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Indian Pediatr 2017;54: 508-509 |
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Glomerular Filtration Rate Estimation by Serum
Creatinine or Serum Cystatin C in Preterm (<31 Weeks) Neonates
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*Parvesh Garg and Guillermo Hidalgo
Department of Pediatrics, University of Mississippi
Medical Center, Batson Children Hospital, Jackson, Mississippi, USA .
Email: [email protected]
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Glomerular filtration rate (GFR) was
estimated by serum creatinine (Schwartz's equation) and serum cystatin C
(Filler's equation) in preterm neonates (24-31 weeks of gestation) in a
prospective cohort study. Serum creatinine and cystatin C was obtained
at birth and then every two weeks during the first month. We found a
poor fit between two methods, and a steadier GFR assessment by cystatin
C.
Keywords: Acute kidney injury, Diagnosis,
Infants, Renal function tests.
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A ccurate measurement of glomerular filtration rate
(GFR) in preterm infants is difficult and frequently imprecise. Serum
creatinine (SCr) based GFR is erratic due to its tubular secretion and
reabsorption, changing muscle mass, bilirubin and fluid variations [1].
Serum Cystatin C is independent of muscle mass, bilirubin, age, sex,
weight, or diet, and can be used to estimate GFR [2]. Cystatin C has
been described as a better maker to estimate GFR than serum creatinine.
However, very few studies have been conducted in preterm neonates <31
weeks [3,4]. To help us guide clinical decisions, we aimed to determine
estimated GFR (GFR) by both methods.
This prospective cohort study was done at Vidant
medical center Greenville, North Carolina after Institutional Review
Board approval. We included neonates (24 to 31 weeks' gestational age)
within 48 h of birth. We excluded neonates with confirmed sepsis, renal
failure and prenatal congenital renal abnormalities. We estimated GFR at
48 hours of life, and on day 14 and day 28 of life. Cystatin C GFR was
estimated by Filler's equation [log GFR=1.962+ [1.123xlog (1/cystatin
C)], and creatinine based CGFR by schwartz equation [GFR=k × height/cr,
k=0.33] [5]. Serum Creatinine was IDMS traceable and Cystatin C was
measured by nephelometric immunoassay method using international
reference materials. Both methods were compared by Bland Altman plots.
Post-conceptional age was plotted against serum cystatin C- and
creatinine-based eGFR.
Serum creatinine and Cystatin C was measured in 37
samples taken from 14 infants mostly (12/14) delivered by
Caesarian-section. Out of 14 patients, 11 had received gentamicin for
suspected sepsis in first 48 hours, and all had respiratory distress
syndrome. Four patients had required dopamine for hypotension, and one
patient had received indomethacin for hemodynamically- significant
patient ductus arteriosus. Mean serum creatinine levels decreased
steadily (P=0.007), and mean eGFR using creatinine increased (P=0.001)
during first month (Table I, Web Fig. 1a). Mean
Serum cystatin C decreased from 1.39 mg/dL to 1.30 mg/dL (P=0.42). GFR
estimated by cystatin C was significantly higher, and did not show much
variability over time until the end of our observations (Web Fig.
1b,1c). The poor fit was seen in the Bland Altman plot with the mean
difference (Filler - Schwarz) around 25 with nearly all differences
greater than 25 when the mean of the two measure was 50 or less and
nearly all differences less than 25 when the mean was greater than 50 (Web
Fig. 1d).
TABLE I Serum Creatinine And Cystatin C Value And Corresponding Glomerular Filtration Rate
Parameter |
Day of Life
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0-2 |
14-16 |
28-30
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(n=14) |
(n=11) |
(n=7) |
Cystatin C (Mean) |
1.38 |
1.39 |
1.30 |
Cystatin C; Median (range) |
1.38 |
1.35
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1.34
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(1.27-1.48) |
(1.28-1.47) |
(1.25-1.36) |
GFR cystatin C
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64.4 |
64.3 |
68.7 |
Serum Creatinine (Mean )# |
0.63 |
0.43 |
0.29 |
Serum Creatinine (Median) |
0.62 |
0.41 |
0.21 |
GFR creatinine (Mean)# |
21.3 |
39.3 |
62.8 |
#P value significant (<0.05) between three
recordings.
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In our study, serum creatinine and serum cystatin C
levels decreased and eGFR increased with advanced postnatal age,
possibly due to renal maturation [6]. This study shows that in preterm
infants below 31 weeks, both methods for eGFR are poor fit to each
other. They are especially different between 24-27 weeks of post
conceptional age. This may, at least in part, be explained due to
placental transfer of creatinine.
The limitations of the study are small sample size,
influence of typical neonatal drugs and no gold standard measurement. As
shown in (Table I), infants had different degrees of
severity of illness that could have an impact on serum creatinine and
CysC levels. Currently, there is no international calibration for CysC.
In conclusion, this study shows that Cystatin C and
serum creatinine estimate GFR differently in preterm infants below 31
weeks.
References
1. Perrone RD, Madias NE, Levey AS. Serum creatinine
as an index of renal function: New insights into old concepts. Clin
Chem. 1992;38:1933-53.
2. Newman DJ. Cystatin C. Ann Clin Biochem.
2002;39:89-104.
3. Dharnidharka VR, Kwon C, Stevens G. Serum cystatin
C is superior to serum creatinine as a marker of kidney function: A
meta-analysis. Am J Kidney Dis. 2002;40:221-6.
4. Filler G, Grimmer J, Huang SH, Bariciak E.
Cystatin C for the assessment of GFR in neonates with congenital renal
anomalies. Nephrol Dial Transplant. 2012;27:3382-4.
5. Filler G, Huang SH, Yasin A. The usefulness of
cystatin C and related formulae in pediatrics. Clin Chem Lab Med.
2012;50:2081-91.
6. Bouvet Y, Bouissou F, Coulais Y, Seronie-Vivien S,
Tafani M, Decramer S, et al. GFR is better estimated by
considering both serum cystatin C and creatinine levels. Pediatr Nephrol.
2006;21:1299-306.
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