Serum cystatin C as a new marker for noninvasive estimation of glomerular filtration rate and as a marker for early renal impairment

Reduced renal function in patients with Myotonic Dystrophy type 1 and the association to CTG expansion and other potential risk factors for chronic kidney disease

Myotonic dystrophy type 1 (DM1) affects several organs. Disease severity and age at onset are correlated to the CTG repeat expansion. The aim of this study was to assess renal function and the association to numbers of CTG repeat expansion in patients with DM1. Ninety-eight patients with DM1 were included. Glomerular filtration rate (measured GFR) was measured using iohexol clearance. Data on CTG repeats were available in 83/98 (85%) patients. The overall mGFR was 74 (16) ml/min/1.73 m² (range 38-134). Sixty-four patients (69%) had a mild and sixteen patients (17%) a moderate decrease in renal function (mGFR 60-89 and 30-59 ml/min/1.73 m², respectively). No correlations were found between CTG repeats and mGFR (r = 0.10, p = 0.4) or between CTG repeats and serum cystatin C (r = 0.12, p = 0.29). CTG repeats was positively correlated to creatinine-based estimates of GFR (eGFR) (modified diet in renal disease r = 0.49, p < 0.001, CKD-EPI creatinine equation; r = 0.50, p < 0.001), but analyses using Structural Equation Modeling showed no correlation. The correlation was explained by an indirect effect via serum creatinine and skeletal muscle mass index. In conclusion, patients with DM1 seem to have a slight decrease in renal function but there is no association between renal function and the number of CTG repeats, a marker of disease severity.

The Relationship between Renal Function and Bone Marrow Density in Healthy Korean Women

OBJECTIVES

The relationship between renal function and bone mineral density (BMD) is controversial. We evaluated the relationship between markers of renal function and BMD in healthy Korean women.

METHODS

A total of 1,093 women who visited the health promotion center at Pusan National University hospital were included in the cross-sectional study. We divided the study population into two groups by BMD: osteopenia-osteoporosis and normal in the lumbar and femur regions, respectively. We compared the relationship between renal function and BMD using a logistic regression model and used SAS 9.3 (SAS Institute, Inc., Cary, NC, USA) for all statistical analysis.

RESULTS

Blood urea nitrogen (BUN), creatinine, and cystatin C (Cys-C) were correlated with BMD in both the normal and osteopenia-osteoporosis groups, and in logistic regression analysis, BUN and Cys-C were correlated with lumbar and femur BMD. However, after we adjusted for age, menopause, and body mass index, only creatinine showed a negative correlation with lumbar BMD, and estimated glomerular filtration rate (eGFR) was related positively with femur BMD.

CONCLUSIONS

Serum creatinine could be a marker for lumbar BMD and eGFR for femur BMD in Korean women without overt nephropathy.

Nicardipine Effects on Renal Function During Spine Surgery

STUDY DESIGN

Single-center, prospective, randomized, and single-blinded clinical trial was conducted in patients (n=64) undergoing anterior or posterior spinal interbody fusion.

OBJECTIVE

To investigate the renal protective effect of nicardipine during deliberate hypotension for spine surgery by measuring creatinine clearance (Ccr), serum cystatin C, urine output, and fractional excretion of sodium (FENa).

SUMMARY OF BACKGROUND DATA

Deliberate hypotension during spine surgery may result in ischemic tissue damage of the kidney. Nicardipine is reported to dilate the renal artery and increase glomerular filtration rate. Previous studies reported the renal protective effect of nicardipine during cardiac surgery under cardiopulmonary bypass and robot-assisted laparoscopic surgery.

MATERIALS AND METHODS

Patients were randomized to receive nicardipine (nicardipine group, n=32) or normal saline (control group, n=32). Deliberate hypotension of mean arterial pressure at 50-65 mm Hg was maintained during surgery. Ccr, serum cystatin C, urine output, and FENa were measured before surgery, after surgery, and postoperative day 1 (POD1). The RIFLE (risk, injury, failure, loss, and end stage renal disease) criteria of the patients were evaluated.

RESULTS

In the nicardipine group, Ccr at POD1 was increased compared with that after surgery. In both groups, serum cystatin C at POD1 was decreased compared with that before surgery and urine output at POD1 was decreased compared with that after surgery. FENa at POD1 in the control group was higher than that in the nicardipine group and was increased compared with that after surgery. Using RIFLE criteria, 6 patients in the control group and 2 patients in the nicardipine group were classified as having acute kidney injury.

CONCLUSIONS

Nicardipine increased Ccr and attenuated the increase in FENa at POD1 in patients undergoing spine surgery under deliberate hypotension.

Two-dimensional ytterbium oxide nanodisks based biosensor for selective detection of urea

Herein, we demonstrate synthesis and application of two-dimensional (2D) rectangular ytterbium oxide (Yb₂O₃) nanodisks via a facile hydrothermal method. The structural, morphological, compositional, crystallinity, and phase properties of as-synthesized nanodisks were carried out using several analytical techniques that showed well defined 2D rectangular nanodisks/sheet like morphologies. The average thickness and edge length of the nanosheet structures were 20 ± 5nm and 600 ± 50nm, respectively. To develop urea biosensor, glassy carbon electrodes (GCE) were modified with Yb₂O₃ nanodisks, followed by urease immobilization and Nafion membrane covering (GCE/Yb₂O₃/Urease/Nafion). The fabricated biosensor showed sensitivity of 124.84μAmM^-1cm^-2, wide linear range of 0.05-19mM, detection limit down to ~ 2μM, and fast response time of ~ 3s. The developed biosensor was also used for the urea detection in water samples through spike-recovery experiments, which illustrates satisfactory recoveries. In addition, the obtained desirable selectivity towards specific interfering species, long-term stability, reproducibility, and repeatability further confirm the potency of as-fabricated urea biosensor.

Early markers of kidney dysfunction and cognitive impairment among older adults

BACKGROUND

Age-related decline in kidney function can be an important risk factor for cognitive impairment in older adults. In this study, we examined several kidney function measures for the association with cognitive function in older adults in hope to identify early and sensitive markers that can be used for the detection or screening for cognitive impairment.

METHODS

A total of 1982 older participants (aged ≥60years) in the 1999-2002 National Health and Nutrition Examination Survey was analyzed for the association between kidney function and cognitive impairment using multivariate logistic regression and general linear models. Cognitive functioning was assessed during the household interview using a version of the Digit Symbol Substitution Test of the Wechsler Adult Intelligence Scale III. In our study, participants with a score of <31, the 25th percentiles of the distribution, or who were unable to complete the sample exercise due to cognitive limitations were classified as having cognitive impairment.

RESULTS

Of 1982 older adults, 503 were having cognitive impairment (weighted prevalence, 15.38%). Among the kidney function measures that we examined, the levels of serum cystatin C and urinary albumin were found being significantly associated with cognitive impairment after adjusting for age, sex, race/ethnicity, poverty status, education, physical activity, BMI, cigarette smoking, and alcohol consumption. Cognitive functioning scores were significantly decreasing with increasing levels of kidney dysfunction markers.

CONCLUSION

Serum cystatin C and urinary albumin that are early markers of chronic kidney disease might serve as early and effective markers for cognitive decline in older adults. Mechanisms underlying the observed association need to be further characterized.

Elevated Plasma Homocysteine Level Increased the Risk of Early Renal Impairment in Acute Ischemic Stroke Patients

Renal insufficiency is associated with the prognosis of acute ischemic stroke (AIS) and homocysteine (Hcy) levels. This study investigated the association between plasma Hcy levels and renal insufficiency in patients with AIS. A total of 987 patients with AIS who had been treated at the First People's Hospital of Foshan between 2011 and 2014 were retrospectively studied. Based on their cystatin C (Cys C) levels, the patients were divided into the normal renal function group (Cys C ≤ 1.25 mg/L) or the renal impairment group (Cys C > 1.25 mg/L). Multivariate regression analysis was applied to reveal the association between hyperhomocysteinemia (HHcy) and renal impairment. The renal impairment group showed more advanced age of onset, higher percentage of prior stroke and hypertension, higher baseline National Institute of Health Stroke Scale score, lower high-density lipoprotein cholesterol levels, and higher Hcy levels compared with the normal renal function group. A multivariate analysis revealed a relationship between early renal impairment and Hcy levels: an increase of Hcy by 1 μmol/L was associated with an increase of 12-18% of the risk of renal impairment among patients with AIS and HHcy. Patients with AIS and HHcy had a 2.42-3.51 fold increase of the risk of renal impairment compared with patients with normal Hcy level (P < 0.001). In conclusion, patients with stroke and HHcy could be more prone to renal impairment.

Association of body mass index, waist circumference, and metabolic syndrome with serum cystatin C in a Chinese population

BACKGROUND

The aim of the study was to evaluate the association of body mass index (BMI), waist circumference (WC), and metabolic syndrome (MetS) with serum cystatin C (CysC) in a Chinese population.

METHODS

The population was composed of 5866 subjects. MetS was diagnosed using the American Heart Association/National Heart, Lung, and Blood Institute 2005 (NCEP-R) criteria. Covariates were analyzed using logistic regression and Spearman partial correlation.

RESULTS

In this population, triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), fasting plasma glucose (FPG), high sensitivity C-reactive protein (hs-CRP), BMI, WC, systolic blood pressure (SBP), diastolic blood pressure (DBP), serum creatinine (Scr), and CysC were significantly higher, and HDL-C and the estimated glomerular filtration rate (Chronic Kidney Disease Epidemiology Collaboration) (eGFRCKD-EPI) were significantly lower in the MetS than in the non-MetS group. TG, LDL-C, FPG, hs-CRP, BMI, WC, SBP, DBP, and Scr were significantly higher, and HDL-C and eGFRCKD-EPI were significantly lower in the 4th quartile than in the 1st quartile of CysC. Logistic regression analysis showed that sex, age, hs-CRP, and CysC were independently associated with the presence of MetS (OR = 3.732, 1.028, 1.051, and 3.334, respectively; P < 0.05). No significant association between the presence of MetS and either Scr or eGFRCKD-EPI was observed. After adjustment for age and sex, BMI, WC, hs-CRP, and Scr were all positively correlated, whereas eGFRCKD-EPI was negatively correlated with CysC (r = 0.029, 0.061, 0.189, 0.227, and -0.210, respectively; P < 0.05).

CONCLUSION

The present study revealed that the CysC was more closely associated with the presence of MetS, as compared Scr or eGFRCKD-EPI. CysC was positively correlated with BMI, and more strongly, positively correlated with WC and inflammation.

Cystatin-C and epicardial adipose tissue as noninvasive predictors of cardiovascular risk in acromegaly

BACKGROUND

Acromegaly (ACRO) is associated with elevated cardiovascular risk, although the prevalence of coronary artery disease (CAD) is unclear. Increased epicardial adipose tissue (EAT) and elevated cystatin-C (Cys-C) levels are cardiovascular risk factors, also related to the progression of CAD in several populations.

AIMS

To measure the severity and extent of CAD in patients with ACRO and to determine whether either EAT or Cys-C reflect higher cardiovascular risk in patients with ACRO than in healthy controls.

SUBJECTS AND METHODS

Case-control study, of 35 patients with ACRO (19 males, 17 with active disease) and 35 age-, gender- and body mass index (BMI)-matched healthy controls; mean age was 48·1 ± 8·1 years and mean BMI was 27·6 ± 4·8 kg/m² . Cys-C was measured by an immunoturbidimetric assay. The 10-year risk of developing a coronary event was calculated using the Framingham Risk Score (FRS). EAT index (volume indexed to body surface area), and severity and extent of CAD were measured using a 256-slice multidetector computed tomography scanner (iCT-256 Philips Healthcare, Amsterdam).

RESULTS

Coronary artery disease lesions, EAT index and severity/extent of CAD were similar between patients with ACRO and controls. Forty-four per cent of patients with ACRO had mild coronary lesions associated with greater EAT index (ß = 0·022, P = 0·036). Cys-C levels correlated with both EAT index (ρ = 0·386, P = 0·031) and FRS (ρ = 0·477, P = 0·004) in patients with ACRO only, despite similar prevalence of traditional cardiovascular risk factors. In a multiple linear regression model, both Cys-C levels (ß = 0·369, P = 0·007) and EAT index (ß = 0·29, P = 0·025) predicted FRS (R² = 0·613).

CONCLUSIONS

In patients with ACRO, both Cys-C and EAT index might be used as noninvasive predictors of cardiovascular risk.

Circulating Angiopoietin-2 and Its Soluble Receptor Tie-2 Concentrations Are Related to Renal Function in Two Population-Based Cohorts

Background

An intact angiopoietin/Tie-2 ligand receptor system is indispensable for life. High circulating angiopoietin-2 (Ang-2) concentrations are strongly associated with kidney disease involving the progressive loss of glomerular filtration. The aim of our study was to investigate the associations between renal function and serum Ang-2 or serum Tie-2 concentrations in the general population.

Methods

Data of 3081 and 4088 subjects from two population-based studies, the Study of Health in Pomerania (SHIP-1) and SHIP-Trend, were used. Renal function was assessed by serum creatinine, cystatin C concentration, creatinine-based estimated glomerular filtration rate [eGFR(crea)], cystatin C-based eGFR [eGFR(cys)] and urinary albumin-to-creatinine ratio (uACR). Analyses of variance and linear regression models were calculated.

Results

In both cohorts, strong positive associations between serum cystatin C concentrations and serum Ang-2 or Tie-2 concentrations as well as inverse associations between eGFR(cys) and serum Ang-2 or Tie-2 concentrations were found. These relations were also present in a subpopulation without hypertension or diabetes mellitus type 2. Furthermore, we detected weak U-shaped associations between serum creatinine concentrations or eGFR(crea) and serum Ang-2 concentrations. With respect to uACR a strong positive association with serum Ang-2 concentrations was revealed.

Conclusion

Serum Ang-2 concentrations are strongly associated with sensitive parameters of renal impairment like serum cystatin C, uACR and eGFR(cys). These findings persisted even after exclusion of subjects with hypertension or diabetes mellitus type 2, conditions that predispose to chronic renal disease and are associated with increased Ang-2 concentrations. Interestingly, we did not detect the same strong relations between serum creatinine and eGFR(crea) with serum Ang-2 concentration. Additionally, significant association of serum Tie-2 concentrations with cystatin C and eGFR(cys) were detected.

Association Between Serum Cystatin C Level and Total Magnetic Resonance Imaging Burden of Cerebral Small Vessel Disease in Patients With Acute Lacunar Stroke

OBJECTIVE

Chronic kidney disease (CKD) is associated with cerebral small vessel disease (cSVD). However, the relationship between serum cystatin C (CysC) level, a highly sensitive marker of impaired kidney function, and cSVD has not been fully understood. This study aimed to investigate the association between serum CysC level and total burden of cSVD on magnetic resonance imaging (MRI) in patients with acute lacunar stroke.

MATERIALS AND METHODS

A total of 210 patients with first-ever acute lacunar stroke occurring within 1 week after onset were included in this study. Serum CysC level, decreased estimated glomerular filtration rate (eGFR), and proteinuria were used to evaluate kidney function. The combined effect of the markers of cSVD on MRI, including lacunar, white matter lesions, cerebral microbleeds, and enlarged perivascular spaces, were used to evaluate the comprehensive cSVD burden.

RESULTS

There is a positive association between total cSVD burden and hypertension, low eGFR level, and serum CysC level. After adjustments for potential confounders by ordinal logistic regression, elevated levels of CysC as well as impaired eGFR and the presence of proteinuria were correlated with the burden of total cSVD (odds ratio [OR] 2.633, 95% confidence interval [CI] 1.284-5.403; OR 2.442, 95% CI 1.213-4.918; and OR 2.151, 95% CI 1.162-3.983, respectively).

CONCLUSIONS

The elevated level of serum CysC is associated with the total burden of cSVD in patients with acute lacunar stroke independent of conventional risk factors.

Cross-sectional study on the relationship between the level of serum cystatin C and blood pressure reverse dipping in hypertensive patients

OBJECTIVE

To investigate the relationship between the level of serum cystatin C (s-CC) and reverse-dipper blood pressure (BP) pattern.

DESIGN

Cross-sectional study.

SETTING

Single centre.

PARTICIPANTS

A total of 718 hypertensive patients were eventually recruited from cardiac clinics between 2012 and 2014 in the Second Affiliated Hospital, Xi'an Jiaotong University. They were diagnosed as essential hypertension according to their casual office records of systolic blood pressure (SBP) and/or diastolic blood pressure (DBP). Patients were excluded if they were <18 or >90 years old, under antihypertensive treatment, night workers, suffering from acute stroke or myocardial infarction within the past 6 months, diagnosed as secondary hypertension, sleep apnoea or other sleep disorders, renal failure, cardiac failure, chronic obstructive pulmonary disease, women during pregnancy or intolerant to the ambulatory BP monitoring (ABPM).

MEASUREMENT

The selected patients were evaluated with 24 hours ABPM. Peripheral venous blood samples were collected to evaluate the s-CC levels by ELISA.

METHODS

The distribution of hypertensive patients with different levels of s-CC among each circadian BP pattern group was analysed using analysis of variance. Multinomial logistic regression analysis was applied to explore the relationship between the relevant variables and ABPM results.

RESULTS

S-CC level in reverse-dipper group (1.19±0.53 mg/L) was increased significantly when compared with dipper group (1.06±0.36 mg/L) (p=0.021). In addition, after multinomial logistic regression analysis, s-CC (OR 1.717; 95% CI 1.033 to 2.854; p=0.037) and diabetes (OR 2.313; 95% CI 1.401 to 3.821; p=0.01) were significantly different between the reverse-dipper group and dipper group. On the other hand, the decline rate of nocturnal SBP (r=-0.117; p=0.002) and DBP (r=-0.089; p=0.018) was negatively correlated with the s-CC level.

CONCLUSIONS

The s-CC level was significantly higher in the reverse-dipper group than the dipper group and that s-CC was associated with the reverse-dipper pattern of BP examined with 24 hour ABPM.

Biomarkers of kidney function and prediction of death from cardiovascular and other causes in the elderly: A 9-year follow-up study

BACKGROUND

Cystatin C is claimed to be superior to creatinine-based estimates of glomerular filtration rate (eGFRcr). The purpose of the study is to analyze whether cystatin C, creatinine, and/or estimated glomerular filtration rates (eGFR) predicted cardiovascular and/or non-cardiovascular deaths among Finnish elderly.

METHODS

Hazard ratios (HR) of cystatin C, creatinine and eGFRs for cardiovascular and non-cardiovascular deaths.

RESULTS

During a 9-year follow-up, 275 died, 192 deaths were a result of cardiovascular disease. In age-adjusted analyses, cystatin C predicted the risk of non-cardiovascular and cardiovascular death in men (HR for 0.1-unit increase 1.12 [95% CI, 1.04-1.19] for non-CVD deaths and 1.18 [1.09-1.28] for CVD deaths) and women (1.14 [1.07-1.21] and 1.14 [1.06-1.22], respectively). CKD-EPIcr-cyc predicted the risk of CVD deaths in men (HR for 5-unit decrease 1.17 [1.09-1.25]) and women (1.09 [1.02-1.17]) and non-CVD deaths in women (1.07 [1.01-1.14]). Also, MDRD (HR for 5-unit decrease 1.16 [1.05-1.27]) and CKD-EPI (HR for 5-unit decrease 1.15 [1.05-1.25]) predicted CVD deaths among men. After additional adjustments, predictive value of cystatin C remained significant. Also, the predictive value of CKD-EPIcr-cys remained significant in non-CVD deaths among women.

CONCLUSION

Cystatin C was clearly the best predictor for cardiovascular and non-cardiovascular deaths among Finnish elderly. Serum cystatin C is more accurate for clinical decision making than creatinine-based eGFR equations or the combined CKD-EPIcr-cys equation in persons older than 64years.

The potential of cystatin-C to evaluate the prognosis of acute heart failure: A comparative study

BACKGROUND

The prognosis of acute heart failure (HF) can be determined by cardio-renal function which is assessed by cystatin-C (Cys-C). We evaluated whether Cys-C could be a more useful prognostic indicator in acute HF, compared with uric acid (UA) and N-terminal pro-B-type natriuretic peptide (NT-proBNP).

METHODS

Two hundred thirty-two HF patients in the emergency room were studied using measurements of Cys-C, UA, and NT-proBNP. During the follow-up, cardiac events, defined as the composites of recurrent HF or cardiac death, were determined.

RESULTS

Seventy-seven cardiac events (28 cardiac deaths, 49 recurrent HFs) occurred over two years. The events group revealed higher levels of Cys-C, UA, and NT-proBNP. They showed increased blood urea nitrogen and creatinine, reduced septal tissue Doppler velocity (TVI-Sm), and low frequencies of beta-blockers (BB), diuretics and angiotensin-converting enzyme inhibitors/-receptor blockers. Cys-C (the best cutoff: 1.7 mg/l) had a steady, persistent hazard ratio (HR) over two years. On multivariate analysis, Cys-C, TVI-Sm, and BB were significant predictors for adverse events. Cys-C provided an incremental value for prognosis more than NT-proBNP and UA did over the follow-up period.

CONCLUSIONS

Compared with UA and NT-proBNP, Cys-C could be better prognostic biomarker for cardiac events two years after acute HF.

Role of renal function in cardiovascular risk assessment: A retrospective cohort study in a population with low incidence of coronary heart disease

BACKGROUND

Early-stage chronic kidney disease (CKD), a marker of cardiovascular risk, is susceptible to therapeutic intervention but need further study in populations with low incidence of coronary heart disease (CHD). Incorporating glomerular filtration rate (GFR) could improve cardiovascular risk prediction in these patients.

OBJECTIVE

To determine if decreased GFR is associated with increased risk of cardiovascular morbidity and all-cause mortality and to analyse GFR effect on cardiovascular risk prediction in a population with low CHD incidence.

METHODS

Retrospective, observational, population-based study of 1,081,865 adults (35-74years old). Main exposure variable: GFR.

OUTCOMES

CHD, cerebrovascular disease, cardiovascular diseases, all-cause mortality. Association between GFR categories of CKD (G1-G5) and outcomes was tested with Cox survival models. G1 was defined as the reference category. Predictive value of GFR was evaluated by integrated discrimination improvement (IDI) and net reclassification improvement (NRI) indices.

RESULTS

Beginning at stage-3a CKD, increased risk was observed for coronary (HR 1.27 (95%CI 1.14-1.43)), cerebrovascular (HR 1.19 (95%CI 1.06-1.34)), cardiovascular (HR 1.23 (95%CI 1.13-1.34)) and all-cause mortality risk (HR 1.17 (95%CI 1.07-1.27)). GFR did not increase discrimination and reclassification indices significantly for any outcome.

CONCLUSION

In general population with low CHD incidence and stage-3 CKD, impaired GFR was associated with increased risk of all cardiovascular diseases studied and all-cause mortality, but adding GFR values did not improve cardiovascular risk calculation. Despite a four-fold higher rate of CHD incidence at GFR G3a compared to G1, this represents moderate cardiovascular risk in our context.

Effects of serelaxin in acute heart failure patients with renal impairment: results from RELAX-AHF

BACKGROUND

Serelaxin showed beneficial effects on clinical outcome and trajectories of renal markers in patients with acute heart failure. We aimed to study the interaction between renal function and the treatment effect of serelaxin.

METHODS

In the current post hoc analysis of the RELAX-AHF trial, we included all patients with available estimated glomerular filtration rate (eGFR) at baseline (n = 1132). Renal impairment was defined as an eGFR <60 ml/min/1.73 m(2) estimated by creatinine.

RESULTS

817 (72.2 %) patients had a baseline eGFR <60 ml/min/1.73 m(2). In placebo-treated patients, baseline renal impairment was related to a higher 180 day cardiovascular (HR 3.12, 95 % CI 1.33-7.30) and all-cause mortality (HR 2.81, 95 % CI 1.34-5.89). However, in serelaxin-treated patients, the risk of cardiovascular and all-cause mortality was less pronounced (HR 1.19, 95 % CI 0.54 -2.64; p for interaction = 0.106, and HR 1.15 95 % CI 0.56-2.34 respectively; p for interaction = 0.088). In patients with renal impairment, treatment with serelaxin resulted in a more pronounced all-cause mortality reduction (HR 0.53, 95 % CI 0.34-0.83), compared with patients without renal impairment (HR 1.30, 95 % CI 0.51-3.29).

CONCLUSION

Renal dysfunction was associated with higher cardiovascular and all-cause mortality in placebo-treated patients, but not in serelaxin-treated patients. The observed reduction in (cardiovascular) mortality in RELAX-AHF was more pronounced in patients with renal dysfunction. These observations need to be confirmed in the ongoing RELAX-AHF-2 trial.

The association of plasma cystatin C proteoforms with diabetic chronic kidney disease

Background

Cystatin C (CysC) is an endogenous cysteine protease inhibitor that can be used to assess the progression of kidney function. Recent studies demonstrate that CysC is a more specific indicator of glomerular filtration rate (GFR) than creatinine. CysC in plasma exists in multiple proteoforms. The goal of this study was to clarify the association of native CysC, CysC missing N-terminal Serine (CysC des-S), and CysC without three N-terminal residues (CysC des-SSP) with diabetic chronic kidney disease (CKD).

Results

Using mass spectrometric immunoassay, the plasma concentrations of native CysC and the two CysC truncation proteoforms were examined in 111 individuals from three groups: 33 non-diabetic controls, 34 participants with type 2 diabetes (DM) and without CKD and 44 participants with diabetic CKD. Native CysC concentrations were 1.4 fold greater in CKD compared to DM group (p = 0.02) and 1.5 fold greater in CKD compared to the control group (p = 0.001). CysC des-S concentrations were 1.55 fold greater in CKD compared to the DM group (p = 0.002) and 1.9 fold greater in CKD compared to the control group (p = 0.0002). CysC des-SSP concentrations were 1.8 fold greater in CKD compared to the DM group (p = 0.008) and 1.52 fold greater in CKD compared to the control group (p = 0.002). In addition, the concentrations of CysC proteoforms were greater in the setting of albuminuria. The truncated CysC proteoform concentrations were associated with estimated GFR independent of native CysC concentrations.

Conclusion

Our findings demonstrate a greater amount of CysC proteoforms in diabetic CKD. We therefore suggest assessing the role of cystatin C proteoforms in the progression of CKD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12953-016-0096-7) contains supplementary material, which is available to authorized users.

Cystatin C as a biomarker for estimating glomerular filtration rate

PURPOSE OF REVIEW

Glomerular filtration rate (GFR) is rarely measured in clinical practice because of the complexity of the measurement. As such, kidney function is typically estimated using validated study equations, which use readily available data including age, sex, race, and serum creatinine as filtration marker. Contemporary research suggests that cystatin C may be an improved alternative to creatinine for inclusion in GFR estimating equations. The purpose of this article is to evaluate the benefits and limitations of using cystatin C as a biomarker of filtration.

RECENT FINDINGS

Cystatin C has fewer non-GFR determinants, when compared with serum creatinine. Use of serum cystatin C avoids the limitations related to both diet and muscle mass that affect serum creatinine. Cystatin C may be more accurate than serum creatinine in estimating GFR, and is more strongly associated with all-cause mortality and cardiovascular events.

SUMMARY

Cystatin C has some advantages over serum creatinine in estimating GFR. The use of cystatin C as a confirmatory biomarker in deciding medication dosages or as a confirmatory test in patients with an uncertain diagnosis of chronic kidney disease may be beneficial.

The description of a method for accurately estimating creatinine clearance in acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is a common and serious condition encountered in hospitalized patients. The severity of kidney injury is defined by the RIFLE, AKIN, and KDIGO criteria which attempt to establish the degree of renal impairment. The KDIGO guidelines state that the creatinine clearance should be measured whenever possible in AKI and that the serum creatinine concentration and creatinine clearance remain the best clinical indicators of renal function. Neither the RIFLE, AKIN, nor KDIGO criteria estimate actual creatinine clearance. Furthermore there are no accepted methods for accurately estimating creatinine clearance (K) in AKI.

STUDY DESIGN

The present study describes a unique method for estimating K in AKI using urine creatinine excretion over an established time interval (E), an estimate of creatinine production over the same time interval (P), and the estimated static glomerular filtration rate (sGFR), at time zero, utilizing the CKD-EPI formula. Using these variables estimated creatinine clearance (Ke)=E/P * sGFR.

SETTING AND PARTICIPANTS

The method was tested for validity using simulated patients where actual creatinine clearance (Ka) was compared to Ke in several patients, both male and female, and of various ages, body weights, and degrees of renal impairment. These measurements were made at several serum creatinine concentrations in an attempt to determine the accuracy of this method in the non-steady state. In addition E/P and Ke was calculated in hospitalized patients, with AKI, and seen in nephrology consultation by the author. In these patients the accuracy of the method was determined by looking at the following metrics; E/P>1, E/P<1, E=P in an attempt to predict progressive azotemia, recovering azotemia, or stabilization in the level of azotemia respectively. In addition it was determined whether Ke<10 ml/min agreed with Ka and whether patients with AKI on renal replacement therapy could safely terminate dialysis if Ke was greater than 5 ml/min.

OUTCOMES AND RESULTS

In the simulated patients there were 96 measurements in six different patients where Ka was compared to Ke. The estimated proportion of Ke within 30% of Ka was 0.907 with 95% exact binomial proportion confidence limits. The predictive accuracy of E/P in the study patients was also reported as a proportion and the associated 95% confidence limits: 0.848 (0.800, 0.896) for E/P<1; 0.939 (0.904, 0.974) for E/P>1 and 0.907 (0.841, 0.973) for 0.9<E/P<1.1. Ke<10 ml/min correlated very well with Ka, while Ke>5 ml/min accurately predicted the ability to terminate renal replacement therapy in AKI.

LIMITATIONS

Include the need to measure urine volume accurately. Furthermore the precision of the method requires accurate estimates of sGFR, while a reasonable measure of P is crucial to estimating Ke.

CONCLUSIONS

The present study provides the practitioner with a new tool to estimate real time K in AKI with enough precision to predict the severity of the renal injury, including progression, stabilization, or improvement in azotemia. It is the author's belief that this simple method improves on RIFLE, AKIN, and KDIGO for estimating the degree of renal impairment in AKI and allows a more accurate estimate of K in AKI.

Relationship between cystatin C and metabolic syndrome among Chinese premenopausal and postmenopausal women without recognized chronic kidney disease

OBJECTIVE

Although studies have shown that elevated cystatin C (Cys-C) levels are associated with the risk of metabolic syndrome (MetS) in the general population, few studies have examined the relationship between serum Cys-C levels and MetS, stratified by menopause status, among women in China. Therefore, we conducted this study to assess the relationship between Cys-C levels and MetS in Chinese premenopausal and postmenopausal women.

METHODS

We performed a cross-sectional analysis of the baseline data of 1,428 Chinese community-dwelling women who participated in the annual health checkup. MetS was defined by the updated National Cholesterol Education Program/Adult Treatment Panel III criteria. Binary logistic regression analysis was performed to estimate the association between Cys-C levels and MetS. One-way analysis of variance, followed by posttest for linear trends, was performed to evaluate the relationships between Cys-C levels and the number of MetS components. Ordinal regression analysis was used to determine whether menopause status and MetS components contribute to elevated levels of Cys-C.

RESULTS

The mean level of Cys-C was significantly higher in women with MetS than in those without MetS among both premenopausal and postmenopausal women, showing a progressive increase (P for trend < 0.001) in parallel with the progressive increment in the number of MetS components in all women. Higher Cys-C levels were found to be associated with the presence of MetS after adjusting for age, body mass index, and estimated glomerular filtration rate in all women. The higher odds ratio changed little, even after further adjustment for serum blood nitrogen, total cholesterol, low-density lipoprotein cholesterol, drinking status, and smoking status. Elevated Cys-C level was significantly associated with postmenopause status (P = 0.007), increased waist circumference (P = 0.006), and elevated blood pressure (P = 0.025).

CONCLUSIONS

Higher serum Cys-C levels are positively and independently associated with the presence of MetS in Chinese premenopausal and postmenopausal women. Elevated Cys-C levels are significantly associated with postmenopause status.

A New Equation to Estimate Muscle Mass from Creatinine and Cystatin C

Background

With evaluation for physical performance, measuring muscle mass is an important step in detecting sarcopenia. However, there are no methods to estimate muscle mass from blood sampling.

Methods

To develop a new equation to estimate total-body muscle mass with serum creatinine and cystatin C level, we designed a cross-sectional study with separate derivation and validation cohorts. Total body muscle mass and fat mass were measured using dual-energy x-ray absorptiometry (DXA) in 214 adults aged 25 to 84 years who underwent physical checkups from 2010 to 2013 in a single tertiary hospital. Serum creatinine and cystatin C levels were also examined.

Results

Serum creatinine was correlated with muscle mass (P < .001), and serum cystatin C was correlated with body fat mass (P < .001) after adjusting glomerular filtration rate (GFR). After eliminating GFR, an equation to estimate total-body muscle mass was generated and coefficients were calculated in the derivation cohort. There was an agreement between muscle mass calculated by the novel equation and measured by DXA in both the derivation and validation cohort (P < .001, adjusted R² = 0.829, β = 0.95, P < .001, adjusted R² = 0.856, β = 1.03, respectively).

Conclusion

The new equation based on serum creatinine and cystatin C levels can be used to estimate total-body muscle mass.

The Association of Serum Cystatin C with Glycosylated Hemoglobin in Korean Adults

BACKGROUND

Cystatin C has been known to be associated not only with early renal impairment but also with the incidence of diabetic conditions (prediabetes plus diabetes). However, it is not clear whether cystatin C levels are associated with the prevalence of diabetic conditions in Asian populations. We evaluated this association using glycosylated hemoglobin (HbA1c) levels as the definition of diabetes in Korean adults.

METHODS

We analyzed data from 1,559 Korean adults (937 men and 622 women) with available serum cystatin C and HbA1c values.

RESULTS

The serum cystatin C levels in subjects with prediabetes and diabetes were significantly increased (0.91±0.14 mg/L in prediabetes and 0.91±0.17 mg/L in diabetes vs. 0.88±0.13 mg/L in patients with normal glucose levels, P=0.001). At increasing cystatin C levels, the prevalence of subjects with prediabetes (30.2% vs. 14.6%, P<0.001) and those with diabetes (10.6% vs. 8.0%, P<0.001) significantly increased in the group with the highest cystatin C levels. The group with the highest cystatin C levels had a significantly increased odds ratio (OR) for the presence of diabetic conditions compared to the group with the lowest values in total subjects (OR, 2.35; 95% confidence interval [CI], 1.54 to 3.58; P<0.001) and in women (OR, 4.13; 95% CI, 1.97 to 8.65; P<0.001), though there was no significant increase after adjusting for multiple variables.

CONCLUSIONS

Higher levels of serum cystatin C are associated with an increased prevalence of diabetic conditions in Korean adults. Our findings may extend the positive association of cystatin C with diabetes incidence to an Asian population.

Biomarkers of Metabolic Syndrome: Biochemical Background and Clinical Significance

Biomarkers of the metabolic syndrome are divided into four subgroups. Although dividing them in groups has some limitations, it can be used to draw some conclusions. In a first part, the dyslipidemias and markers of oxidative stress are discussed, while inflammatory markers and cardiometabolic biomarkers are reviewed in a second part. For most of them, the biochemical background and clinical significance are discussed, although here also a well-cut separation cannot always be made. Altered levels cannot always be claimed as the cause, risk, or consequence of the syndrome. Several factors are interrelated to each other and act in a concerted, antagonistic, synergistic, or modulating way. Most important conclusions are summarized at the end of every reviewed subgroup. Genetic biomarkers or influences of various food components on concentration levels are not included in this review article.

Can admission serum cystatin C level be an early marker subclinical acute kidney injury in critical care patients?

BACKGROUND

In critical care patients, the diagnosis of subclinical acute kidney injury (AKI) might be difficult with measurements of serum creatinine and estimated glomerular filtration rate (eGFR). Their 'sensitive kidneys' can easily be affected from sepsis, underlying diseases, medications and volume status and if they can be detected earlier, some preventive measures might be taken. In this study we aimed to determine whether admission serum cystatin C (sCys-C) and other clinical parameters can identify subclinical AKI in medical intensive care unit (ICU) patients with normal creatinine-based eGFR at admission.

METHODS

A prospective cohort study, performed in an adult ICU of a university hospital between January 2008 and March 2013. The blood samples were obtained within the first 24-48 hours of admission and sCys-C levels were analyzed with particle-enhanced immunonephelometric assay. AKI development was assessed according to RIFLE criteria. The cutoff value of sCys-C for the prediction of AKI was determined with receiver operating characteristic (ROC) curve analysis.

RESULTS

A total of 72 patients were included in the study and 19 (26%) of them developed AKI. Among the patients with AKI admission sCys-C levels were significantly higher when compared with non-AKI patients (1.06 ± 0.29 vs. 0.89 ± 0.28 respectively, p = 0.026). With ROC curve analysis, the threshold level for sCys-C was 0.94 mg/L with 63% sensitivity and 66% specificity [AUC: 0.67, p = 0.026]. With logistic regression analysis 'high sCys-C levels at admission' (OR = 4.73; 95%CI 1.03-21.5, p = 0.044) was found as one of the independent variables for the prediction of AKI development, in addition to 'being intubated before ICU admission' (OR = 10.2; 95%CI 1.72-60.4, p = 0.01) and 'hypotension during ICU follow-up' (OR = 12.3; 95%CI 2.5-60.1, p = 0.002).

CONCLUSION

In this cohort of patients, a high sCys-C level at admission was found to be a predictor of subclinical AKI arising during their ICU stay. If supported with further studies, it might be used to provide more accurate and earlier knowledge about renal dysfunction and to take appropriate preventive measures.

Proteinuria and Albuminuria During and After Paricalcitol Treatment in Chronic Kidney Disease Patients

Data on paricalcitol lowering albuminuria and proteinuria already exist; however, it is unclear how paricalcitol withdrawal affects both. Forty-two nondialysis chronic kidney disease (CKD) patients (29 men) aged 62.3 ± 12 years completed the study. CKD patients with proteinuria and intact parathyroid hormone ≥65 pg/mL received paricalcitol (1 μg/day po) for 6 months. After paricalcitol withdrawal we followed them for 6 more months. Paricalcitol treatment significantly reduced urinary albumin/creatinine ratio (UACR), 24-hour albuminuria (24hA), and 24-hour proteinuria (24hP). Six months after drug withdrawal UACR increased significantly, 24hA and 24hP did not change significantly. Serum creatinine and cystatin C significantly increased during treatment, and estimated glomerular filtration rate (eGFR) decreased. After drug withdrawal serum creatinine, cystatin C, and eGFR did not change significantly. In conclusion, 6-month paricalcitol treatment (1 μg/day) in nondialysis CKD patients significantly reduced albuminuria and proteinuria. Six months after paricalcitol withdrawal 24hA and 24hP did not change significantly. Kidney function decreased during paricalcitol treatment; after paricalcitol withdrawal it remained stable. The unaltered values of 24hA, 24hP, and kidney function after paricalcitol withdrawal could be a delayed effect of paricalcitol treatment.

Plasma Levels of Middle Molecules to Estimate Residual Kidney Function in Haemodialysis without Urine Collection

Background

Residual Kidney Function (RKF) is associated with survival benefits in haemodialysis (HD) but is difficult to measure without urine collection. Middle molecules such as Cystatin C and β2-microglobulin accumulate in renal disease and plasma levels have been used to estimate kidney function early in this condition. We investigated their use to estimate RKF in patients on HD.

Design

Cystatin C, β2-microglobulin, urea and creatinine levels were studied in patients on incremental high-flux HD or hemodiafiltration(HDF). Over sequential HD sessions, blood was sampled pre- and post-session 1 and pre-session 2, for estimation of these parameters. Urine was collected during the whole interdialytic interval, for estimation of residual GFR (GFR_Residual = mean of urea and creatinine clearance). The relationships of plasma Cystatin C and β2-microglobulin levels to GFR_Residual and urea clearance were determined.

Results

Of the 341 patients studied, 64% had urine output>100ml/day, 32.6% were on high-flux HD and 67.4% on HDF. Parameters most closely correlated with GFR_Residual were 1/β2-micoglobulin (r² 0.67) and 1/Cystatin C (r² 0.50). Both these relationships were weaker at low GFR_Residual. The best regression model for GFR_Residual, explaining 67% of the variation, was: GFRResidual=160.3⋅(1β2m)−4.2 Where β2m is the pre-dialysis β2 microglobulin concentration (mg/L). This model was validated in a separate cohort of 50 patients using Bland-Altman analysis. Areas under the curve in Receiver Operating Characteristic analysis aimed at identifying subjects with urea clearance≥2ml/min/1.73m² was 0.91 for β2-microglobulin and 0.86 for Cystatin C. A plasma β2-microglobulin cut-off of ≤19.2mg/L allowed identification of patients with urea clearance ≥2ml/min/1.73m² with 90% specificity and 65% sensitivity.

Conclusion

Plasma pre-dialysis β2-microglobulin levels can provide estimates of RKF which may have clinical utility and appear superior to cystatin C. Use of cut-off levels to identify patients with RKF may provide a simple way to individualise dialysis dose based on RKF.

Biomarkers of renal injury and function: diagnostic, prognostic and therapeutic implications in heart failure

Heart failure guidelines suggest evaluating renal function as a routine work-up in every patient with heart failure. Specifically, it is advised to calculate glomerular filtration rate and determine blood urea nitrogen. The reason for this is that renal impairment and worsening renal function (WRF) are common in heart failure, and strongly associate with poor outcome. Renal function, however, consists of more than glomerular filtration alone, and includes tubulointerstitial damage and albuminuria. For each of these renal entities, different biomarkers exist that have been investigated in heart failure. Hypothetically, and in parallel to data in nephrology, these markers may aid in the diagnosis of renal dysfunction, or for risk stratification, or could help in therapeutic decision-making. However, as reviewed in the present manuscript, while these markers may carry prognostic information (although not always additive to established markers of renal function), their role in predicting WRF is limited at best. More importantly, none of these markers have been evaluated as a therapeutic target nor have their serial values been used to guide therapy. The evidence is most compelling for the oldest-serum creatinine (in combination with glomerular filtration rate)-but even for this biomarker, evidence to guide therapy to improve outcome is circumstantial at best. Although many new renal biomarkers have emerged at the horizon, they have only limited usefulness in clinical practice until thoroughly and prospectively studied. For now, routine measurement of (novel) renal biomarkers can help to determine cardiovascular risk, but there is no role for these biomarkers to change therapy to improve clinical outcome in heart failure.

Biomarkers of Renal Function in Type 2 Diabetic Patients with Cognitive Impairment

Kidney disease is associated with cognitive impairment in studies of nondiabetic adults. We examined the cross-sectional relation between three measures of renal function and cognitive impairment (CI) in type 2 diabetic patients. A total of 357 patients with type 2 diabetes were prospectively enrolled. There were 108 patients with CI and 249 patients without CI (control). We calculated the urinary albumin/creatinine ratio (UACR) from morning spot urine and the estimated glomerular filtration rate (eGFR) in serum samples. Serum Cystatin C (Cys C) was measured with an automated particle-enhanced turbidimetric immunoassay. UACR and Cystatin C levels were significantly higher in patients with CI than those without CI (P<0.001), and the eGFR was lower in patients with CI than those without (P=0.003). A logistic regression analysis indicates that kidney impairment biomarkers levels were significantly associated with an increased risk of CI after adjustment for age and gender. The OR of each kidney biomarker (eGFR, UACR, Cystatin C) for CI status was 1.78 (0.89-3.27), 2.36 (1.29-4.42), and 2.77 (1.36-5.97), respectively. Among three kidney biomarkers (eGFR, UACR, Cystatin C), only elevated serum Cystatin C was associated with increased risk of CI in type 2 diabetic patients, with an OR of 1.42 (1.25-4.24) after additional adjustment for duration of diabetes, hypertension, hyperlipidemia, hemoglobin A1c (HbA1c), high-sensitivity C-reactive protein (Hs-CRP), intima-media thickness (IMT), ankle brachial index (ABI), and brachial-ankle pulse wave velocity (ba-PWV). Furthermore, combination of conventional risk factors and Cystatin C levels exhibited a fair diagnostic value for CI, with an area under the curve (AUC) of 0.91. Among three kidney impairment biomarkers (eGFR, UACR, Cystatin C), only elevated serum Cystatin C was associated with increased risk of CI in type 2 diabetic patients, independent of conventional risk factors. Furthermore, Cystatin C may be a better marker for CI than eGFR and UACR, and exhibited diagnostic value.

Cystatin C: A prognostic marker after myocardial infarction in patients without chronic kidney disease

Aims

Cystatin C is an endogenous marker of renal function. It is a well established better marker of glomerular filtration rate than serum creatinine. There is also evidence that cystatin C is associated with atherosclerotic disease. The present prospective study evaluated the prognostic value of cystatin C after myocardial infarction in patients without chronic kidney disease.

Methods and results

A total of 127 patients who underwent coronary angiography after an acute coronary syndrome (ACS) were included. Cystatin C was associated with the severity of coronary artery disease (CAD). Cystatin C levels were significantly higher in patients with 3-vessels disease and severe CAD according to GENSINI score (p = 0.01 and p < 0.001 respectively). Among the patients admitted for ST elevation myocardial infarction, Cystatin C concentration was correlated with the initial TIMI flow in the culprit artery (p < 0.001). Mean duration of the follow-up period was 10.76 ± 2.1 months. High Cystatin C concentrations were associated to the occurrence of unfavourable outcomes and cardiovascular mortality during follow-up (1.19 ± 0.4 vs. 1.01 ± 0.35 mg/L, p = 0.01 and 1.21 ± 0.36 vs. 0.96 ± 0.27 mg/L, p = 0.03). Among different laboratory parameters, cystatin C was the best marker to predict the occurrence of major adverse cardiovascular events during the follow-up (Area under the receiveroperating characteristic curve = 0.743).

Conclusion

High cystatin C levels are associated with the severity of coronary artery disease in patients presenting an acute coronary syndrome and a normal renal function. Cystatin C is also associated to unfavourable cardiovascular outcomes during follow-up and appears as a strong predictor for risk of cardiovascular events and death.

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.

Prevalence of chronic kidney diseases in patients with chronic obstructive pulmonary disease: assessment based on glomerular filtration rate estimated from creatinine and cystatin C levels

Background

Cardiovascular diseases, osteoporosis, and depression are identified comorbidities of chronic obstructive pulmonary disease (COPD), but there have been few reports of chronic kidney disease (CKD) as a comorbidity of COPD. The objective of this study was to investigate the prevalence of CKD in COPD patients using estimated glomerular filtration rate (eGFR) based on creatinine (Cr) and cystatin C (Cys) levels.

Methods

The prevalence of CKD and the values of various CKD-related parameters were compared between 108 stable COPD outpatients (COPD group) and a non-COPD control group consisting of 73 patients aged 60 years or more without a history of COPD or kidney disease. CKD was defined as an eGFR less than 60 mL/min/1.73 m².

Results

The Cr level was significantly higher in the COPD group, but eGFR based on serum Cr (eGFR_Cr) was not significantly different between the two groups (73.3±25.3 vs 79.7±15.5 mL/min/1.73 m²). The Cys level was significantly higher and eGFR based on serum Cys (eGFR_Cys) was significantly lower in the COPD group (60.0±19.4 vs 74.0±13.5 mL/min/1.73 m², P<0.0001). The prevalence of CKD evaluated based on eGFR_Cr was 31% in the COPD group and 8% in the non-COPD group with an odds ratio of 4.91 (95% confidence interval, 1.94–12.46, P=0.0008), whereas the evaluated prevalence based on eGFR_Cys was 53% in the COPD group and 15% in the non-COPD group with an odds ratio of 6.30 (95% confidence interval, 2.99–13.26, P<0.0001), demonstrating a higher prevalence of CKD when based on eGFR_Cys rather than on eGFR_Cr.

Conclusion

CKD is a comorbidity that occurs frequently in COPD patients, and we believe that renal function in Japanese COPD patients should preferably be evaluated based not only on Cr but on Cr in combination with Cys.

Comparison of Cystatin C and β-Trace Protein Versus 99mTc-DTPA Plasma Sampling in Determining Glomerular Filtration Rate in Chronic Renal Disease

Glomerular filtration rate (GFR) is the best indicator of renal function. The gold standard for GFR measurement is inulin clearance. However, its measurement is inconvenient, time-consuming, and costly. Thus, in both scientific studies and routine clinical practice nuclear medicine methods ((99m)Tc-diethylenetriaminepentaacetic acid [(99m)Tc-DTPA] and (51)Cr-ethylenediaminetetraacetic acid [(51)Cr-EDTA]) are preferred, and they correlate strongly with inulin clearance. In addition, cystatin C and β-trace protein have also recently been used for this purpose. In the literature, however, data are limited about the clinical value of cystatin C and β-trace protein in GFR measurement in chronic renal disease (CRD), and the results have been inconclusive. In this study, we aimed to determine the efficiency of cystatin C and β-trace protein in the determination of GFR in CRD patients.

METHODS

Eighty-four patients with CRD were included in the study (59 men and 25 women; age range, 21-88 y; mean age, 61 y). GFR was calculated using the gold-standard (99m)Tc-DTPA 2-sample plasma sampling method (TPSM) and 2 alternative methods: a formula using cystatin C and a formula using β-trace protein. The correlation between TPSM and the cystatin C and β-trace protein methods was assessed, and Bland-Altman analysis was used to graph scatterplots of the differences at a confidence interval of 95% (mean difference ± 1.96 SDs).

RESULTS

GFRs calculated using both alternative methods correlated strongly with those calculated using the gold standard. However, the correlation was stronger for the cystatin C method than for the β-trace protein method, and neither method produced reliably consistent GFRs.

CONCLUSION

This study demonstrated that cystatin C and β-trace protein do not reflect GFR with sufficient accuracy.

Serum Cystatin C for the Diagnosis of Acute Kidney Injury in Patients Admitted in the Emergency Department

BACKGROUND

Early diagnosis of acute kidney injury (AKI) at emergency department (ED) is a challenging issue. Current diagnostic criteria for AKI poorly recognize early renal dysfunction and may cause delayed diagnosis. We evaluated the use of serum cystatin C (CysC) for the early and accurate diagnosis of AKI in patients hospitalized from the ED.

METHODS

In a total of 198 patients (105 males and 93 females), serum CysC, serum creatinine (sCr), and estimated glomerular filtration rate (eGFR) were calculated at 0, 6, 12, 24, 48, and 72 hours after presentation to the ED. We compared two groups according to the presence or absence of AKI.

RESULTS

Serial assessment of CysC, sCr, and eGFR was not a strong, reliable tool to distinguish AKI from non-AKI. CysC > 1.44 mg/L at admission, both alone (Odds Ratio = 5.04; 95%CI 2.20-11.52; P < 0.0002) and in combination with sCr and eGFR (Odds Ratio = 5.71; 95%CI 1.86-17.55; P < 0.002), was a strong predictor for the risk of AKI.

CONCLUSIONS

Serial assessment of CysC is not superior to sCr and eGFR in distinguishing AKI from non-AKI. Admission CysC, both alone and in combination with sCr and eGFR, could be considered a powerful tool for the prediction of AKI in ED patients.

A Study of the Applicability of GFR Evaluation Equations for an Elderly Chinese Population

OBJECTIVES

This study screened current GFR evaluation equations that showed high accuracy for elderly populations and evaluated the applicability of these equations for an elderly Chinese population.

MEASUREMENTS

A standard dual plasma sampling method (DPSM) of estimating 99mTc-diethylene triamine penta-acetic acid clearance was used to determine measured GFR (mGFR).

RESULTS

Comprehensive information was received for a total of 151 elderly individuals, with a mean mGFR of 65.39 ± 24.19 ml/min/1.73 m2. For the overall samples, the accuracy (P30), bias, absolute bias and interquartile ranges (IQRs) of the CKD2 (cystatin C(CysC)-serum creatinine(SCr)), CKD-EPI(CysC-SCr), Cockcroft-Gault(CG), CKD2(CysC), CKD-EPI(CysC), and Hoek equations were superior to c-aGFR3, c-aGFR4 and Grubb equation, Bland-Altman analysis also demonstrated a consistent result. Among elderly subjects with mGFR≥60 ml/min/1.73 m2, the CKD2 (CysC-SCr) and CKD-EPI (CysC-SCr) equations showed significantly higher correlations and accuracy than the other examined equations. Among elderly subjects with mGFR<60 ml/min/1.73 m2, only the CG equation showed an accuracy (P30) of greater than 70% and demonstrated higher precision than the other examined equations.

CONCLUSION

For the elderly population, the CG, CKD2, CKD-EPI, and Hoek equations exhibited good accuracy. The CKD2(CysC-SCr) equation and CKD-EPI(CysC-SCr) equation demonstrated relatively high accuracy for evaluating elderly subjects with mGFR≥60 ml/min/1.73 m2, whereas the CG equation was more suitable for evaluating elderly subjects with mGFR<60 ml/min/1.73 m2.

Diagnostic and prognostic value of serum cystatin C in critically ill children with acute kidney injury

OBJECTIVES

We aimed to evaluate the value of serum cystatin C for detection of acute kidney injury and pediatric Risk, Injury, Failure, Loss, End-Stage Renal Disease categories in critically ill children and to investigate whether serum cystatin C was associated with outcome.

DESIGN

Prospective cohort study.

SETTING

PICU of a tertiary-care university hospital.

PATIENTS

A heterogeneous population of critically ill children.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Blood and 24-hour urine samples were collected daily over the first 2 days after PICU admission for measurement of serum cystatin C, serum creatinine, and creatinine clearance. Acute kidney injury was classified by pediatric Risk, Injury, Failure, Loss, End-Stage Renal Disease criteria. One hundred twenty-two children were prospectively enrolled; 40 (32.8%) developed acute kidney injury. Serum cystatin C was higher in patients with acute kidney injury compared with those who did not develop acute kidney injury at PICU admission (median, 0.90 mg/L vs 0.51 mg/L) and on the first (1.12 mg/L vs 0.57 mg/L) and second PICU days (1.15 mg/L vs 0.58 mg/L). Serum creatinine was higher in acute kidney injury group only on the first (0.50 mg/dL vs 0.40 mg/dL) and second PICU days (0.60 mg/dL vs 0.40 mg/dL). Serum cystatin C was increasingly higher according to acute kidney injury severity (Failure > Injury > Risk). Area under the receiver operating characteristic curve of cystatin C for acute kidney injury detection was 0.89. Serum cystatin C greater than 0.70 mg/L was associated with longer length of PICU stay (adjusted hazard ratio, 1.64) and prolonged duration of mechanical ventilation (adjusted hazard ratio, 1.82).

CONCLUSIONS

Cystatin C is an early and accurate biomarker for acute kidney injury and pediatric Risk, Injury, Failure, Loss, End-Stage Renal Disease categories, and it is associated with adverse clinical outcomes in a heterogeneous population of critically ill children.

Associations between biomarkers of renal function with cerebral microbleeds in hypertensive patients

BACKGROUND

Cerebral microbleeds (CMBs) have been observed in the elderly and have been regarded as a manifestation of small vessel disease (SVD). Cerebral and glomerular SVD may have a common source of pathogenesis because these organs are closely connected through anatomic and hemodynamic similarities. The purpose of this study was to clarify the associations between kidney biomarker levels and CMBs in hypertensive patients.

METHODS

The presence and number of CMBs were assessed on susceptibility-weighted imaging. We calculated the urinary albumin/creatinine ratio (UACR) from morning spot urine and the estimated glomerular filtration rate (eGFR) in serum samples. Serum cystatin C (CysC) was measured with an automated particle-enhanced turbidimetric immunoassay.

RESULTS

UACR and CysC levels were higher in the patients with CMBs than those without, and the eGFR was lower in the patients with CMBs than those without. A logistic regression analysis indicates that eGFR and UACR were independently associated with the prevalence of deep or infratentorial CMBs. The odds ratio (OR) (95% confidence interval (CI)) of eGFR and UACR was 1.95 (1.37-3.27) and 2.25 (1.66-4.46), respectively. CysC was independently associated with CMBs in both deep or infratentorial and lobar locations. The ORs (95% CI) were 2.59 (1.57-6.22) and 1.57 (1.15-4.85), respectively. Furthermore, CysC exhibited fair diagnostic value for CMBs, with an area under the curve of 0.80.

CONCLUSIONS

Kidney biomarker levels are associated with the presence of CMB in hypertensive patients without a history of transient ischemic attack (TIA) or stroke, independent of conventional risk factors, and CysC was a better marker for CMBs than eGFR and UACR.

Cystatin C as a potential biomarker for dosing of renally excreted drugs

The objective of the present study was to review the available pharmacokinetic evidence for the utility of cystatin C (CysC) as a marker of renal function to predict the dose of renally excreted drugs.The bibliographic search used PubMed and EMBASE databases, from its inception through to January 2014, with the following keywords 'pharmacokinetics' and 'cystatin C'.Sixteen pharmacokinetic publications were identified and seven drugs primarily excreted by the kidney were studied. Among them, only one study was performed in children, the others were performed in adults and/or elderly subjects, either healthy volunteers or patients with variable clinical conditions, such as cystic fibrosis and cancer. Most of studies (n = 13/16) demonstrated that CysC was better correlated with clearance/trough concentration of evaluated drugs compared with creatinine.Our review supports that CysC is a good marker of renal function to predict dose of renally excreted drugs. Efforts should be made to evaluate the impact of CysC in special populations in order to define its clinical value in dosing optimization.

Cystatin C, Beta2 Microglobulin, N-Acetyl-beta-D-glucosaminidase, Retinol-Binding Protein, and Endothelin 1 Levels in the Evaluation of Sickle Cell Disease Nephropathy

OBJECTIVES

Renal involvement is common in sickle cell disease (SCD). Early demonstration of renal injury and commencement of appropriate treatment will increase survival and quality of life in these patients. We investigated renal manifestations in our pediatric and adult SCD patients and evaluated the role of cystatin C, Beta2 microglobulin (B2M), retinol-binding protein (RBP), N-acetyl-beta-D-glucosaminidase (NAG), and endothelin-1 (ET-1) to indicate renal damage.

METHODS

The study involved 45 pediatric and 10 adult patients with SCD and 20 healthy children and 10 healthy adults as a control. All the patients were questioned for possible renal manifestations. 24-hour urine samples were collected and glomerular filtration rates (GFRs) were calculated by using creatinine (GFR(creatinine)), Schwartz formula (GFR(Schwartz)), and cystatin C (GFR(cystatin C)). Blood and urine samples were collected and serum cystatin C, urine B2M, RBP, NAG, and ET-1 levels were measured.

RESULTS

Nocturnal enuresis and proteinuria were the most common renal manifestations in SCD patients. When the groups were compared in terms of GFR, GFR(creatinine) and GFR(Schwartz) levels were higher in group 1 and 2 patients than in control 1 and 2 patients (P < .05). Cystatin C, B2M, RBP, NAG, and ET-1 values were normal in both the patient and the control groups. However, B2M/creatinine levels were higher than 160 μg/mg creatinine levels in 10 patients.

CONCLUSIONS

Serum cystatin C, urine NAG, RBP, and ET-1 levels were found to be insufficient for the evaluation of SCD nephropathy. Increased B2M/creatinie levels can be valuable in estimating possible glomerular and tubular damage in SCD.

Can cystatin C become an easy and reliable tool for anesthesiologists to calculate glomerular filtration rate?

Background and Aims:

The aim was to evaluate the role of cystatin C as a noninvasive and easy marker of glomerular filtration rate (GFR) estimation in voluntary kidney donors.

Materials and Methods:

We retrospectively evaluated 40 voluntary kidney donors. They underwent complete biochemical and nuclear tests as a part of transplant workup. Serum cystatin C, serum creatinine, and Tc-99m diethylene-triamine-penta-acetic acid (DTPA) were used in our study. We calculated GFR using the chronic kidney disease epidemiology collaboration (CKD-EPI) formula based on creatinine only (GFR-CKD-EPI-creat), CKD-EPI formula using creatinine and cystatin C (GFR-CKD-EPI-cyst-creat), and modification of diet in renal disease (MDRD) and CKD-EPI cystatin C equation (2012) (GFR-cyst).

Data was evaluated using the SPSS software (version 11.5). The correlation analysis and analysis of variance was used for statistical computation. Agreement was determined using analyze-it version 2.30 for MS-Excel 12+.

Results:

The mean age of the donors in our study was 49.83 ± 13.06. The mean cystatin C in females was 0.72 ± 0.12, the mean cystain C in males was 0.87 ± 0.23. On correlating GFR-cyst with GFR-DTPA the Pearson correlation coefficient (ρ) was found to be 0.388 this correlation was significant with P < 0.05. While comparing with DTPA the correlation coefficient of GFR-CKD-EPI-creat group was 0.587 which was significant with P < 0.01. The correlation coefficient of GFR-CKD-EPI-cyst-creat group compared with GFR-DTPA group was 0.543 which was also significant at P < 0.001. GFR-CKD-EPI-creat gave the highest correlation with DTPA in our study. The correlation coefficient of GFR-MDRD group with DTPA group was 0.576 this correlation was also significant with P < 0.01. The results obtained were further statistically analyzed by Bland-Altman analysis the percentage error for GFR-DTPA versus GFR-cyst-creat is 29.72%; for GFR-DTPA versus GFR-EPI-creat is 30.73%; or GFR-DTPA versus MDRD is 31.63% and for GFR-DTPA versus GFR-cyst is 34.37%.

Conclusion:

Cystatin C is a good endogenous marker for calculating GFR as it correlates very well with DTPA and CKD-EPI equation based GFR.

A comparison of the effects of ketamine and remifentanil on renal functions in coronary artery bypass graft surgery

We have investigated the effects of ketamine-based and remifentanil-based anesthetic protocol on perioperative serum cystatin-C levels, and creatinine and/or cystatin-C-based eGFR equations in terms of acute kidney injury in coronary artery bypass graft (CABG) surgery. Using a simple randomization method (coin tossing), patients were divided into the two groups and not-blinded to the anesthetist. Remifentanil-midazolam-propofol or ketamine-midazolam-propofol-based anesthetic regimen was chosen. Different eGFR formulas using creatinine (MDRD, CKD-EPI, Cockrauft Gault); cystatin-C (eGFR1, eGFR2) or a combination of creatinine and cystatin-C (eGFR 3) were used to calculate estimated glomerular filtration rates (eGFRs). High-sensitive troponin T was used to determine if ketamine use in coronary surgery contributed to myocardial cell damage. Thirty-seven patients were included in the study (remifentanil group = 19, ketamine Group = 18). Urea, creatinine, cystatin-C levels were comparable between the groups in all the measurement times and also postoperative day 2 samples showed statistically higher results compared to baseline (p < 0.001). Effects of ketamine and remifentanil on renal functions were found similar. Creatinine and cystatin-C-based eGFR equations resulted similar in our study. Reversible stage 1 acute kidney injury (AKI) was observed on postoperative day 2 in seven patients from the remifentanil group and six patients from the ketamine group. Hs-troponin T was found to be higher in postoperative day 1 samples; there were no significant difference between the groups. Our results indicated that patients who have normal renal functions undergoing on-pump coronary bypass surgery, effects of ketamine and remifentanil on renal functions in terms of AKI were found to be similar.

Cystatin C-based CKD-EPI equations and N-terminal pro-B-type natriuretic peptide for predicting outcomes in acutely decompensated heart failure

BACKGROUND

In patients with acute decompensated heart failure (ADHF), both natriuretic peptides and renal impairment predict adverse outcomes. Our aim was to evaluate the complementary prognosis role of N-terminal pro-B-type natriuretic peptide (NT-proBNP) and the newly developed Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations based on cystatin C (CysC) for glomerular filtration rate (GFR) estimation in ADHF patients.

HYPOTHESIS

Renal impairment assessed by CysC-based CKD-EPI equations and natriuretic peptides have complementary prognostic value in ADHF patients.

METHODS

The study included 613 consecutive patients presenting with ADHF. At admission, plasma levels of NT-proBNP and CysC were determined. The GFR was estimated using CysC-based CKD-EPI equations. The primary endpoint was death from any cause and heart failure readmission.

RESULTS

During the median follow-up of 365 days (interquartile range, 227-441 days), 323 patients (0.65 %patient-year) died or were readmitted for heart failure. After multivariate adjustment, estimated GFR <60 mL/min/1.73 m(2) and NT-proBNP >3251 pg/mL were independent predictors of adverse outcomes (P < 0.01). The combination of GFR <60 mL/min/1.73 m(2) and NT-proBNP >3251 pg/mL was associated with the highest risk of adverse outcomes. Furthermore, reclassification analyses demonstrated that use of both NT-proBNP and CysC-based CKD-EPI equations resulted in improving the accuracy for adverse outcomes prediction.

CONCLUSIONS

In patients with ADHF, the combination of NT-proBNP with estimated GFR using CysC-based CKD-EPI equations better predicts outcomes than either parameter alone and adds valuable complementary prognosis information to other established risk factors.

Renal effects of the angiotensin receptor neprilysin inhibitor LCZ696 in patients with heart failure and preserved ejection fraction

BACKGROUND

Increases in serum creatinine with renin-angiotensin-aldosterone system (RAAS) inhibitors can lead to unnecessary discontinuation of these agents. The dual-acting angiotensin receptor neprilysin inhibitor LCZ696 improves clinical outcome patients with heart failure with reduced ejection fraction, and pilot data suggest potential benefit in heart failure with preserved ejection fraction (HFpEF). The effects of LCZ696 on renal function have not been assessed.

METHODS AND RESULTS

A total of 301 HFpEF patients were randomly assigned to LCZ696 or valsartan in the PARAMOUNT trial. We studied renal function [creatinine, estimated glomerular filtration rate (eGFR), cystatin C, and urinary albumin to creatinine ratio (UACR)] at baseline, 12 weeks, and after 36 weeks of treatment. Worsening renal function (WRF) was determined as an serum creatinine increase of >0.3 mg/dL and/or >25% between two time-points. Mean eGFR at baseline was 65.4 ± 20.4 mL/min per 1.73 m(2) . The eGFR declined less in the LCZ696 group than in the valsartan group (-1.5 vs. -5.2 mL/min per 1.73 m(2) ; P = 0.002). The incidence of WRF was lower in the LCZ696 group (12%) than in the valsartan group (18%) at any time-point, but this difference was not statistically significant (P = 0.18). Over 36 weeks, the geometric mean of UACR increased in the LCZ696 group (2.4-2.9 mg/mmol), whereas it remained stable in the valsartan group (2.1-2.0 mg/mmol; P for difference between groups = 0.016).

CONCLUSION

In patients with HFpEF, therapy with LCZ696 for 36 weeks was associated with preservation of eGFR compared with valsartan therapy, but an increase in UACR.