the follow-up period in 47 type 2 DM patients)],
the mean baseline value of isotopic GFR was
115.3 14 ml/min/1.73m2 (range: 90–140), with a
mean age of 58 8.5 years (31–77 years; 33 women/
14 men) and a mean SCr value during the follow-up
period of 90.1 19.4 mmol/l (range: 53.4–191.8). In this
group, the slope for GFR was 3.0 2.3 ml/min/year.
As shown in Table 2, all the prediction equations were
inaccurate compared with the isotopic GFR and
differed statistically and significantly (P < 0.01).
In the hyperfiltration group [GFR >140 ml/min/
1.73 m2 (144 125I-iothalamate determinations during
the follow-up period in 27 type 2 DM patients)],
the mean baseline value of isotopic GFR was
159 18.6 ml/min/1.73 m2 (range: 140–208.8), with a
mean age of 52 9.2 years (31–71 years; 14 women/
13 men) and a mean SCr value during the follow-up
period of 81.3 17.6 mmol/l (range: 35.3–142.3). In this
group, the slope for GFR during the follow-up period
was 4.8 4.7 ml/min/year. As shown in Table 2, all
the prediction equations were inaccurate compared
with the isotopic GFR and differed statistically and
significantly (P < 0.01; P < 0.05).
Finally, in CKD stages 2–3 group [GFR: 89–30 ml/
min/1.73 m2 (87 125I-iothalamate determinations
during the follow-up period in 13 type 2 DM patients)],
the isotopic GFR value obtained was 71.2 13.9 ml/
min/1.73 m2 (range: 30–87), with a mean age of
63 7.9 years (44–79 years; 6 women/7 men) and a
mean SCr value during the follow-up period of
133.4 50.3 mmol/l (range: 51.2–302.3). In this group,
the slope for GFR during the follow-up period was
1.4 1.8 ml/min/year. As shown in Table 3, none of
the prediction equations, except creatinine clearance,
presented statistically significant differences compared
with the isotopic technique (P > 0.05). In this situation,
the best result during the follow-up period was
obtained with the MDRD equation, which presented
a slope for GFR of 1.4 1.3 ml/min/year (P: NS)
compared with the CG formula 1.0 0.9 ml/min/year
(P: NS).
Discussion
The main aim of this study was to evaluate the accuracy of different prediction equations for the ambulatory follow-up of a cohort of patients with type 2 DM.
From the results obtained, it can be concluded that
the application of these equations is inadequate in
situations of normal renal function and hyperfiltration.
Only in CKD stage 2 levels (GFR <90ml/min/1.73 m2)
can they be used (except creatinine clearance) in
the ambulatory accurate control of this group of
patients.
Isotopic GFR is considered to be the gold standard
for estimating renal function. At present, its determination using 125I-iothalamate is impossible since it is
not available on the market. However, it is not always
convenient to apply this method in clinical practice
owing to its high cost and lack of availability in
primary care centres. For this reason, several prediction equations have been developed for the estimation
of GFR from parameters easily measured in the clinic.
These equations have been applied in different patients
with diverse grades of renal function [8,9]. Very few
studies have evaluated the use of these equations in
patients with type 2 diabetes. In the study by Levey
et al. [3], in the validation of the MDRD equation
some of the 558 patients had chronic renal insufficiency caused by type 2 diabetes, although the exact
number is not specified. Furthermore, those authors
suggested the need to conduct studies aimed at
evaluating the application of that prediction equation
in type 2 diabetic patients. There are very few
published studies that analyse the monitoring of renal
function using the application of prediction equations.
One notable study was that conducted in 30 Pima
Indians with type 2 diabetes during a 4 year follow-up
at
baseline
and
GFR
>120 ml/min/1.73 m2
N. Fontseré et al.
400
400
350
GFR estimated by the simplified
MDRD formula
GFR estimated by the MDRD formula
2156
300
250
200
150
100
50
350
300
250
200
150
100
50
0
0
50
100
150
200
250
300
350
400
0
GFR (ml/min/1.73m2)
0
50
200
250
300
350
400
300
350
400
400
350
300
250
200
150
100
50
0
0
50
100
150
200
250
300
350
400
GFR estimated by the reciprocal of
creatinine formula
GFR estimated by the CG formula
150
GFR (ml/min/1.73m2)
400
350
300
250
200
150
100
50
0
GFR (ml/min/1.73m2)
0
50
100
150
200
250
GFR (ml/min/1.73m2)
400
GFR estimated by the creatinine
clearance formula
100
350
300
250
200
150
100
50
0
0
50
100
150
GFR
200
250
300
350
400
(ml/min/1.73m2)
Fig. 1. Cross-sectional comparison of standardized iothalamate clearance with five indirect methods of measuring renal function in 87 type 2
diabetic patients. Shaded regions represent error margins of 30% for agreement between each of the five methods and the 125I-iothalamate
method. The 95% distribution of differences between the methods of estimation and the reference method, expressed as percentages by the
method of Bland and Altman [7], were MDRD 68.4 to 4.1%, sMDRD 69.1 to 0.4%, CG formula 63 to 3.5%, reciprocal of
creatinine 53.8 to 50.1% and creatinine clearance 94.5 to 56.6%.
examination [10]. Among the conclusions, the authors
suggested the use of measurements of serum cystatin C
(100/cystatin C) during the follow-up of type 2 diabetic
patients with normal or elevated GFR, since it is the
best method for detecting early function decline. In
contrast, some studies have shown that cystatin C may
have significant limitations as a marker of kidney
function in certain diseases [11]. Unfortunately, at the
start of the study, cystatin C was not available at our
centre for us to be able to estimate GFR during the
follow-up of our cohort of type 2 DM patients. Recent
studies [12], conducted in hypertensive patients,
Accuracy of prediction equations in patients with diabetes
conclude that the mean renal extraction of cystatin C
was equal to the mean renal extraction of
125
I-iothalamate. However, the authors discuss the
application and use of cystatin C as a GFR marker,
owing to a lower glomerular sieving coefficient and
possible modifications subject to the action of some
antihypertensive agents (such as angiotensin converting enzyme inhibitors or angiotensin II antagonist)
also widely used in patients with diabetic nephropathy.
The estimation of renal function from the SCr
concentration is associated with numerous errors, e.g.
it is dependent on production proportional to muscle
mass, is influenced by age and sex and by variable
tubular secretion and reabsorption, is not very sensitive
to the initial reductions in glomerular filtration and is
subject to a minimal extrarenal elimination (intestinal).
The interference of chromogens [13] in the determination of SCr deserves special mention. Substances such
as glucose and ketone bodies can cause false elevation
in plasma concentrations up to 20%, resulting in
underestimation of creatinine clearance.
For all these reasons, we believe it is of interest to
study the behaviour of these equations in patients with
type 2 diabetes. From our work, which concurs with
those of the other authors [14], we believe creatinine
clearance to be the equation with less accuracy and
greater variability in the estimation of GFR during the
follow-up period [Figure 1], including the CKD stages
2–3 group (Table 3). This variability in estimation may
be attributed to problems in the collection of samples
and inter-hospital differences in calibration methods,
which result in over- and underestimation of renal
function [15].
As in previous studies [16], we showed the hyperfiltration situation, with a greater slope for GFR
compared with normal filters, to be a marker of poor
evolution and worse renal function deterioration in
type 2 diabetic patients. As in the abstract published
by Rossing et al. [17] and according to our results
(Table 2 and Figure 1), we believe these prediction
equations in hyperfiltration and normal renal function
to be inaccurate in normal clinical practice, since they
significantly underestimated the isotopic method
during the follow-up period (P < 0.05).
In accordance with the study by Viktorsdottir et al.
[18] conducted in non-diabetic patients, we believe
the predictive capacity of those equations to be limited
when kidney failure is absent. For this reason, their
application in the design of epidemiological studies
aimed at establishing the stratification of the different
CKD stages (published in the K/DOQI guidelines)
[19], and their correlation with different cardiovascular
risk factors, could lead to significant methodological
errors being made.
Our results coincide with those of Poggio et al. [20]
who proposed using the MDRD equation to monitor
diabetic patients with moderate-to-advanced kidney
disease. This premise is based on the cross-sectional
analysis made in the subgroup of 249 diabetic patients
with a GFR calculated with 125I-iothalamate of
24 21 ml/min/1.73 m2 (thus nearly classifiable as
2157
CKD stage 4). In view of our results, we consider the
MDRD equation to be the best prediction equation for
the ambulatory monitoring of type 2 diabetic patients.
Furthermore, we consider it necessary to conduct
European multicentre studies with this kidney function
range.
As shown in Table 3, it is from CKD stage 2 (GFR:
<90 ml/min/1.73 m2) that, with the exception of
creatinine clearance, the prediction equations can be
started to be used for the ambulatory monitoring of
this group of patients. During the follow-up period,
no statistically significant differences (P > 0.05) were
observed regarding the slope for GFR (change/year)
obtained using 125I-iothalamate. Figure 1 graphically
demonstrates how creatinine clearance proves to be
the equation with greater variability and inaccuracy,
even in situations of CKD stages 2–3. With respect
to reciprocal of creatinine, we believe it excessively
overestimates the GFR and, in more advanced stages
of chronic renal insufficiency, could lead to severe
errors being made in the application of therapeutic
measures aimed at programming substitution renal
treatment.
In conclusion, based on our results, the use of the
prediction equations during the follow-up period of
type 2 diabetic patients proved inaccurate in cases of
hyperfiltration and normal renal function. It is in
situations of CKD stages 2–3 (GFR: 89–30 ml/min/
1.73 m2), with mean SCr levels 133 mmol/l (1.5 mg/dl),
that the MDRD equation can be started to be used for
GFR estimation during the monitoring and follow-up
of patients with type 2 diabetes receiving insulin and/or
oral anti-diabetic drugs.
Acknowledgements. The authors wish to thank Ms. Christine
O’Hara for help with the English version of the manuscript.
Conflict of interest statement. None declared.
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Received for publication: 24.11.05
Accepted in revised form: 29.3.06