Open Journal of Nephrology, 2013, 3, 184-188
Published Online December 2013 (
Open Access OJNeph
Two-Hour Creatinine Clearance and Glomerular Filtration
Rate Estimated from Serum Cystatin C and Creatinine
in the Elderly to Preoperative Period
Leopoldo Muniz da Silva, Pedro Thadeu Galvão Vianna, Mariana Takaku,
Glênio Bittencourt Mizubuti, Yara Marcondes Machado Castiglia*
Department of Anaesthesiology, Botucatu School of Medicine,
São Paulo State University (UNESP), São Paulo, Brazil
Email: *
Received July 22, 2013; revised August 18, 2013; accepted September 15, 2013
Copyright © 2013 Leopoldo Muniz da Silva et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Introduction: The utility of estimates of glomerular filtration rate based on creatinine and cystatin C serum levels to
assess renal function in older surgical patients remains to be determined. Objective: To determine whether
2h-creatinine clearance (CrCl-2h) can be an adequate substitute for glomerular filtration rate estimates obtained by
measuring serum cystatin C and creatinine in the elderly at preoperation. Methods: A total of 102 consecutive elder
patients undergoing pre-anesthesia evaluation for routine surgeries were included. Study subjects were allocated into
three groups: Group 1 (G1)—hypertensive diabetic patients, Group 2 (G2)—hypertensive patients, and Group 3
(G3)—non-hypertensive and non-diabetic patients. Two-hour urine collection was performed and CrCl-2h adjusted for
ultrasonic residual bladder volume was estimated. GFR was estimated based on creatinine and cystatin C serum levels.
Bland-Altman analysis was used to compare methods. Results: The mean difference between the evaluated methods
and CrCl-2h was <15 mL·min1·1.73 m2 for Cys-GFR, and >20 mL·min1·1.73 m2 for Cr-GFR in all groups. CrCl-2h
adjusted for ultrasonic residual bladder volume did not differ from non-adjusted CrCl-2h in none of the groups. Con-
clusion: Two-hour creatinine clearance was not an adequate substitute for GFR estimates based on creatinine and cys-
tatin C serum levels in older patients at preoperation. The ultrasonic assessment of residual bladder volume had no sig-
nificant influence on the calculation of two-hour creatinine clearance.
Keywords: Renal Function; Creatinine Clearance; Cystatin C; Elderly
1. Introduction
Subclinical renal disease, frequently seen in the diabetic
and long-term hypertensive elderly, increases the risk
associated with anesthesia and surgery, and enhances the
susceptibility of these individuals to intraoperative renal
failure, leading to high postoperative mortality rates
The collection of urine output over 24 hours is one of
the methods that have been used to assess renal function
as it eliminates the potential error due to the existence of
residual bladder volume, particularly in older people.
However, a 24-h urine collection may not be feasible
during preoperative evaluation delaying the availability
of information for clinical evaluation [4].
In 1988, Cardenas et al. [5] described a small portable
ultrasound device, specifically designed to determine
bladder volumes that can be operated with minimal train-
ing. According to these authors, volumes estimated using
this noninvasive method correlate with those obtained by
urethral catheterization. Thus, the assessment of renal
function at 2-h intervals using ultrasound bladder scan to
eliminate the bias associated with postmicturition resid-
ual volume would be useful for the preoperative evalua-
tion of elderly patients. Among intensive care patients,
2-h creatinine clearance has been demonstrated to be an
adequate substitute for 24-h clearance, even in unstable
patients [6].
Whether estimates of glomerular filtration rate based
on creatinine and cystatin C serum levels are compared
with 2-h creatinine clearance to assess renal function in
older patients remains to be determined. Despite being an
earlier marker of renal failure, cystatin C has not shown
*Corresponding author.
advantages over creatinine in the elderly [7]. Therefore,
the purpose of this study was to assess whether creatinine
clearance determined by a 2-hour urine collection ad-
justed for residual bladder volume is an adequate substi-
tute for glomerular filtration rate estimates obtained by
measuring serum cystatin C and creatinine in older pa-
tients before surgery.
2. Methods
This study was approved by the Committee of Research
Ethics of Botucatu Medical School, and written informed
consent was obtained from all subjects.
The study population consisted of 102 consecutive el-
derly patients (65 years) who underwent pre-anesthe-
sia evaluation for routine orthopedic, gastrointestinal,
vascular, or gynecologic surgery in a tertiary university
Study subjects were allocated into three groups: Group
1 (G1)—hypertensive diabetic patients, Group 2 (G2)—
hypertensive patients, and Group 3 (G3)—non-hyperten-
sive and non-diabetic patients. Patients were considered
hypertensive and diabetic when diagnosis and specific
treatment for these conditions had been established prior
to admission. Patients with heart failure, renal failure re-
quiring dialysis, anuria or kidney transplant were ex-
cluded. All patients had surgical diseases and were re-
ceiving preoperative in-patient care.
For renal function assessment, post-void residual urine
volume was checked using a BVI 5000 ultrasound scan-
ner (Diagnostic Ultrasound Corporation, USA). With the
patient lying supine, the scanhead was lubricated with
conductive gel (gel pad Sontac 50) and positioned ap-
proximately 5 cm above the symphysis pubis. Three
scans were performed on each subject and the mean vo-
lume from these scans was used as the mean urine vol-
ume. Time count was then started. Patients were asked to
complete urine collection in a special container for the
next two hours. After one hour, a blood sample (15 mL)
was obtained for the measurement of creatinine (mg/dL),
urea (mg/dL), cystatin C (mg/L), and glycated hemoglo-
bin (%). By the end of the two-hour interval, patients
were asked to void in a container. From the total urine
volume voided, a sample was collected for creatinine
assessment (mg/dL). Ultrasonic residual volume was
then measured again. Three readings were taken and the
mean volume from these readings was added to the
amount collected in the container. Adjusted urine volume
was estimated by subtracting the initial residual volume
from this sum. Urine output per minute (mL·min1) was
obtained by dividing the adjusted residual volume by the
time elapsed to obtain it. Two-hour creatinine clearance
(mL·min1), or two-hour glomerular filtration rate (GFR),
was estimated from the equation [urine creatinine (mg/dL)
× adjusted two-hour urine volume (mL/min1)/blood
creatinine (mg/dL)].
Serum cystatin C measurements were performed by
latex enhanced reagent (N Latex Cystatin C, Dade Behr-
ing, Deerfield, IL, USA) using a Behring BN ProSpec
analyser (Dade Behring) and Dade Behring calibrators.
The test was performed according to the in- structions of
the manufacturer. Serum creatinine was measured by a
dry chemistry technique at the Chemistry Laboratory of
the hospital.
Creatinine-estimated GFR was calculated by the
Cockcroft & Gault formula [8] where (GFRCG) = [140
age (years) × weight (kg) / 72 × blood creatinine (mg/dL)
× 0.85 (if female). GFR from cystatin C was calculated
by the Larsson et al. formula [9] where (GFRLarsson) =
[77.24 × cystatin C1.2623 (mg/L)]. GFR and two-hour
creatinine clearance were expressed per 1.73 m2 of body
surface area by multiplying measured values by 1.73 of
body surface area. Anthropometric data, such as age
(years), gender, weight (kg), height (m2) and body mass
index (kg/m2) were collected during preoperative clinical
Statistical Analysis
Sample size (n = 102) was calculated to detect a differ-
ence of at least 15% between GFR by serum creatinine
and two-hour creatinine clearance. Assuming a probabil-
ity of 5% for a type I error and 20% for a type II error, 34
patients in each group would allow two-tailed compari-
sons. Median and 25% - 75% percentiles were used as a
measure of central tendency and variability due to
non-normal distribution of the study data. Categorical
variables were reported as absolute values and percent-
ages. Comparisons were performed with the non-para-
metric Kruskal Wallis test for continuous variables, fol-
lowed by the a posteriori Dunn test for multiple com-
parisons if P > 0.05. Significance was set at P < 0.05.
CrCl-2h adjusted for ultrasonic residual bladder volume
and not adjusted CrCl-2h was compared by Mann-Whit-
ney test.
Because analysis with correlation and least squares li-
near regression is fundamentally misleading, Bland and
Altman analysis [10] was used to compare the differ-
ences between the methods for glomerular filtration rate
measurement (Y axis) plotted against their mean (X axis).
Bias was defined as the mean value of the differences
between methods. If the 95% limits of agreement (mean
± 2SD) between methods were not clinically important,
methods were considered interchangeable. The confi-
dence intervals for the 95% limits of agreement were
calculated by mean difference ±1.96 standard deviation
of the differences. Bland and Altman analysis [10] of the
GFR estimates was performed with Medcalc (Medical
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Cr-GFR - CrCl-2h were showed in Table 1.
Software, Mariakerke, Belgium).
CrCl-2h adjusted for ultrasonic residual bladder vol-
ume did not differ from non-adjusted CrCl-2h in all pa-
tients (Figure 2).
3. Results
Patient median age was 71 years (65 - 88 years). Males
accounted for 66.34% of the study population. In diabetic
patients, median glycated hemoglobin was 7.2%. 4. Discussion
The assessment of renal function using creatinine con-
centration as a marker has several limitations in the eld-
erly. Two hour-creatinine clearance would then be an im-
portant alternative for assessing renal function serially
and at short intervals.
Study groups were homogeneous according to age,
gender and body mass index (kg·m2). There was no sta-
tistically significant difference in adjusted urine volume,
two-hour creatinine clearance (CrCl-2h), creatinine-esti-
mated glomerular filtration rate (Cr-GFR) and Cystatin-C
estimated GFR (Cys-GFR). In this study, CrCl-2h was compared with glomerular
filtration rate and estimates from creatinine and cystatin
C. Our data showed that CrCl-2h better agreed with cys-
tatin C-estimated GFR (Larsson equation) than with
creatinine-estimated GFR (Cockcroft & Gault equation)
in older patients. The mean difference between the evalu-
ated methods and CrCl-2h was < 15 mL·min1·1.73 m2
for Cys-GFR, and >20 mL·min1·1.73 m2 for Cr-GFR in
all groups. A mean difference between methods of 18 -
The mean differences between the evaluated methods
and CrCl-2h were 3.67 mL·min1·1.73 m2 for Cys-GFR,
and 27.44 mL·min1·1.73 m2 for Cr-GFR in G1; 2.29
mL·min1·1.73 m2 for Cys-GFR and 22.96
mL·min1·1.73 m2 for Cr-GFR in G2; 13.10
mL·min1·1.73 m2 for Cys-GFR and 40.40
mL·min 1·1.73 m2 for CR-GFR in G3 (Figure 1).
Limits of agreement between Cys-GFR - CrCl-2h and
Figure 1. Bland-Altman plot for differences between Cys-GFR, Cr-GFR and two-hour creatinine clearance (CrCl-2h) per
group (G1-G3) in the preoperative period. Horizontal lines indicate the mean reflecting the mean difference and the span
between +1.96 SD and 1.96 SD of the mean difference between CrCl-2h and the methods evaluated (Cys-GFR and Cr-GFR).
Table 1. Bland-Altman for differences between Cys-GFR, Cr-GFR and two-hour creatinine clearance (CrCl-2h) per group
(G1-G3) in the preoperative period. Limits of agreement - Upper limit (+1.96 SD) (CI 95%) and lower limit (1.96 SD) (CI
95%) (mL·min1·1.73 m2).
Limits of agreement Groups
Cystatin C-GFR* G1 G2 G3
Upper limit (CI 95%) 187.50 (131.02; 144.03) 149.58 (99.74; 190.26) 218.60 (155.46; 281.75)
Lower Limit (CI 95%) 180.26 (236.77; 126.76) 145.00 (194.55; 104.33) 192.40 (255.54; 129.26)
Upper limit (CI 95%) 220.73 (161.35; 280.14) 171.62 (125.96; 217.33) 250.51 (183.65; 315.89)
Lower Limit (CI 95%) 165.85 (225.25; 106.46) 125.80 (171.4; 80.03) 169.71 (239.70 ; 107.47)
*mL·min1·1.73 m2.
Figure 2. Comparison of CrCl-2h adjusted (B) and not ad-
justed (A) for ultrasonic residual bladder volume
(mL·min1·1.73 m2) in elder patients during the preopera-
tive period. Box plots - Bars represent median values, boxes
represent interquartile ranges, and whishers show 95%
confidence intervals. Mann-Whitney Test: A = B in G1, G3
and G3.
20 mL·min1·1.73 m2 [6] was considered acceptable.
However, although CrCl-2h values showed a better
agreement with Cys-GFR, the wide limits of agreement
between these methods, which reflect the great variation
of the results obtained, did not allow concluding that
these methods actually agree and can be used inter-
In intensive care patients, Gutierrez et al. [6] found a
close correlation between 24-h and 2-h creatinine clear-
ance that remained even with the use of diuretics or in
the presence of low or irregular diuresis, suggesting that
such methods are interchangeable. These authors further
report that 24-h creatinine clearance correlated poorly
with GFR estimated by the Cockcroft & Gault equation.
Diabetes and hypertension, which have the kidney as a
target organ, tend to worsen renal function in older pa-
tients. The diabetic and hypertensive elderly included in
this study was receiving preoperative care for routine
surgery, and was, therefore, well compensated. Moreover,
those who were diabetic had satisfactory previous gly-
cemia control as measured by glycated hemoglobin. This
fact may explain why no difference in preoperative renal
function was detected among groups.
Studies comparing cystatin C with creatinine meas-
urements have produced conflicting results. While some
have demonstrated that cystatin C is more sensitive than
creatinine in detecting renal failure [11-13], others have
reported no difference between these markers [7,14].
This disparity is likely to be due to differences in study
population. In patients with normal or slightly reduced
renal function, cystatin C seems to be superior to creati-
nine. In contrast, in patients with a marked decline in
renal function, differences between cystatin C and creati-
nine are smaller as frequently observed in older patients
Because the formula of Cockcroft & Gault may over-
estimate renal function when GFR >60 mL·min1·1.73
m2, cystatin C is clearly more useful in these cases. In
this study, in which individuals with markedly reduced
renal function were not included and most elderly pa-
tients showed GFR >60 mL·min1·1.73 m2, cystatin C
was a more adequate marker of renal function than
CrCl-2h [15]. The Cockcroft & Gault formula might
have overestimated GFR, and this would explain the in-
creased difference between mean CrCl-2h and mean
Cockcroft & Gault formula values seen in our older pa-
tients. However, other studies have demonstrated that
cystatin C has no advantages over creatinine in popula-
tion with GFR < 60 mL·min1·1.73 m2 [14]. Thus, the
severity of pre-existing renal disease should be consid-
ered when selecting the method to be used for the as-
sessment of renal function in older patients.
The use of ultrasound to measure residual bladder vo-
lume in order to obtain more precise two-hour urine vo-
lume estimates is essential in the elderly. In this popula-
tion, physiological disorders such as prostatic hypoplasia
and bladder prolapse can lead to underestimation of the
two-hour volume measured. Nonetheless, whether ad-
justed or not for residual bladder volume, CrCl-2h values
did not differ among our patients. An explanation for this
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finding is that few residual amounts cannot be easily de-
tected by ultrasound examination and this might have
influenced the interpretation of the results.
Diurnal variation in diuresis is another factor that has
been suggested to interfere with CrCl-2h assessment.
However, creatinine clearance estimates obtained at a
shorter interval (8 hours) have been demonstrated to be
as accurate as 24-h clearances [16].
In conclusion, two-hour creatinine clearance was not
an adequate substitute for GFR estimates based on crea-
tinine and cystatin C serum levels in older patients at
preoperative period. The ultrasonic assessment of resid-
ual bladder volume had no significant influence on the
calculation of two-hour creatinine clearance.
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