Diagnostic accuracy of cystatin C compared to serum creatinine for the estimation of renal dysfunction in adults and children--a meta-analysis

Normalization of glomerular filtration rate in obese children

BACKGROUND

Glomerular filtration rate (GFR) is conventionally indexed to body surface area (BSA), but this may lead to biased results when applied to subjects of abnormal body size. The aim of our study was to examine the impact of normalization to the BSA and alternative body size descriptors on measured and estimated GFR in overweight and obese children.

METHODS

This was a cross-sectional study of 313 children aged 8-9 years old. GFR was measured by 24-h creatinine clearance (CrCl) and additionally estimated from serum creatinine and cystatin C (CysC) using the combined Zappitelli formula, both as absolute values and adjusted to various body size descriptors. The results were compared between 163 normal-weight, 89 overweight and 61 obese children.

RESULTS

Compared to the normal-weight children, mean absolute GFR (both measured and estimated) was higher in the overweight and obese children, whereas BSA-adjusted GFR was lower. Linear regression models fitted in normal-weight children revealed equally close associations between absolute GFR and squared height, ideal body weight (IBW) and BSA derived from IBW. Normalization of GFR to the IBW-derived BSA completely eliminated the discrepancy between absolute and BSA-indexed GFR in overweight and obese children.

CONCLUSIONS

Indexing of GFR to BSA calculated from the ideal-rather than actual-body weight is a promising approach to avoid overcorrection when studying obese children. Further studies should assess the accuracy of this approach across the full range of age and BMI distribution.

Serum and urinary cystatin C in cats with feline immunodeficiency virus infection and cats with hyperthyroidism

OBJECTIVES

The objective of this study was to investigate serum cystatin C (sCysC) and urinary cystatin C (uCysC) in cats with hyperthyroidism and cats with feline immunodeficiency virus (FIV).

METHODS

Thirty cats with FIV, 26 hyperthyroid cats and 28 healthy cats were included. sCysC and uCysC:creatinine (uCysC/uCr) ratio were measured with a human particle-enhanced nephelometric immunoassay, previously validated for feline CysC measurement. Routine renal variables (serum creatinine [sCr], urine specific gravity, urinary protein:creatinine ratio [UPC]) were also measured in the three groups.

RESULTS

Cats with hyperthyroidism had significantly higher sCysC and higher uCysC/uCr ratio, lower sCr and a higher UPC than healthy cats. Cats with FIV infection did not show a significantly higher sCysC concentration but had a significantly higher sCr and UPC than healthy cats. uCysC could be detected in only four of them.

CONCLUSIONS AND RELEVANCE

This study demonstrated that sCysC is increased in cats with hyperthyroidism, in contrast with sCr, but not in cats with FIV. Many hyperthyroid cats, but only four cats with FIV, had an elevated uCysC/uCr ratio. Further studies may reveal if uCysC might be a valuable marker for tubular dysfunction in cats.

Are low birth weight neonates at risk for suboptimal renal growth and function during infancy?

Background

To assess the renal growth and function of neonates during infancy in relation to birth weight and gestational age.

Methods

A longitudinal study was conducted at a tertiary hospital in South India from June 2010 to August 2014. Low birth weight neonates (LBW) were further sub-classified based on gestational age and compared with normal birth weight (NBW) full term neonates at birth, 6 months and 18-24months of age. The renal volume was measured by ultrasound and renal function by Cystatin C- derived glomerular filtration rate (CysGFR) at the three time points during the dynamic phase of renal maturation in infancy.

Results

We recruited 100 LBW and 66 NBW term neonates. Thirty five percent of the LBW neonates were SGA. Among the AGA neonates, 39 % were LBW neonates. The mean height and weight of the LBW neonates were significantly lower compared to NBW neonates throughout infancy. The increment in kidney volume was in accordance with the change in body size, being lower in LBW compared to NBW infants. The combined kidney volume was significantly lower in LBW and SGA neonates across all three time points (p < 0.001). CysGFR in the LBW and SGA infants, despite having low kidney volumes, were comparable to the GFRs of NBW and AGA neonates at the end of infancy.

Conclusion

This study highlights the fact that both birth weight and gestational age influence kidney growth and function in infancy. At the end of infancy, despite a significant difference in kidney volumes and age at last follow up, the glomerular filtration rate was comparable between LBW and NBW infants. Though not statistically significant, there was a trend towards higher urine microalbumin in LBW compared to NBW in infancy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-016-0314-7) contains supplementary material, which is available to authorized users.

Correlation between cystatin C-based formulas, Schwartz formula and urinary creatinine clearance for glomerular filtration rate estimation in children with kidney disease

INTRODUCTION

Assessment of glomerular filtration rate (GFR) is an important tool for monitoring renal function.

OBJECTIVES

Regarding to limitations in available methods, we intended to calculate GFR by cystatin C (Cys C) based formulas and determine correlation rate of them with current methods.

PATIENTS AND METHODS

We studied 72 children (38 boys and 34 girls) with renal disorders. The 24 hour urinary creatinine (Cr) clearance was the gold standard method. GFR was measured with Schwartz formula and Cys C-based formulas (Grubb, Hoek, Larsson and Simple). Then correlation rates of these formulas were determined.

RESULTS

Using Pearson correlation coefficient, a significant positive correlation between all formulas and the standard method was seen (R(2) for Schwartz, Hoek, Larsson, Grubb and Simple formula was 0.639, 0.722, 0.705, 0.712, 0.722, respectively) (P<0.001). Cys C-based formulas could predict the variance of standard method results with high power. These formulas had correlation with Schwarz formula by R(2) 0.62-0.65 (intermediate correlation). Using linear regression and constant (y-intercept), it revealed that Larsson, Hoek and Grubb formulas can estimate GFR amounts with no statistical difference compared with standard method; but Schwartz and Simple formulas overestimate GFR.

CONCLUSION

This study shows that Cys C-based formulas have strong relationship with 24 hour urinary Cr clearance. Hence, they can determine GFR in children with kidney injury, easier and with enough accuracy. It helps the physician to diagnosis of renal disease in early stages and improves the prognosis.

Diabetic kidney disease: a role for advanced glycation end-product receptor 1 (AGE-R1)?

Diabetic patients are postulated to be in a perpetual state of oxidative stress and inflammation at sites where chronic complications occur. The accumulation of AGEs derived from both endogenous and exogenous sources (such as the diet) have been implicated in the development and progression of diabetic complications, particularly nephropathy. There has been some interest in investigating the potential for reducing the AGE burden in chronic disease, through the action of AGE "clearance" receptors, such as the advanced glycation end-product receptor 1 (AGE-R1). Reducing the burden of AGEs has been linked to attenuation of inflammation, slower progression of diabetic complications (in particular vascular and renal complications) and has been shown to extend lifespan. To date, however, there have been no direct investigations into whether AGE-R1 has any role in modulating normal kidney function, or specifically during the development and progression of diabetes. This mini-review will focus on the recent advances in knowledge around the mechanistic function of AGE-R1 and the implications of this for the pathogenesis of diabetic kidney disease.

A model-based analysis of the predictive performance of different renal function markers for cefepime clearance in the ICU

OBJECTIVES

Several population pharmacokinetic models for cefepime in critically ill patients have been described, which all indicate that variability in renal clearance is the main determinant of the observed variability in exposure. The main objective of this study was to determine which renal marker best predicts cefepime clearance.

METHODS

A pharmacokinetic model was developed using NONMEM based on 208 plasma and 51 urine samples from 20 ICU patients during a median follow-up of 3 days. Four serum-based kidney markers (creatinine, cystatin C, urea and uromodulin) and two urinary markers [measured creatinine clearance (CLCR) and kidney injury molecule-1] were evaluated as covariates in the model.

RESULTS

A two-compartment model incorporating a renal and non-renal clearance component along with an additional term describing haemodialysis clearance provided an adequate description of the data. The Cockcroft-Gault formula was the best predictor for renal cefepime clearance. Compared with the base model without covariates, the objective function value decreased from 1971.7 to 1948.1, the median absolute prediction error from 42.4% to 29.9% and the between-subject variability in renal cefepime clearance from 135% to 50%. Other creatinine- and cystatin C-based formulae and measured CLCR performed similarly. Monte Carlo simulations using the Sanford guide dose recommendations indicated an insufficient dose reduction in patients with a decreased kidney function, leading to potentially toxic levels.

CONCLUSIONS

The Cockcroft-Gault formula was the best predictor for cefepime clearance in critically ill patients, although other creatinine- and cystatin C-based formulae and measured CLCR performed similarly.

Importance of cystatin C and uric acid levels in the association of cardiometabolic risk factors in Japanese junior high school students

BACKGROUND

Serum cystatin C (CysC), a novel marker of renal function, is associated with the components of metabolic syndrome in adults. Little is known about the utility of CysC and its association with cardiometabolic risks in young subjects.

METHODS AND RESULTS

In a cohort of 454 Japanese junior high school students, the distribution of serum CysC levels and associated variables were analyzed. CysC levels were significantly higher in boys than in girls (0.92±0.10mg/L vs. 0.77±0.08mg/L, p<0.001). CysC was significantly correlated with serum creatinine (r=0.473, p<0.001), and serum uric acid (SUA) (r=0.546, p<0.001). Multivariable regression analysis revealed significant associations between CysC and SUA in all subjects (β=0.241, p<0.001), and in boys and girls separately (β=0.264 and 0.240, respectively, both p<0.001). Importantly, subjects with elevation of both serum CysC and SUA levels had the highest ratio of triglyceride to high-density lipoprotein cholesterol.

CONCLUSIONS

CysC had significant associations with both creatinine and SUA in Japanese junior high school students. The concomitant elevation of serum CysC and SUA levels was associated with subclinical lipid metabolism dysregulation, and suggested the presence of cardiometabolic risk accumulation.

Practice recommendations for the monitoring of renal function in pediatric non-renal organ transplant recipients

The management of non-renal pediatric solid organ transplant recipients has become complex over the last decade with innovations in immunosuppression and surgical techniques. Post-transplantation follow-up is essential to ensure that children have functioning allografts for as long as possible. CKD is highly prevalent in these patients, often under recognized, and has a profound impact on patient survival. These practice recommendations focus on the early detection and management of hypertension, proteinuria, and renal dysfunction in non-renal pediatric solid organ transplant recipients. We present seven practice recommendations. Renal function should be monitored regularly in organ transplant recipients, utilizing assessment of serum creatinine and cystatin C. GFR should be calculated using the new Schwartz formula. Transplant physicians should also monitor blood pressure using automated oscillometric devices and confirm repeated abnormal measures with manual blood pressure readings and ambulatory 24-h blood pressure monitoring. Proteinuria and microalbuminuria should also be assessed regularly. Referrals to a pediatric nephrologist should be made for non-renal organ transplant recipients with repeated blood pressures >95th percentile using the Fourth Task Force reference intervals, microalbumin/creatinine ratio >32.5 mg/g (3.7 mg/mmol) creatinine on repeated testing and/or GFR <90 mL/min/1.73 m(2) .

Performance of the creatinine and cystatin C-based equations for estimation of GFR in Chinese patients with chronic kidney disease

BACKGROUND

Currently, creatinine- or cystatin C-based glomerular filtration rate (GFR) estimation equation has been recommended to assess GFR in CKD patients. However, it is still obscure whether those equations performed consistently outstandingly in Chinese population.

METHODS

The equations were validated in a population totaling 632 participants (mean age 61.6 ± 12.3 years). The estimated GFR (eGFR) calculated separately by six equations (C-MDRD, C_cys, C_scr-cys, CKD-EPI_scr, CKD-EPI_cys, and CKD-EPI_scr-cys equations) was compared with the reference GFR (rGFR) measured by the ^99mTc-DTPA renal dynamic imaging method. Participants were divided into age and rGFR specific subgroups.

RESULTS

CKD-EPI_scr-cys equation had a larger area under receiver operating characteristic curve (ROC^AUC) and relative higher sensitivity (79.8 %) and specificity (93 %) to diagnose CKD. CKD-EPI_scr-cys and CKD-EPI_cys equations appeared to be more accurate with higher proportion of eGFR within 30 % of rGFR (P ₃₀) value. Those two equations performed as well in older people as in the younger population. The CKD-EPI_scr-cys equation acquired the highest P ₃₀ (80.9 %) in subgroups with rGFR ≥60 mL/min/1.73 m², while the CKD-EPI_cys equation yielded the best performance in the rGFR <60 mL/min/1.73 m² subgroup.

CONCLUSION

CKD-EPI_scr-cys formula had better capability to accurately evaluate GFR in the participants CKD stages 1-2 in Chinese ethnic. The application of the cystatin C-based equations may be the optimal one for patients of moderately to severely injured GFR. Considering the accuracy in the entire range of participants less ideally, the additional of the Chinese racial factor is assumed to be essential.

Modification of the Schwartz equations for children increases their accuracy at eGFR > 60 mL/min/1.73 m(2)

AIM

Estimation of eGFR in children with normal kidney function using the Schwartz equations results in underestimating real GFR.

MATERIALS AND METHODS

We propose modification of three Schwartz equations - two based on creatinine concentration (eGFRScrBS bedside) and (eGFRScr) and one 3-marker based on creatinine, urea and cystatin C concentrations (eGFRS3M). The iohexol test (reference method) was performed 417 times in 353 children >2 years with mean GFR: 98 ± 31.6 ml/min/1.73m(2). The assessment included also the Filler and Zappitelli equations. The modification was performed using methods: (1) based on equation, eGFRcor = a [eGFR - T] + T, where T = 50, if eGFR > T, and a equals for: eGFRScrBS 1.4043, for eGFRScr 2.0048, for eGFRS3M 1.2951, and (2) based on correction of all coefficients of the original equation.

RESULTS

For comparison of all the results and for children with GFR< 60, 60-90, 90-135 and > 135 ml/min/1.73m(2) the correlation coefficient, relative error (RE) and root mean square relative error (RMSRE) was employed and revealed improvement of RE from 25.9 to 6.8 and 3.9% (depending on the correction method) for eGFRScr; from 19 to 8.1 and 3.9% for eGFRScrBS and: from 11.6% to 2.0 and 2.3% for eGFRS3M (respectively). The RMSRE values changed from 30 to 21.3 and 19.8% for eGFRScr, from 25.1 to 21.6 and 19.8% for eGFRScrBS and from 19.1 to 15.8 and 15.3 % for eGFRS3M.

CONCLUSIONS

Modifications of Schwartz equations at GFR > 60 ml/min/1.73m(2) significantly improves the accuracy of calculating eGFR. The 3-markers equation is more accurate and should be employed frequently.

Assessment of glomerular filtration rate in the neonate: is creatinine the best tool?

PURPOSE OF REVIEW

This article answers the question of whether creatinine is the best biomarker for monitoring neonatal glomerular filtration rate (GFR) in view of recent advances in measuring neonatal renal function.

RECENT FINDINGS

We rely largely on serum creatinine for the estimation of GFR in the newborn, even though creatinine is freely exchanged through the placenta. During the first few days of life, the serum creatinine reflects maternal renal function or the maternal creatinine. Back filtration of creatinine in preterm newborns is also a serious limitation. This review summarizes current knowledge on the prenatal and postnatal handling of creatinine as well as that of other, more novel biomarkers of GFR, such as cystatin C (CysC) and β-trace protein (BTP). Only small amounts of CysC cross the placenta, whereas BTP does not cross the placenta at all. However, BTP measurements are not widely available. Recent studies on renal volumetry are also discussed.

SUMMARY

Currently, CysC may be the most suitable marker of neonatal renal function, but its availability is still limited, it is more costly, and the best method of reporting acute kidney injury and neonatal estimated GFR remains to be established.

Correlation of cystatin C and creatinine based estimates of renal function in children with hydronephrosis

INTRODUCTION

The use of a simple and accurate glomerular filtration rate (GFR) estimating method aiming minute assessment of renal function can be of great clinical importance.

OBJECTIVES

This study aimed to determine the association of a GFR estimating by equation that includes only cystatin C (Gentian equation) to equation that include only creatinine (Schwartz equation) among children.

PATIENTS AND METHODS

A total of 31 children aged from 1 day to 5 years with the final diagnosis of unilateral or bilateral hydronephrosis referred to Besat hospital in Hamadan, between March 2010 and February 2011 were consecutively enrolled. Schwartz and Gentian equations were employed to determine GFR based on plasma creatinine and cystatin C levels, respectively.

RESULTS

The proportion of GFR based on Schwartz equation was 70.19± 24.86 ml/min/1.73 m(2), while the level of this parameter based on Gentian method and using cystatin C was 86.97 ± 21.57 ml/min/1.73 m(2). The Pearson correlation coefficient analysis showed a strong direct association between the two levels of GFR measured by Schwartz equation based on serum creatinine level and Gentian method and using cystatin C (r = 0.594, P < 0.001). The linear association between GFR values measured with the two methods included cystatin C based GFR = 50.8+ 0.515 × Schwartz GFR. The correlation between GFR values measured by using serum creatinine and serum cystatin C measurements remained meaningful even after adjustment for patients' gender and age (r = 0.724, P < 0.001).

CONCLUSION

The equation developed based on cystatin C level is comparable with another equation, based on serum creatinine (Schwartz formula) to estimate GFR in children.

Relationship between High Serum Cystatin C Levels and the Risk of Gestational Diabetes Mellitus

Aims

Serum cystatin C (CysC) has recently been shown to be associated with the incidence of type 2 diabetes mellitus (T2DM) and progression to the pre-diabetic state. The aim of this study was to explore the relationship between serum CysC and the risk of gestational diabetes mellitus (GDM) in Chinese pregnant women.

Methods

This cross-sectional study consisted of 400 pregnant women including111 with GDM and 289 with normal glucose tolerance at 24–28 weeks of gestation. The subjects were further divided into four groups according to the CysC quartiles, and their clinical characteristics were compared. The serum CysC concentration was measured using immunoturbidimetry and the degree of insulin resistance was assessed by the homeostasis model assessment of insulin resistance (HOMA-IR).

Results

Serum CysC levels were significantly higher in pregnant women with GDM than in the healthy pregnant women[1.0(0.8–1.8) vs 0.7(0.6–1.0), P<0.01). The Spearman’s correlation analysis showed that serum CysC was positively associated with HOMA-IR(r = 0.118, P<0.05) and the occurrence of GDM(r = 0.348, P<0.01). The pregnant women were divided into quartiles according to their serum CysC concentrations. Compared to the first quartile, pregnant women in Q2 (OR, 2.441; P = 0.025), Q3 (OR, 3.383; P = 0.001) and Q4 (OR, 5.516; P<0.001) had higher risk of GDM after adjusted for age, BMI, HbA1c and HOMA-IR. Further, with a rise in the serum CysC, there was an increasing trend in the HOMA-IR levels (P<0.05). A binary logistic regression analysis after adjusting for other confounding variables revealed a significant and independent association between serum CysC and GDM [OR = 14.269; 95% confidence interval, 4.977–40.908, P<0.01].The receiver operating characteristic curve analysis revealed that the optimal cutoff point for serum CysC to indicate GDM was 0.95mg/L.

Conclusions

Serum CysC is significantly and independently associated with insulin resistance and GDM. It may be a helpful biomarker to identify the risk of GDM in Chinese pregnant women.

The determination of cystatin C in serum based on label-free and near-infrared light emitted PbS@BSA QDs

(A) The synthesis of PbS@BSA QDs. (B) The detection mechanism of cystatin C based on protease digestion to BSA and its specific inhibition effect.

Usefulness of serum cystatin C to determine the dose of vancomycin in neonate

Purpose

The vancomycin dosage regimen is regularly modified according to the patient's glomerular filtration rate (GFR). In the present study, we aimed to assess the usefulness of serum cystatin C (Cys-C) concentration, compared with serum creatinine (SCr) concentration, for predicting vancomycin clearance (CLvcm) in neonates.

Methods

We retrospectively analyzed the laboratory data of 50 term neonates who were admitted to the neonatal intensive care unit and received intravenous vancomycin, and assessed the pharmacokinetic profiles. Creatinine clearance (CLcr) and GFR based on Cys-C (GFRcys-c) were estimated using the Schwartz and Larsson formulas, respectively.

Results

The mean CLvcm (±standard deviation) was 74.52±31.17 L/hr, the volume of distribution of vancomycin was 0.67±0.14 L, and vancomycin half-life was 9.16±17.42 hours. The SCr was 0.46±0.25 mg/dL and serum Cys-C was 1.43±0.34 mg/L. The peak and trough concentrations of vancomycin were 24.65±14.84 and 8.10±5.35 mcg/mL, respectively. The calculated GFR based on serum creatinine concentration (GFR-Cr) and GFRcys-c were 70.2±9.45 and 63.6±30.18 mL/min, respectively. The correlation constant for CLvcm and the reciprocal of Cys-C (0.479, P=0.001) was significantly higher than that for CLvcm and the reciprocal of SCr (0.286, P=0.044). GFRcys-c was strongly correlated with CLvcm (P=0.001), and the correlation constant was significantly higher than that for CLvcm and CLcr (0.496, P=0.001). Linear regression analysis showed that only GFRcys-c was independently and positively correlated with CLvcm (F=41.9, P<0.001).

Conclusion

The use of serum Cys-C as a marker of CLvcm could be beneficial for more reliable predictions of serum vancomycin concentrations, particularly in neonates.

Early Acute Kidney Injury based on Serum Creatinine or Cystatin C in Intensive Care Unit after Major Trauma

BACKGROUND

Acute kidney injury (AKI) is a common problem in critically ill patients and is independently associated with increased morbidity and mortality. Recently, serum cystatin C has been shown to be superior to creatinine in early detection of renal function impairment. We compared estimated GFR based on serum cystatin C with estimated GFR based on serum creatinine for early detection of renal dysfunction according to the RIFLE criteria.

METHODS

During 9 months, three hundred post trauma patients that were referred to the intensive care unit of a referral trauma hospital were recruited. Serum creatinine and serum cystatin C were measured and the estimated GFR within 24 hours of ICU admission was calculated. The primary outcome was the incidence of AKI according to the RIFLE criteria within 2(nd) to 7(th) day of admission.

RESULTS

During the first week of ICU admission, 21% of patients experienced AKI. After adjusting for major confounders, only the patients with first day's serum cystatin level higher than 0.78 mg/l were at higher risk of first week AKI (OR=6.14, 95% CI: 2.5-14.7, P<0.001). First day's serum cystatin C and injury severity score were the major risk factors for ICU mortality (OR=3.54, 95% CI: 1.7-7.4, P=0.001) and (OR=4.6, 95% CI: 1.5-14, P=0.007), respectively.

CONCLUSION

Within 24 hours after admission in ICU due to multiple trauma, high serum cystatin C level may have prognostic value in predicting early AKI and mortality during ICU admission. However, such correlation was not seen neither with creatinine nor cystatin C based GFR.

Decreased renal function in overweight and obese prepubertal children

BACKGROUND

Obesity is a potentially modifiable risk factor for the development and progression of kidney disease, both in adults and children. We aim to study the association of obesity and renal function in children, by comparing estimated glomerular filtration rate (eGFR) in nonoverweight and overweight/obese children. Secondarily, we aim to evaluate the accuracy of equations on eGFR estimation when compared to 24-h urinary creatinine clearance (CrCl).

METHODS

Cross-sectional study of 313 children aged 8-9 y, followed in the birth cohort Generation XXI (Portugal). Creatinine and cystatin C, GFR estimated by several formulas and CrCl were compared in 163 nonoverweight and 150 overweight/obese, according to World Health Organization growth reference.

RESULTS

Overweight/obese children had significantly lower eGFR, estimated by all methods, except for CrCl and revised Schwartz formula. Despite all children having renal function in the normal range, eGFR decreased significantly with BMI z-score (differences ranging from -4.3 to -1.1 ml/min/1.73 m(2) per standard deviation of BMI). The Zappitelli combined formula presented the closest performance to CrCl, with higher correlation coefficients and higher accuracy values.

CONCLUSION

Young prepubertal children with overweight/obesity already present significantly lower GFR estimations that likely represent some degree of renal impairment associated with the complex deleterious effects of adiposity.

Is Serum Cystatin C a Predictor of Acute Pulmonary Thromboembolism in Patients With Normal Renal Function?

Early diagnosis is the key point in the management of acute pulmonary thromboembolism (PTE). There are no reports in the literature comparing the serum cystatin C levels in patients with acute PTE and normal volunteers. Therefore, in this study, we analyzed 50 patients with acute PTE and 45 healthy volunteers with normal renal function. The serum cystatin C level was significantly higher in the PTE group than in the non-PTE group (1.08 mg/dL [interquantile range (IQR) 0.79-1.56] and 0.85 mg/dL [IQR 0.77-1.03], respectively, P = .017). When determining the presence of PTE, the highest value of sensitivity and specificity was set at a cutoff value of 1.15 mg/dL with 93.3% specificity, 46.0% sensitivity, 88.5% positive predictive value, and 60.9% negative predictive value. In the multivariate model, cystatin C was significantly associated with the presence of PTE (odds ratio: 12.34, 95% CI 2.64-57.75). In conclusion, cystatin C may be an indicator of acute PTE in patients with normal renal function.

A new serum cystatin C formula for estimating glomerular filtration rate in newborns

BACKGROUND

The levels of serum cystatin C (CysC) and creatinine (Cr) were determined in small-for-gestational-age (SGA) babies and compared with those for normal term newborns appropriate for gestational age (AGA), at birth and 3 days later. We then compared a number of cysC-based, Cr-based and combined formulas for estimation of glomerular filtration rate (GFR) with the neonatal reference GFR.

METHODS

Fifty full-term SGA and 50 AGA newborns were enrolled in the study. Kidney volume measurements were performed by ultrasound for each newborn.

RESULTS

At birth, the mean level of CysC in SGA babies was 1.48 ± 0.30 mg/l in cord blood and 1.38 ± 0.18 mg/l in day 3 blood samples, and the mean Cr level, determined simultaneously, was 67.08 ± 17.62 and 55.62 ± 14.91 μmol/l, respectively. These levels did not differ significantly from those determined in AGA babies. A 10 % reduction in kidney volume was associated with an increase in CysC value of 9.3 % in cord blood. The Cr-based and Schwartz-combined equations underestimated GFR relative to CysC-based and Zappitelli-based equations at birth and 3 days later.

CONCLUSIONS

A newly constructed Cys-C based formula which includes kidney volume and body surface area in the calculations for GFR is a reliable marker of GFR compared with neonatal reference clearance values.

Reference ranges for serum β-trace protein in neonates and children younger than 1 year of age

BACKGROUND

β-Trace protein (BTP) has been proposed as an alternative endogenous marker of glomerular filtration rate. Data on BTP reference ranges in young children are scarce. We therefore aim to establish reference ranges and examine the developmental course of serum BTP in basically healthy children younger than 1 year of age.

METHODS

Single blood samples were taken from healthy children (born at gestational age ≥37 weeks) <12 months of age. Serum BTP was measured using the N latex B-trace protein assay (Siemens Diagnostics, Deerfield, IL, USA) on an Immage® 800 Rate Nephelometer (Beckman Coulter Inc. Brea, CA, USA). Serum creatinine and cystatin C were additionally determined and compared to reference values to confirm a normal renal function.

RESULTS

From June 2010 to January 2014, 95 blood samples were collected from 95 children {67.4% male; median age 120 days [inter quartile range 57-166]}. BTP was normally distributed (mean concentration 0.84±standard deviation 0.35 mg/L). Considering all children, the 50th centile BTP reference concentration was 0.82 mg/L (5th-95th centiles; 0.27-1.38). BTP concentrations were the highest in neonates and steadily declined with increasing age (Spearman's rank correlation was -0.415, p=0.002). No gender differences were found.

CONCLUSIONS

Our data provide a BTP reference range for the first year of life. Seeing the biological pattern of BTP, with only a limited postnatal decline, this marker might offer a promising alternative to serum creatinine-based methods for estimating glomerular filtration rate in newborns.

Use of cystatin C and serum creatinine for the diagnosis of contrast-induced nephropathy in patients undergoing contrast-enhanced computed tomography at an oncology centre

OBJECTIVE

Our aim was to assess renal function using as laboratory measurements serum creatinine and cystatin C concentrations before and after administration of low-osmolarity (nonionic) iodinated contrast medium in patients with cancer undergoing computed tomography (CT).

METHODS

This prospective study included 400 oncologic outpatients. Serum creatinine and cystatin C concentrations were measured before and 72 h after contrast administration. Glomerular filtration rates (GFRs) were estimated using serum creatinine-based [Modification of Diet in Renal Disease (MDRD) and Cockroft-Gault and cystatin C based (Larsson) equations. Exploratory data analysis was performed. The nonparametric Wilcoxon test was used to compare pre and post contrast of test results and estimated clearance. The confidence interval used in the analysis was 95%.

RESULTS

Compared with the pre-contrast values, the mean serum creatinine concentration was significantly higher and average GFRs estimated using MDRD and Cockcroft-Gault equations were significantly lower after the administration of contrast (p <0.001). It was also observed a significant increase after contrast in the concentration of Cystatin C (p = 0.015). In addition, a decrease in GFR estimated using the average Larsson (p = 0.021) was observed between time points. However, none of the patients presented clinically significant nephropathy.

CONCLUSIONS

Assessment using serum creatinine and cystatin C concentrations showed changes in renal function among patients with cancer undergoing contrast-enhanced CT examination in this study. No significant renal damage related to the use of low-osmolarity iodinated contrast medium of the type and dosage employed in this study was observed. This contrast medium is thus safe for use in patients with cancer.

Novel biomarkers of acute kidney injury: Evaluation and evidence in urologic surgery

Patients undergoing urologic surgery are at risk of acute kidney injury (AKI) and consequently long-term deterioration in renal function. AKI is further associated with significantly higher odds of perioperative complications, prolonged hospital stay, higher mortality and costs. Therefore, better awareness and detection of AKI, as well as identification of AKI determinants in the urological surgery setting is warranted to pre-empt and mitigate further deterioration of renal function in patients at special risk. New consensus criteria provide precise definitions of diagnosis and description of the severity of AKI. However, they rely on serum creatinine (SCr), which is known to be an inaccurate marker of early changes in renal function. Therefore, several new urinary and serum biomarkers promise to address the gap associated with the use of SCr. Novel biomarkers may complement SCr measurement or most likely improve the diagnostic accuracy of AKI when used in combinations. However, novel biomarkers have to prove their clinical applicability, accuracy, and cost effectiveness prior to implementation into clinical practice. Most preferably, novel biomarkers should help to positively improve a patient’s long-term renal functional outcomes. The purpose of this review is to discuss currently available biomarkers and to review their clinical evidence within urologic surgery settings.

Biological validation of feline serum cystatin C: The effect of breed, age and sex and establishment of a reference interval

Chronic kidney disease (CKD) is common in cats, but the routine renal markers, serum creatinine (sCr) and urea, are not sensitive or specific enough to detect early CKD. Serum cystatin C (sCysC) has advantages over sCr, both in humans and dogs, and sCysC concentration is significantly higher in cats with CKD than in healthy cats. The objective of this study was to determine the effect of age, sex and breed on feline sCysC and to establish a reference interval for feline sCysC. In total, 130 healthy cats aged 1-16 years were included. sCysC was determined using a validated particle-enhanced nephelometric immunoassay. sCr, urea, urine specific gravity, urinary protein:creatinine ratio (UPC) and systolic blood pressure (SBP) were also measured. No significant differences in sCysC concentration were observed among young, middle-aged and geriatric cats, female intact, female neutered cats, male intact and male neutered cats, or among purebred and domestic short-or longhaired cats. The 95% reference interval for feline sCysC was determined to be 0.58-1.95 mg/L. sCr was significantly higher in geriatric cats than young cats. Serum urea in geriatric cats was significantly higher than in middle-aged and young cats (P = 0.004 and P <0.001, respectively). SBP in geriatric cats was significantly higher than in both middle-aged and young cats (P = 0.004 and P = 0.040, respectively). Male neutered and female neutered cats had significantly higher serum urea concentrations than female intact cats (P = 0.003 and P = 0.006, respectively). Male intact cats had a significantly higher UPC than female intact and female neutered cats (P = 0.02 for each comparison). There were no significant differences among sex groups for USG. It is of concern that sCysC in the majority of cats with CKD in previous studies falls within the reference interval calculated in this study. Further studies are warranted to evaluate the diagnostic value of sCysC as a renal marker in cats.

Cystatin C is a disease-associated protein subject to multiple regulation

A protease inhibitor, cystatin C (Cst C), is a secreted cysteine protease inhibitor abundantly expressed in body fluids. Clinically, it is mostly used to measure glomerular filtration rate as a marker for kidney function due to its relatively small molecular weight and easy detection. However, recent findings suggest that Cst C is regulated at both transcriptional and post‐translational levels, and Cst C production from haematopoietic cell lineages contributes significantly to the systematic pools of Cst C. Furthermore, Cst C is directly linked to many pathologic processes through various mechanisms. Thus fluctuation of Cst C levels might have serious clinical implications rather than a mere reflection of kidney functions. Here, we summarize the pathophysiological roles of Cst C dependent and independent on its inhibition of proteases, outline its change of expression by various stimuli, and elucidate the regulatory mechanisms to control this disease‐related protease inhibitor. Finally, we discuss the clinical implications of these findings for translational gains.

Cystatin C and Its Role in Patients with Type 1 and Type 2 Diabetes Mellitus

Diabetes mellitus is the commonest cause of CKD. It is the leading cause of new patients requiring renal replacement therapy, accounting for 40%, 34%, and 30% of cases in United States, Germany, and Australia, respectively. Recent studies have shown that a low-molecular weight protein, cystatin C, freely filtered by the kidneys is a novel biomarker that may be used for detection of early renal dysfunction in patients with type 1 or type 2 diabetes. Cystatin C has also been shown to detect cardiovascular disease in patients with diabetes and it may also be linked with incident type 2 diabetes in obese patients. We aim to review current evidence based literature on use of cystatin C for early detection of diabetic nephropathy due to type 1 and type 2 diabetes in comparison to conventional methods and explore its association with other comorbidities.

Chronic kidney disease screening methods and its implication for Malaysia: an in depth review

Chronic Kidney Disease has become a public health problem, imposing heath, social and human cost on societies worldwide. Chronic Kidney Disease remains asymptomatic till late stage when intervention cannot stop the progression of the disease. Therefore, there is an urgent need to detect the disease early. Despite the high prevalence of Chronic Kidney Disease in Malaysia, screening is still lacking behind. This review discusses the strengths and limitations of current screening methods for Chronic Kidney Disease from a Malaysian point of view. Diabetic Kidney Disease was chosen as focal point as Diabetes is the leading cause of Chronic Kidney Disease in Malaysia. Screening for Chronic Kidney Disease in Malaysia includes a urine test for albuminuria and a blood test for serum creatinine. Recent literature indicates that albuminuria is not always present in Diabetic Kidney Disease patients and serum creatinine is only raised after substantial kidney damage has occurred.  Recently, cystatin C was proposed as a potential marker for kidney disease but this has not been studied thoroughly in Malaysia.  Glomerular Filtration Rate is the best method for measuring kidney function and is widely estimated using the Modification of Diet for Renal Disease equation. Another equation, the Chronic Kidney Disease Epidemiology Collaboration Creatinine equation was introduced in 2009. The new equation retained the precision and accuracy of the Modification of Diet for Renal Disease equation at GFR < 60ml/min/1.73m2, showed less bias and improved precision at GFR>60ml/min/1.73m2. In Asian countries, adding an ethnic coefficient to the equation enhanced its performance. In Malaysia, a multi-ethnic Asian population, the Chronic Kidney Disease Epidemiology Collaboration equation should be validated and the Glomerular Filtration Rate should be reported whenever serum creatinine is ordered. Reporting estimated Glomerular Filtration Rate will help diagnose patients who would have been otherwise missed if only albuminuria and serum creatinine are measured.

Comparative performances of the new chronic kidney disease epidemiology equations incorporating cystatin C for use in cancer patients

AIM

In cancer patients receiving chemotherapy treatment, accurate assessment of kidney function is required. The aim of our study was to investigate whether the inclusion of cystatin C together with creatinine in prediction equations would improve the prediction of glomerular filtration rate (GFR).

METHODS

Plasma creatinine and cystatin C were analyzed in 155 patients (cancer, n = 80, kidney donors, n = 75) undergoing (99m) Technetium diethylenepentaacetic (Tc-DTPA) GFR clearance. Equations by the CKD-EPI (chronic kidney disease epidemiology) group (creatinine-, creatinine + cystatin C-, cystatin C-based, respectively) and Cockcroft-Gault were compared with Tc-DTPA GFR by difference plots, receiver operator characteristics curve analysis, root mean square error, chi-squared analysis and percentage concordance according to carboplatin dosage. Comparisons between two creatinine methodologies (enzymatic vs Jaffe) were also performed.

RESULTS

In the overall group, the combination creatinine and cystatin C equation had 69% of results within 20% of GFR (P20), a sensitivity of 86.3% and a specificity of 73.1% to detect reduced GFR at <90 mL/min/1.73 m(2), and a concordance of 78%. In contrast, the traditional Cockcroft-Gault equation had a P20 of 38.0%, with a large underestimation to predict GFR, thereby accounting for approximately 45% of dosing discordance. No obvious differences were obtained when comparing the performance of equations using the two creatinine methodologies.

CONCLUSION

The inclusion of cystatin C in the CKD-EPI equations improved the prediction of kidney function in the overall population, although probably not sufficiently for it to be favored over radioisotopic GFR for guiding chemotherapy. More research is warranted to further improve estimated GFR equations for these purposes.

A meta-analysis on diagnostic value of serum cystatin C and creatinine for the evaluation of glomerular filtration function in renal transplant patients

OBJECTIVES

This meta-analysis aimed to perform a systematic review on comparing the diagnostic value of serum cystatin C and creatinine for glomerular filtration rate in renal transplant patients.

METHODS

The data was extracted into 2×2 table after the articles were assessed by the tool of QUADAS and heterogeneity analysis. The SROC curve and meta-analysis were performed by MetaDisc1.4.

RESULTS

Meta-analysis showed that the serum cystatin C had no heterogeneity (P=0.418, I2=2.2%, DOR=25.03), while creatinine heterogeneity was high (P=0.109, I2=37.5%, DOR=9.11). The values of SEN, SPE and SAUC were calculated as 0.86, 0.70 and 0.9015 for cystatin C, and 0.78, 0.73 and 0.8285 for creatinine individually. This study utilized GFR detection and subgroups analysis by cutoff. The PLR was 6.13 and the NLR was 0.12 for cystatin C, compared to SCr (3.72, 0.32). There was homogeneity among these studies using PENIA testing for cystatin C (χ2=2.61, P=0.4560, I2=0.0%.

CONCLUSIONS

There were significant correlations among cystatin C , creatinine and glomerular filtration rate (GFR). Cystatin C had more sensitivity but less specificity than creatinine for evaluation of GFR. Cystatin C had strong ability in diagnosing renal function after renal transplant and ruling out diagnostic efficacy.

Cardiorenal syndrome type 2: from diagnosis to optimal management

The deterioration of renal function, which is linked to chronic heart failure by a chronological and causal relationship (ie, the so-called cardiorenal syndrome [CRS] type 2), has recently become a matter of growing debate. This debate has concerned the efficacy, safety, and cost effectiveness of the therapies that have been implemented thus far for this syndrome (for example, the intravenous [IV] loop diuretics, such as repeated IV boluses or slow IV infusions, as well as mechanical fluid removal, particularly by means of isolated ultrafiltration [IUF]). Further controversies have also emerged concerning the optimal dosage and timing of some evidence-based drugs, such as angiotensin-converting-enzyme inhibitors. The present review summarizes the currently used diagnostic tools for detecting renal damage in CRS type 2. Subsequently, the meaning of worsening renal function is outlined, as well as the sometimes inconsistent therapeutic schemes that have been implemented in order to prevent or counteract worsening renal function. The need to elaborate upon more detailed and comprehensive scientific recommendations for targeted prevention and/or therapy of CRS type 2 is also underlined. The measures usually adopted (such as the more accurate modulation of loop diuretic dose, combined with the exploitation of other diuretics that are able to achieve a sequential blockade of the nephron, as well as the use of IV administration for loop diuretics) are briefly presented. The concept of diuretic resistance is illustrated, along with the paramount operational principles of IUF in diuretic-resistant patients. Some controversies regarding the comparison of IUF with stepped diuretic therapy in patients with CRS type 2 are also addressed.

Renal function assessment in child and adolescent heart transplant recipients during routine cardiac catheterization

CKD identification after pediatric heart transplantation (PHT) is limited by inaccuracies in estimates of GFR. We hypothesized that GFR can be measured by a modified iohexol clearance protocol in PHT recipients and that the CKiD formula provides a better estimate of GFR than other estimating equations. A cross-sectional study of PHT recipients, ages 2-18 yr, undergoing coronary angiography was undertaken. The angiography dose of iohexol was divided by the area under the curve from three iohexol levels post-infusion to calculate GFR. Agreement between iGFR and multiple estimating equations (eGFR) was assessed. In 31 subjects, median age was 15.0 yr (IQR 7.6, 16.6). Mean iGFR was 93.8 (s.d. 22.5) mL/min/1.73 m(2) ; 16 (52%) had an iGFR <90 mL/min/1.73 m(2) . The full CKiD formula (mean eGFR 88.9, s.d. 14.9) had low bias (-5.0), narrowest 95% limits of agreement (-42.0, 32.1), highest 30% (94%) and 10% (52%) accuracy, and highest correlation coefficient (0.576) relative to iGFR. We describe a novel modified iohexol clearance method to assess GFR after PHT. Over half of the cohort had an iGFR <90, suggesting CKD. The full CKiD formula performs best with respect to bias, accuracy, and correlation.

Heart failure mortality according to acute variations in N-terminal pro B-type natriuretic peptide and cystatin C levels

AIM

Changes in N-terminal pro B-type natriuretic peptide (NT-proBNP) levels and cystatin C (CysC) are predictors of adverse outcomes in acute heart failure. This study assess whether NT-proBNP variations might provide independent information in addition to that obtained from CysC levels.

METHODS

NT-proBNP levels were assessed in patients admitted due to acute heart failure using an observational study. Patients were classified as follows: group 1, those with a decrease in NT-proBNP levels of at least 30% from admission to 4 weeks after discharge; group 2, those with no significant changes in levels; and group 3, those who showed an increase in NT-proBNP of 30%. A multivariable Cox regression model and c-statistics were used. The primary end-point was all-cause mortality at 1-year follow-up.

RESULTS

A total of 195 patients completed the follow-up. The mortality rate reached 20.5% (40 patients); 14 out of the 32 in group 3. The cumulative incidence of death, according to the change in NT-proBNP and Kaplan-Meier analysis, showed a significant increase in group 3 (log-rank P = 0.004). In the multivariable analysis, NT-proBNP variation for group 3 (hazard ratio 4.27; P <0.001) and for group 2 (hazard ratio 2.19; P = 0.043) in comparison with group 1 were independently associated with all-cause mortality, as well as anemia, hyponatremia, and admission CysC levels. Patients in group 3, and those with levels of serum CysC above the median, were also associated with slight increase in mortality.

CONCLUSION

An increase of at least 30% in NT-proBNP levels after hospitalization is related to all-cause mortality in patients with acute heart failure and provides supplementary prognostic information in patients with high levels of CysC. A decrease in NT-proBNP of at least 30% is a desirable target to achieve.

Albuminuria correlates with hemolysis and NAG and KIM-1 in patients with sickle cell anemia

BACKGROUND

Although hyperfiltration and albuminuria are common pathological conditions, kidney injury (KI) biomarkers have been seldom studied in individuals with sickle cell anemia (SCA).

METHODS

We undertook a cross-sectional assessment of urine KI biomarkers in children and adults with SCA with and without albuminuria and a normal estimated glomerular filtration rate (eGFR). Albumin, KI molecule 1 (KIM-1), N-acetyl-ß-D-glucosaminidase (NAG), endothelin-1 and transforming growth factor-β1 (TGF-β1) were measured. Assays were normalized by urine creatinine. Urine intracellular hemosiderin and serum lactate dehydrogenase (LDH) were assessed as markers of hemolysis. Albuminuria was associated to the biomarkers by Pearson and Spearman correlation coefficients. Differences between the albuminuria (yes, no) groups were assessed by the t test.

RESULTS

Nineteen patients with albuminuria (mean urine albumin/creatinine 527.14 ± 1070 mg/g, range 38.3--190 mg/g) and 19 patients without albuminuria (mean urine albumin/creatinine 15.93 ± 5.17 mg/g, range 7.9-28.4 mg/g) were studied. The age range for the whole group was 11-48 years, and 47 % were males. Patients with albuminuria were older, had lower hematocrit, were more likely to test positive for urine hemosiderin and had a higher KIM-1 (P = 0.0035) and NAG/ creatinine ratios (P = 0.0062). Urine hemosiderin strongly correlated to a higher LDH level (P < 0.001).

CONCLUSIONS

Despite a normal or increased eGFR, KI biomarkers were detected in the urine of individuals with SCA. NAG, KIM-1 and urine hemosiderin correlated with the presence of albuminuria.

Comparison of estimated glomerular filtration rate by the chronic kidney disease epidemiology collaboration (CKD-EPI) equations with and without Cystatin C for predicting clinical outcomes in elderly women

BACKGROUND

Reduced estimated glomerular filtration rate (eGFR) using the cystatin-C derived equations might be a better predictor of cardiovascular disease (CVD) mortality compared with the creatinine-derived equations, but this association remains unclear in elderly individuals.

AIM

The aims of this study were to compare the predictive values of the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI)-creatinine, CKD-EPI-cystatin C and CKD-EPI-creatinine-cystatin C eGFR equations for all-cause mortality and CVD events (hospitalizations±mortality).

METHODS

Prospective cohort study of 1165 elderly women aged>70 years. Associations between eGFR and outcomes were examined using Cox regression analysis. Test accuracy of eGFR equations for predicting outcomes was examined using Receiver Operating Characteristic (ROC) analysis and net reclassification improvement (NRI).

RESULTS

Risk of all-cause mortality for every incremental reduction in eGFR determined using CKD-EPI-creatinine, CKD-EPI-cystatin C and the CKD-EPI-creatinine-cystatic C equations was similar. Areas under the ROC curves of CKD-EPI-creatinine, CKD-EPI-cystatin C and CKD-EPI-creatinine-cystatin C equations for all-cause mortality were 0.604 (95%CI 0.561-0.647), 0.606 (95%CI 0.563-0.649; p = 0.963) and 0.606 (95%CI 0.563-0.649; p = 0.894) respectively. For all-cause mortality, there was no improvement in the reclassification of eGFR categories using the CKD-EPI-cystatin C (NRI -4.1%; p = 0.401) and CKD-EPI-creatinine-cystatin C (NRI -1.2%; p = 0.748) compared with CKD-EPI-creatinine equation. Similar findings were observed for CVD events.

CONCLUSION

eGFR derived from CKD-EPI cystatin C and CKD-EPI creatinine-cystatin C equations did not improve the accuracy or predictive ability for clinical events compared to CKD-EPI-creatinine equation in this cohort of elderly women.

Serum creatinine role in predicting outcome after cardiac surgery beyond acute kidney injury

Serum creatinine is still the most important determinant in the assessment of perioperative renal function and in the prediction of adverse outcome in cardiac surgery. Many biomarkers have been studied to date; still, there is no surrogate for serum creatinine measurement in clinical practice because it is feasible and inexpensive. High levels of serum creatinine and its equivalents have been the most important preoperative risk factor for postoperative renal injury. Moreover, creatinine is the mainstay in predicting risk models and risk factor reduction has enhanced its importance in outcome prediction. The future perspective is the development of new definitions and novel tools for the early diagnosis of acute kidney injury largely based on serum creatinine and a panel of novel biomarkers.

Application of creatinine- and/or cystatin C-based glomerular filtration rate estimation equations in elderly Chinese

Background

No conventional creatinine- or cystatin C-based glomerular filtration rate (GFR) estimation equation performed consistently outstandingly in elderly Chinese in our previous studies. This research aimed to further evaluate the performance of some recently proposed estimation equations based on creatinine and cystatin C, alone or combined, in this specific population.

Materials and methods

The equations were validated in a population totaling 419 participants (median age 68 [range 60–94] years). The estimated GFR (eGFR) calculated separately by ten equations was compared with the reference GFR (rGFR) measured by the ^99mTc-DTPA renal dynamic imaging method.

Results

Median serum creatinine, cystatin C, and rGFR levels were 0.93 mg/L, 1.13 mg/L, and 74.20 mL/min/1.73 m², respectively. The Chinese population-developed creatinine- and cystatin C-based (Cscr-cys) equation yielded the least median absolute difference (8.81 vs range 9.53–16.32, P<0.05, vs the Chronic Kidney Disease Epidemiology Collaboration serum creatinine equation), the highest proportion of eGFR within 15% and 30% of rGFR (P₁₅ and P₃₀, 55.13 and 85.44, P<0.05 and P<0.01, vs the Chronic Kidney Disease Epidemiology Collaboration serum creatinine equation), and the lowest root mean square error (14.87 vs range 15.30–22.45) in the whole cohort. A substantial agreement of diagnostic consistency between eGFR and rGFR (with a kappa 0.61–0.80) was also observed with the Cscr-cys equation. Moreover, measures of performance in the Cscr-cys equation were consistent across normal to mildly injured GFR strata and individuals aged ≤80 years. Among all the Cscr-cys equations, the elderly Chinese-developed creatinine-based (CEscr) equation performed best in this specific population. Nevertheless, none of the equations achieved ideal manifestation in the moderately to severely GFR-injured group or in individuals aged ≥80 years.

Conclusion

The Cscr-cys equation appeared to be optimal in elderly Chinese among the investigated equations. If cystatin C is not available, the CEscr equation is an acceptable alternative. A multicenter study with abundant subjects to develop an apposite formula for elderly Chinese is assumed to be essential.

Comparison of estimated GFR equations based on serum cystatin C alone and in combination with serum creatinine in patients with coronary artery disease

OBJECTIVE

Several new equations (GFRCKD-EPI-cr, GFRCKD-EPI-CysC, GFRCKD-EPI Cr+CysC) are used for the calculation of estimated GFR (eGFR) to evaluate renal function. These equations explicitly demonstrate the association of coronary artery disease (CAD) and severe renal impairment cases. However, these equations are considered insufficient to explain the relation with normal or mildly impaired eGFR and CAD. Our hypothesis was to indicate the inversely proportional relationship of eGFR values, calculated by the different equations, with the presence of CAD in patients with normal or mildly impaired renal function.

METHODS

Eighty-eight patients who underwent elective coronary angiographic intervention were enrolled into the study. The study population was divided into two groups based on angiographic documents: patients with normal coronary arteries (CAD-) and patients with CAD (CAD +). These patients were stable and decided to implement angiography for the purpose of suspicion about CAD and control. Since it is thought that eGFR equations based on creatinine are inadequate to determine chronic kidney disease (CKD) and overestimate CKD diagnosis, cystatin C-based equations are considered an alternative. Due to the potential effects of inflammatory events of the markers used in equations, patients with diabetes mellitus, severe CKD, and inflammatory bowel disease were excluded from the study.

RESULTS

The average age of all participants was 51.93±9.31 (32-65 years); 80.7% (n=71) was male. A statistical difference was found between the CAD (-) group and the CAD (+) group in terms of the variables of age (45.46±8.48 vs. 54.95±8.11, p<0.001), gender (67.9% vs. 86.7%, male, p=0.037), cystatin C values (1.37±0.34 vs. 0.85±0.39, p<0.001), and GFR equations defined by the Chronic Kidney Disease Epidemiology: GFRCKD-EPI-cr (85.86±14.20 vs. 79.45±10.25, p=0.018), GFRCKD-EPI-CysC (58.61±21.87 vs. 100.82±32.00, p<0.001), and GFRCKD-EPI Cr+CysC (68.29±13.49 vs. 90.75±18.34, p<0.001). After adjustment of the variables in multiple regression analyses, only age (OR, 1.199; 95% CI, 1.077 to 1.335, p=0.001), gender (OR, 8.252; 95% CI, 0.223 to 55.659, p=0.030), and the GFRCKD-EPI-CysC equation (OR, 1.059; 95% CI, 1.028 to 1.090, p<0.001) were detected as predictors for presence of CAD.

CONCLUSION

GFR equations based on cystatin C or combined with creatinine may have superiority to GFR equations based on creatinine alone in CAD patients. However, the impact of different variables on the GFRCKD-EPI-CysC equation should not be ignored in specific groups, such as CAD.

Elevated urinary levels of cystatin C and neutrophil gelatinase-associated lipocalin in Henoch-Schönlein purpura patients with renal involvement

Henoch-Schönlein purpura (HSP) is a commonest systemic vasculitis in childhood. The long-term prognosis of HSP is determined by the degree of renal involvement. The aim of this study is to search novel clinically applicable biomarkers to evaluate renal involvement in HSP patients. 20 bio-indexes in urine samples were simultaneously screened by antibody array assay. We indicated that urinary levels of cystatin C (Cys C) and neutrophil gelatinase-associated lipocalin (NGAL) in HSP patients with renal involvement were significantly higher than those without renal involvement and healthy controls. Furthermore, ELISA was used to analyze urinary Cys C and NGAL levels in HSP patients with or without renal involvement, atopic dermatitis (AD) patients and healthy controls. Our results demonstrated that urinary Cys C and NGAL levels in HSP patients with renal involvement were significantly elevated, when compared with those without renal involvement, AD patients and control subjects. In addition, by receiver operating characteristic (ROC) curve analysis, we demonstrated that the area under the ROC curve of NGAL (0.789) was larger than that of Cys C (0.692). Taken together, we show firstly that urinary Cys C and NGAL levels is abnormally elevated in HSP patients with renal involvement. We suggest that urinary Cys C and NGAL are novel useful biomarkers of renal involvement in HSP patients.

Cystatin C, a novel indicator of renal function, reflects severity of cerebral microbleeds

BACKGROUND

Chronic renal insufficiency, diagnosed using creatinine based estimated glomerular filtration rate (GFR) or microalbumiuria, has been associated with the presence of cerebral microbleeds (CMBs). Cystatin C has been shown to be a more sensitive renal indicator than conventional renal markers. Under the assumption that similar pathologic mechanisms of the small vessel exist in the brain and kidney, we hypothesized that the levels of cystatin C may delineate the relationship between CMBs and renal insufficiency by detecting subclinical kidney dysfunction, which may be underestimated by other indicators, and thus reflect the severity of CMBs more accurately.

METHODS

Data was prospectively collected for 683 patients with ischemic stroke. The severity of CMBs was categorized by the number of lesions. Patients were divided into quartiles of cystatin C, estimated GFR and microalbumin/creatinine ratios. Ordinal logistic regression analysis was used to examine the association of each renal indicator with CMBs.

RESULTS

In models including both quartiles of cystatin C and estimated GFR, only cystatin C quartiles were significant (the highest vs. the lowest, adjusted OR, 1.88; 95% CI 1.05-3.38; p = 0.03) in contrast to estimated GFR (the highest vs. the lowest, adjusted OR, 1.28; 95% CI 0.38-4.36; p = 0.70). A model including both quartiles of cystatin C and microalbumin/creatinine ratio also showed that only cystatin C quartiles was associated with CMBs (the highest vs. the lowest, adjusted OR, 2.06; 95% CI 1.07-3.94; p = 0.03). These associations were also observed in the logistic models using log transformed-cystatin C, albumin/creatinine ratio and estimated GFR as continuous variables. Cystatin C was a significant indicator of deep or infratenorial CMBs, but not strictly lobar CMBs. In addition, cystatin C showed the greatest significance in c-statistics for the presence of CMBs (AUC = 0.73 ± 0.03; 95% CI 0.66-0.76; p = 0.02).

CONCLUSION

Cystatin C may be the most sensitive indicator of CMB severity among the renal disease markers.

Analytical validation of a human particle-enhanced nephelometric assay for cystatin C measurement in feline serum and urine

BACKGROUND

In people and dogs, Cystatin C (CysC), a renal glomerular and tubular marker, seems superior to serum creatinine to estimate the glomerular filtration rate (GFR). A particle-enhanced nephelometric immunoassay is available to measure human CysC, but there are no reports in cats.

OBJECTIVE

The goal of this study was the validation of the human CysC nephelometric assay with feline serum and urine, and to perform a pilot study comparing serum and urine CysC between healthy cats and cats with chronic kidney disease (CKD).

METHODS

Western blot analysis was used to assess cross-reactivity between the polyclonal rabbit anti-human CysC antibody and feline CysC. Imprecision and linearity were determined for feline serum and urine CysC. Serum and urine CysC were measured in 10 healthy and 10 CKD cats.

RESULTS

Cross-reactivity between the polyclonal rabbit anti-human CysC antibody and feline CysC was demonstrated. Intra- and inter-assay coefficients of variation in feline serum and urine were 1.3% and 0.4%, and 12.5%, and 4.1%, respectively. Cats with CKD had a significantly higher serum CysC concentration (1.24 [0.63-2.99] vs 0.79 [0.43-1.05] mg/L; P = .02) and urine CysC/urinary Creatinine (uCr) ratio (565.6 [0-1311] vs < 0.049/uCr mg/mol; P = .005) compared with healthy cats.

CONCLUSIONS

The human nephelometric assay showed satisfactory validation results for feline CysC. Cats with CKD had a significantly higher sCysC concentration and uCysC/uCr ratio compared with healthy cats. Additional studies are necessary to evaluate CysC as an early marker of renal damage in cats.

Assessment of cystatin C and cystatin C-based GFR formulas in reflux nephropathy

OBJECTIVE

Early identification of reflux nephropathy (RN) could reduce the frequency of chronic kidney disease (CKD) caused by vesicoureteral reflux (VUR). We aimed to assess whether cystatin C has value for determining RN in children with VUR.

MATERIALS AND METHODS

Ninety-three children with VUR were classified into two groups according to the presence of renal parenchymal scarring (RS). Patients with RS were divided into three subgroups according to scar grade. Serum cystatin C, serum creatinine (Scr) and urine creatinine were measured. eGFR values of the patients were calculated with Scr-based, cystatin C-based and combined formulas.

RESULTS

Cystatin C was significantly higher in patients with RS than patients without RS and declined in parallel with grade of RS (p = 0.01). Scr was not significant in patients with and without RS. It was only significant between mild and severe scar subgroups (p < 0.05). All eGFR values were lower in RS (+) patients compared with RS (-) patients. All eGFR equations were negatively correlated with grade of RS (p < 0.05).

CONCLUSION

Cystatin C could be a useful marker for identifying the risk and severity of RN in patients with VUR. Renal functions could be more accurately determined with Scr-cystatin C combined eGFR equations.