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| ORIGINAL ARTICLE |
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| Year : 2020 | Volume
: 3
| Issue : 1 | Page : 10-14 |
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Cystatin C as a biomarker of acute kidney injury in sick neonates
Jyoti Bagla, Sweta Kumari, Raksha Gupta, Iqra Khan
Department of Pediatrics, ESI PGIMSR, Basaidarapur, Delhi, India
| Date of Submission | 02-Dec-2019 |
| Date of Decision | 15-Mar-2020 |
| Date of Acceptance | 01-Apr-2020 |
| Date of Web Publication | 27-Jun-2020 |
Correspondence Address:
Sweta Kumari
Department of Pediatrics, ESI PGIMSR, Basaidarapur, Delhi - 110 015
India
 Source of Support: None, Conflict of Interest: None  | 7 |
DOI: 10.4103/AJPN.AJPN_29_19
Objective: This study was planned to study serum cystatin C (CysC) levels in sick neonates admitted in neonatal intensive care unit (NICU) with predisposing risk factor(s) for development of acute kidney injury (AKI). We evaluated serum levels of CysC and creatinine in sick neonates. Methods: Ninety-four sick neonates with prematurity, sepsis, respiratory distress, and/or perinatal asphyxia requiring NICU admission were enrolled. Serum levels of creatinine and CysC were measured on day 3 of life. Results: Serum levels of both cystatin C and creatinine were significantly elevated in neonates who developed AKI versus those who did not (CysC: 2.18 ± 0.59 vs. 1.91 ± 0.47 mg/dl, P = 0.04; creatinine: 1.68 ± 0.75 vs. 0.89 ± 0.40, P < 0.001). Levels of CysC were elevated in sick neonates with risk factors of developing AKI. Conclusions: Serum levels of CysC are elevated in sick neonates at risk of AKI. CysC is a useful indicator of risk of AKI in ill neonates.
Keywords: Acute kidney injury, biomarker, serum creatinine, serum cystatin C, sick neonates
How to cite this article:
Bagla J, Kumari S, Gupta R, Khan I. Cystatin C as a biomarker of acute kidney injury in sick neonates. Asian J Pediatr Nephrol 2020;3:10-4 |
| Introduction | |  |
Acute kidney injury (AKI) is characterized by the sudden onset of renal dysfunction, leading to impaired control of acid–base, electrolyte, and fluid balance. Critically ill neonates are at a high risk of developing AKI due to exposure to perinatal anoxia or hypoxia and nephrotoxic medications and frequent infections, leading to multiorgan failure.[1],[2] The incidence of AKI in critically ill neonates is estimated at 8%–24% and is associated with mortality in 10%–61% cases.[3],[4] AKI is independently linked to mortality [1] and is associated with long-term consequences among the survivors.[5] The incidence of AKI in neonates varies by definition and classification criteria,[2] treatment strategies remain suboptimal, and diagnosis is usually delayed.[6] Serum creatinine-based identification of AKI is not satisfactory, for the following reasons: creatinine measures function rather than indicate injury;[2] serum creatinine level is unchanged until the kidneys lose 25%–50% of their function; serum creatinine level depends on muscle mass, hydration, sex, age, medications, and endogenous substances such as bilirubin; creatinine is secreted by tubules and serum levels underestimate glomerular filtration rate (GFR); in the first 48 h of life, serum creatinine reflects maternal kidney function; and creatinine levels vary significantly by gestational maturity.[7],[8]
Since traditional markers of AKI lack sensitivity and specificity for early diagnosis in neonates, the role of other biomarkers in enabling a timely diagnosis of AKI is being explored. By reducing the time to diagnosis, such a biomarker could potentially prevent secondary injury, through dose adjustments or avoidance of nephrotoxic drugs and intravenous contrast agents, and/or enable early intervention, such as appropriate fluid management, and timely initiation of renal replacement therapy, thus improving outcomes.[9],[10],[11] Serum cystatin C (CysC) has been proposed as such a biomarker. This cysteine protease inhibitor is synthesized by all nucleated cells and is released into the blood at a relatively constant rate. It is freely filtered by the glomerulus, completely reabsorbed by the proximal tubules and not secreted.[12] In newborns, CysC levels are independent of gender, height, gestational age, lean body mass, and serum bilirubin level,[13] all of which interfere with estimates based on serum creatinine. Unlike serum creatinine, fetal CysC levels do not relate to maternal CysC levels.[14] Since CysC appears to avoid many of the problems associated with serum creatinine as an estimate of renal function in neonates, it might be superior to the former in estimating GFR and detecting AKI in this population. While CysC is reported to be more useful than creatinine in detecting AKI in critically ill children and adults [15],[16],[17],[18],[19] its role has not been validated in neonates. This study was planned to compare levels of CysC and creatinine in indicating AKI in sick neonates admitted to a level III neonatal intensive care unit (NICU), and to determine the risk factors for AKI in this population.
| Methods | | |
This prospective observational study was carried out in the NICU of a tertiary care teaching hospital in New Delhi. The study, approved by the Institutional Ethical Clearance Committee, aimed to examine CysC levels in sick neonates and the risk factors predisposing to development of AKI. All intramural neonates admitted to NICU who were at risk of AKI, with risk factors, such as sepsis, perinatal asphyxia, neonatal encephalopathy, and respiratory distress, were enrolled after taking written and informed consent from parents or legal guardian.
Standard case definition was used to assess eligibility. Sepsis was defined as probable, if based on laboratory parameters alone, and confirmed, if it was culture-proven. Respiratory distress syndrome was diagnosed in the presence of clinical features of respiratory distress and need for supplemental oxygen for more than 6 h or any positive airway pressure support. Perinatal asphyxia was defined by need for resuscitation with more than 1 min of positive pressure ventilation with cord blood gas <7.0 and base excess of <−16. Neonatal encephalopathy was defined as per modified Sarnat and Sarnat criteria. Exclusion criteria were lack of informed consent, or exchange transfusion or death before day 3 of life. Patients with antenatally or postnatally confirmed anomaly of urinary tract were not excluded.
AKI on day 3 was defined by pediatric risk, injury, failure, loss, and end-stage (pRIFLE) criteria modified for newborns, as follows: Risk: an increase in creatinine to >1.5–2 times, or decrease in GFR by >25% to 50%, from baseline, or fall in urine output to <1.5 ml/kg/hr for 24 h; Injury: an increase in creatinine to >2–3 times, or decrease in GFR to >50%–75%, from baseline, or fall in urine output to <1 ml/kg/hr for 24 h; and Failure: an increase in creatinine to >3 times, or decrease in GFR to >75% from baseline, or fall in urine output to <0.7 ml/kg/hr for 24 h.
Detailed history and examination were recorded on a predesigned pro forma. Urine output was measured by urinary catheterization or diaper weighing, based on the clinician's discretion. Serum levels of creatinine and CysC were estimated at 72 h of birth. For patients with AKI, the assays were repeated every 48 h until recovery. Creatinine and CysC were estimated using modified Jaffe method and nephelometry, respectively. Briefly, CysC in the sample binds to the specific polyclonal rabbit anti-CysC antibody that has been adsorbed on to latex particles, leading to agglutination. Which is measured, and levels extrapolated based on a calibration curve prepared from serial dilutions of a known standard concentration of CysC.
Statistical analysis
Based on data distribution, continuous variables were expressed as mean with standard deviation or median with interquartile range. Categorical data are provided as proportions and frequencies. Comparisons were made using independent t-test or Mann Whitney U-test for continuous variables and Chi-square test for categorical data; P < 0.05 was considered statistically significant. Receiver operating characteristic (ROC) curves were used to detect the threshold value of CysC and serum creatinine that had the best combination of sensitivity and specificity. Pearson correlation coefficients were used to examine the association between CysC and serum creatinine. Statistical analysis was carried out with the statistical package SPSS for Mac (IBM Corp Inc., version 22.0, 2013; Armonk, NY, USA).
Sample size calculation
The sample size, estimated to detect an expected correlation of 0.5 between CysC and creatinine as biomarkers of AKI, at 80% power and using an alpha error of 5%, was calculated as 29 neonates with AKI. Since AKI affects approximately 35% of sick newborns, we required to enroll 83 sick newborns. Expecting 10% mortality or dropout by day 3 of life, we planned to enroll 93 sick neonates. Due to financial constraints in testing samples from prospectively enrolled healthy newborns, historical controls (normal neonates were used.[20]
| Results | | |
Of 122 neonates admitted to NICU and screened for eligibility during June–November 2016, 94 neonates were enrolled, as depicted in the STROBE flow chart [Figure 1]. [Table 1] shows the baseline characteristics of the enrolled subjects. Most neonates were born at late preterm or term gestation. Eighteen (19.1%) neonates developed AKI. There were no significant differences in rates of sepsis, respiratory distress, or encephalopathy between patients with or without AKI. There was bimodal distribution of AKI rate as per gestation; AKI was seen in 21.7% and 24.3% patients with gestation age of <32 weeks and 37–42 weeks, respectively, and in 11.7% neonates with gestation of 33–36 completed weeks. | Table 1: Baseline characteristics of patients with and without acute kidney injury (AKI)
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[Table 2] shows that serum levels of both CysC and creatinine were elevated at baseline in patients with AKI (CysC 2.18 ± 0.59 vs. 1.91 ± 0.47, P = 0.041; creatinine 1.68 ± 0.75 vs. 0.89 ± 0.40, P < 0.001). When compared to historical controls, CysC levels were significantly higher among sick neonates with risk factors of developing AKI [Table 3].[20] | Table 2: Comparison of serum cystatin C and creatinine levels among acute kidney injury and nonacute kidney injury group with risk factors
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 | Table 3: Comparison of serum cystatin C levels among cases and historic controls
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[Figure 2] shows that CysC correlated positively serum creatinine (coefficient = 0.34, P = 0.001). The area under the ROC curve for CysC was 0.65 (95% CI: 0.50–0.80; P = 0.055) and for serum creatinine was 0.83 (95% CI: 0.72–0.94; P < 0.001). Optimal threshold value in detection of AKI for CysC was 2.36 mg/dl (sensitivity 45%; specificity 88%) and for serum creatinine was 1.25 mg/dl (sensitivity 66%; specificity 84%). | Figure 2: Receiver operating characteristic curve analysis for serum cystatin C and serum creatinine levels in predicting the development of acute kidney injury
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| Discussion | | |
This prospective observational study was planned with the intent to determine the diagnostic utility of CysC in predicting AKI. AKI was seen in about one-fifth of critically ill newborns, comparable to reported rates of 6%–24% in sick neonates.[21],[22] Jetton et al. also reported similar observation in a multicenter observational study.[21] Sepsis, respiratory distress, neonatal encephalopathy, or prematurity were not associated with AKI. Both CysC and creatinine were significantly higher in subjects with AKI.
Previous reports indicate that CysC is increased in neonates with AKI, with or without risk factors such as respiratory distress, perinatal asphyxia, and cardiopulmonary bypass.[23],[24] Further, CysC might be elevated in preterm neonates, irrespective of the presence of AKI, possibly due to mild tubulointerstitial injury not manifesting as AKI. Elmas et al. did not find statistically significant differences in urinary levels of CysC between non-septic, non-asphyxiated, critically ill preterm neonates with or without AKI.[24] In the present study, CysC levels did not differ between neonates with perinatal asphyxia with or without AKI, consistent with reports by Sarafidis et al., and Treiber et al.,[20],[23] and correlated positively with serum creatinine, in concordance with the observations in another prospective observational study.[25] There was no significant correlation between CysC and birth weight or gestation. These findings support a role for CysC as a robust marker of glomerular filtration. The finding of CysC levels being significantly elevated among neonates with risk factors for AKI (prematurity, sepsis, asphyxia encephalopathy, and respiratory distress) as compared to historical control of healthy neonates [20] indicates that CysC might detect subtle renal injury not manifesting as AKI as defined by conventional markers such as serum creatinine, and could serve as a useful alert to clinicians caring for such neonates.
The strength of our study is its large sample size of neonates with adequate representation of various risk factors predisposing to AKI. In addition, this was a prospective observational study and utilized both creatinine and urine output criteria to define AKI. However, there are several limitations. First, the definition of AKI, based on the increase in serum creatinine is likely to be flawed, for reasons stated previously.[26] Second, our study did not incorporate follow-up information on the enrolled newborns, which could have improved our understanding of the progression and outcomes of AKI. Third, both serum creatinine and CysC were assessed usually once. Fourth, we could not enroll a parallel control group of relatively healthy newborns and relied on historical control data.[20] Finally, we did not study any additional serum or urinary biomarkers to compare their relative utility vis-à-vis CysC. Further studies with larger sample size, an appropriate control limb, a sequential sampling strategy and adequate follow-up, are required to establish the role of CysC in detecting AKI compared to serum creatinine.
| Conclusions | | |
Serum levels of both CysC and creatinine are elevated in sick neonates with AKI. CysC levels are elevated in sick compared to healthy neonates even in the absence of AKI, perhaps indicating mild renal injury.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]
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