Full text of DOI:10.1177/147323000303100310

The Journal of International Medical Research
2003; 31: 231 – 235
Reference Values of Umbilical Cord
and Third-day Cystatin C Levels for
Determining Glomerular Filtration
Rates in Newborns
A BAHAR, Y YILMAZ, S UNVER, I GOCMEN AND F KARADEMIR
Department of Paediatrics, Gülhane Military Medical Academy Haydarpas¸a Training
Hospital, Istanbul, Turkey
The aim of this study was to determine
reference values for serum cystatin C at,
and 3 days after, birth, and to determine if
the concentration was influenced by
gender, gestational age or bilirubin level.
Umbilical cord and peripheral venous
blood was taken, and serum cystatin C,
creatinine, and total and direct bilirubin
levels were measured. The mean
concentration of cystatin C was not
significantly different between cord blood
and blood taken on day 3 (1.36 0.35 mg/l
and 1.35
0.33mg/l, respectively).
Comparison of subgroups, divided by
gender, duration of gestation and bilirubin
levels, using the Mann–Whitney U-test and
Wilcoxon analysis, showed no effect of
these parameters on cystatin C levels.
KEY WORDS: CYSTATIN C; NEWBORN; NEONATES; CORD BLOOD; HYPERBILIRUBINAEMIA
kidney, and readily passes through glomeruli
Introduction
due to its low molecular weight and positive
charge at physiological pH.3
Cysteine proteases are proteolytic enzymes
involved in many pathological processes
and found in the lysosomes of cells. Their
role is crucial in normal cellular metabolism,
being fundamental to intracellular protein
turnover, degradation of collagen, and
cleavage of precursor proteins. Cysteine
protease inhibitors, of which the cystatin
super-family is one example, constitute the
final regulatory step in the control of
cysteine proteases.1 Cystatin C, the most
studied cystatin, is present at high
concentrations in many body fluids
including seminal, cerebrospinal and
synovial fluids.2 It is excreted only by the
Measurement of creatinine clearance is
widely used for determining glomerular
filtration rate (GFR) in clinical practice.4,5
This method, however, takes a long time to
perform as it needs a 24-h urine collection.6,7
Cystatin C has been demonstrated to
reflect GFR better than other low molecular
weight proteins, including creatinine, with
sensitivity and specificity values of 70% and
100%, respectively.8,9 There are, however,
only a few studies reporting reference values
of this protein in umbilical cord or
peripheral blood samples obtained from
infants and children.5,10
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231

A Bahar, Y Yilmaz, S Unver et al.
Cystatin C levels and glomerular filtration rate
This study aimed to determine reference
Birth weight, gestational age, gender, and
whether the subject had significant hyper-
bilirubinaemia were recorded in each case.
Neonates with gestational ages < 37 weeks
and ≥ 37 weeks were deemed to be pre-term
and term, respectively.12 Hyperbilirubin-
aemia was defined as a serum total bilirubin
level of ≥ 2 mg/dl at birth, ≥ 8 mg/dl on
day 1, ≥ 12 mg/dl on day 2, ≥ 15 mg/dl on
day 3 and ≥ 17 mg/dl thereafter.13
values of cystatin C in umbilical cord and
peripheral venous blood taken from 3-day-old
neonates. These values were analysed in
different subgroups of neonates, comprising
gender (male or female), gestational age (pre-
term or term), and presence or absence of
significant hyperbilirubinaemia.
Patients and methods
PATIENTS
STATISTICAL ANALYSIS
The study was carried out on consecutive
babies, born to women followed antenatally at
the Department of Gynaecology and Obstetrics
of Gülhane Military Medical Academy
Haydarpas¸a Training Hospital, between June
2001 and July 2002. Written, informed consent
was given by the parents, and the local ethics
committee approved the study. Newborns
with any renal pathology, systemic illness,
congenital anomaly, conjugated hyper-
bilirubinaemia, or whose mothers had
chronic or pregnancy-induced hypertension,
pre-eclampsia/eclampsia, or any other
systemic illness were excluded from the study.
Serum cystatin C levels were analysed in the
total study group, and in subgroups with respect
to gender, gestational age and significant
hyperbilirubinaemia. The Mann–Whitney
U-test and Wilcoxon test were performed to
compare results between the subgroups.
Statistical significance was set at P < 0.05.
Results
Blood samples were taken from the
umbilical cord of 112 newborns (60 female
and 52 male) and from 98 (58 female and 40
male) 3-day-old neonates. Fourteen patients
did not attend for follow-up visits. The
demographic characteristics of the study
group are shown in Table 1.
METHODS
Blood samples were taken from the umbilical
cord at birth, and peripheral veins of the
same babies on the third day of life (day-3
samples). Samples were separated by
centrifugation at 1509.3 g for 5 min, within
6 h of collection, and serum was stored at
–20°C prior to the measurement of cystatin
C, and total and direct bilirubin levels.
The mean ( SD) level of cystatin C was
found to be 1.36 0.35 mg/l in cord blood
samples, and 1.35 0.33 mg/l in day-3 blood
samples, which was not significantly
different. The mean concentrations of
cystatin C in samples, subdivided according
to gender, gestational age and bilirubin
levels, are shown in Tables 2 – 4.
Bilirubin
was
measured
by
the
Jaundice was noted in 25 neonates on
day 3, and all had a direct bilirubin level of
< 0.5 mg/dl. The total bilirubin level, however,
was > 15 mg/dl in 12 of them.
Jendrassik–Grof method using a Beckman
Coulter Syncron LX-20 auto-analyser
(Fullerton, CA, USA).11 Cystatin C was
measured using
a
C
latex-enhanced
immunonephelometric assay (N Latex
Cystatin C kit; DADE Behring, Lederbach,
Germany), and a BN ProSpec® nephelometer
(DADE Behring, Lederbach, Germany).
Discussion
Cystatin
C is reported to give more
significant results than creatinine for the
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232

A Bahar, Y Yilmaz, S Unver et al.
Cystatin C levels and glomerular filtration rate
TABLE 1:
Demographic characteristics of the neonates entered into the study
Cord blood
112
3 days old
Total number of subjects
Female
98
60
58
Male
52
40
Body weight (g SD)
3240 530
3110 490
Pre-term (gestation age < 37 weeks)
Term (gestational age ≥ 37 weeks)
Serum total bilirubin (mg/dl)
Subjects with hyperbilirubinaemia
Subjects without hyperbilirubinaemia
14
98
14
84
1.1 0.6
5
7.6 4.0a
12
107
86
aIncludes 12 patients with hyperbilirubinaemia and total bilirubin > 15 mg/dl.
TABLE 2:
Comparison of cystatin C levels (mg/l) with respect to gender
Male mean SD
(range)
Female mean SD
(range)
P-valuea
Cord blood
3 days old
1.38 0.19
(0.77 – 2.43)
1.34 0.39
(0.78 – 2.30)
0.48
1.34 0.34
(0.69 – 2.2)
1.35 0.32
(0.86 – 2.40)
0.37
aP < 0.05 was taken to be significant.
TABLE 3:
Comparison of cystatin C levels (mg/l) with respect to gestational age
Pre-terma mean SD
(range)
Terma mean SD
(range)
P-valueb
Cord blood
3 days old
1.40 0.18
(1.30 – 1.66)
1.35 0.37
(0.69 – 2.43)
0.32
1.49 0.35
1.32 0.32
0.20
(0.98 – 2.30)
(0.78 – 2.40)
aPre-term was defined as gestational age < 37 weeks while term babies had a gestational age ≥ 37 weeks.
bP < 0.05 was taken to be significant.
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233

A Bahar, Y Yilmaz, S Unver et al.
Cystatin C levels and glomerular filtration rate
TABLE 4:
Comparison of cystatin C levels (mg/l) with respect to hyperbilirubinaemia
With hyperbilirubinaemia
Without hyperbilirubinaemia
P-valuea
Cord blood
3 days old
1.39 0.23
(0.97 – 1.78)
1.36 0.37
(0.69 – 2.43)
0.16
1.37 0.30
1.33 0.33
0.12
(0.83 – 2.92)
(0.78 – 2.40)
aP < 0.05 was taken to be significant.
assessment of renal function in patients with
renal disease.3,14 – 16 Herget-Rosenthal et al.17
reported that, in determining decreased GFR,
cystatin C provided a sensitivity of 97% and
a specificity of 96%, whereas creatinine
provided rates of 83% and 87%, respectively.
Beta-2 and alpha-1 microglobulin are
inferior to creatinine in assessing GFR.16
finding that the cystatin C reference range for
neonates is higher than for adults supports
the view that cystatin C levels reflect the
maturation of GFR.9,19 There was no marked
difference between the birth weights of our
pre-term and term newborns, suggesting,
along with other studies, that birth weight
has no effect on cystatin C levels.5,19
Bökenkamp et al.19 reported that cystatin
C levels showed a mild increase in patients
with hyperbilirubinaemia, but other studies
have demonstrated that cystatin C is not
influenced by levels of bilirubin.5,18 We found
no significant difference between levels of
cystatin C in newborns or neonates, with
and without hyperbilirubinaemia, a finding
consistent with previous studies.5,18,19 Our
results are also consistent with previous
studies with regard to cystatin C levels and
gender.2,5,9,10,19
Increased cystatin C levels have been
reported in neonates, but it has been
suggested that the increase is not derived
from the mother, and there is no correlation
between the levels of cystatin C in mother
and baby.18 We found no significant
difference between levels of cystatin C in cord
blood and day-3 venous blood, supporting
the idea that the production and metabolism
of cystatin C are independent in the fetus and
mother. The elevated levels seen in the first
few days rapidly decrease, and by 4 months
are within a reference range of 0.7 –
1.38 mg/l.5,19 We found mean cystatin C
levels in the cord blood samples, and day-3
venous blood samples, to be near the upper
limit of this previously reported reference
range. Our results are therefore consistent
with previous studies, and suggest no
significant difference between levels of
cystatin C in cord blood and day-3 venous
blood samples. Premature infants are
reported to have the highest levels of cystatin
C, and it is suggested that the decrease in
levels during the early years of life is an
indicator for the maturation of GFR.5 Our
In conclusion, the levels of serum cystatin
C in cord or day-3 blood samples, did not
differ significantly when compared as a total
group, or divided into subgroups according
to gender, gestational age or presence or
absence of hyperbilirubinaemia. Cystatin C
is regarded as an alternative to creatinine for
assessing GFR, but it is not yet accepted as
being superior to creatinine. A limited
number of studies on the reference values of
cystatin C in children are available, so
further studies with large numbers of cases
are required to assess whether cystatin C
should replace creatinine as a test for GFR.
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234

A Bahar, Y Yilmaz, S Unver et al.
Cystatin C levels and glomerular filtration rate
• Received for publication 4 January 2003 • Accepted 6 February 2003
Copyright © 2003 Cambridge Medical Publications
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Address for correspondence
Dr A Bahar
GATA Haydarpas¸a Eg˘itim Hst, Çocuk Servisi 81327, Üsküdar-Istanbul, Turkey.
E-mail: arbahar@hotmail.com
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