Serum cystatin C level as a potentially good marker for impaired kidney function

The estimation of glomerular filtration in acute and critical illness: Challenges and opportunities

Recent events have made it apparent that the creatinine based estimating equations for glomerular filtration have their flaws. Some flaws have been known for some time; others have prompted radical modification of the equations themselves. These issues persist in part owing to the behaviour of the creatinine molecule itself, particularly in acute and critical illness. There are significant implications for patient treatment decisions, including drug and fluid therapies and choice of imaging modality (contrast vs. non-contrast CT scan for example). An alternative biomarker, Cystatin C, has been used with some success both alone and in combination with creatinine to help improve the accuracy of particular estimating equations. Problems remain in certain circumstances and costs may limit the more widespread use of the alternative assay. This review will explore both the historical and more recent evidence for glomerular filtration estimation, including options to directly measure glomerular filtration (rather than estimate), perhaps the holy grail for both Biochemistry and Nephrology.

Role of Cystatin C in Predicting Disease Activity and Flare-Up in Systemic Lupus Erythematosus: A Longitudinal Follow-Up Study

Background:

We aimed to determine the sensitivity of serum cystatin C (Cys-C) in predicting lupus flare-up.

Methods:

In a longitudinal study, 77 patients were followed-up for up to 15 months. Cys-C, physician global assessment (PGA), and lupus activity index (SLEDAI) were recorded during each visit. Flare-up was defined as an increase ≥4 scores in SLEDAI compared to the last visit. The predictability of flare-up by Cys-C was evaluated by generalized linear-mixed effect model (GLMM) and generalized estimating equation (GEE). Predictive power of Cys-C, SLEDAI, and PGA was compared by the area under the curves (AUC) and application of receiver operating characteristic (ROC) curves.

Results:

Lupus flare-up was observed in 14 out of 77 patients on the 1^st visit, 3 out of 41 patients on the 2^nd visit, 2 out of 26 patients on the 3^rd visit, 1 out of 14 patients on the 4^th visit, and 1 out of 3 patients on the 5^th visit. Mean Cys-C levels in patients with flare-up vs. those with no flare-up in the 1^st, 2^nd, and 3^rd visits were 1769 vs. 1603 (P = 0.6), 5701 vs. 2117 (p = 0.2) and 1409 vs. 1731 (p = 0.9), respectively. Cys-C had lower predictive power than PGA and SLEDAI for either flare-up, active nephritis or SLEDAI in GLMM/GEE models. Cys-C also showed lower sensitivity (AUC = 0.701, 95%CI = 0.579-0.823, P = 0.003) than PGA and SLEDAI, to distinguish patients prone to flare-ups.

Conclusions:

Although Cys-C had some sensitivity for predicting flare-up, active nephritis or SLEDAI, its sensitivity was lower than that in PGA and SLEDAI.

Biomarkers of Drug-Induced Kidney Toxicity

Blood urea nitrogen and serum creatinine are imperfect markers of kidney function because they are influenced by many renal and nonrenal factors independent of kidney function. A biomarker that is released directly into the blood or urine by the kidney in response to injury may be a better early marker of drug-induced kidney toxicity than blood urea nitrogen and serum creatinine. Urine albumin and urine protein, as well as urinary markers kidney injury molecule-1 (KIM-1), β2-microglobulin (B2M), cystatin C, clusterin, and trefoil factor-3 (TFF-3) have been accepted by the Food and Drug Administration and European Medicines Agency as highly sensitive and specific urinary biomarkers to monitor drug-induced kidney injury in preclinical studies and on a case-by-case basis in clinical trials. Other biomarkers of drug-induced kidney toxicity that have been detected in the urine of rodents or patients include IL-18, neutrophil gelatinase-associated lipocalin, netrin-1, liver-type fatty acid-binding protein (L-FABP), urinary exosomes, and TIMP2 (insulin-like growth factor-binding protein 7)/IGFBP7 (insulin-like growth factor-binding protein 7), also known as NephroCheck, the first Food and Drug Administration-approved biomarker testing platform to detect acute kidney injury in patients. In the future, a combined use of functional and damage markers may advance the field of biomarkers of drug-induced kidney toxicity. Earlier detection of drug-induced kidney toxicity with a kidney-specific biomarker may result in the avoidance of nephrotoxic agents in clinical studies and may allow for earlier intervention to repair damaged kidneys.

Influence of age, gender, smoking, diabetes, thyroid and cardiac dysfunctions on cystatin C biomarker

BACKGROUND

Creatinine is the most widely used renal failure biomarker; however, it has a lot of drawbacks. One of the major drawbacks is the blind range (does not increase until 50% of the kidney deteriorates). On the other hand, cystatin C has gained more attention as a promising biomarker due to several advantages over creatinine. Cystatin C levels are elevated as soon as any mild defect in the kidney occurs. Furthermore, cystatin C is influenced by several non-renal diseases which provide an additional prognostic value for this promising biomarker.

OBJECTIVES

1. Study the effects of age, gender and smoking on cystatin C levels to. 2. Challenge the adoption of glomerular filtration rate equations for healthy population. 3. Compare the values generated from different glomerular filtration rate equations. 4. Evaluate the prognostic value of cystatin C for selected non-renal diseases.

METHODS

Using cross sectional analyses, we established the relationship between cystatin C levels and non-renal predictors. The quantification of cystatin C was performed by high performance liquid chromatographic method, while for creatinine by a colorimetric enzymatic method.

RESULTS

In the healthy volunteers the levels of cystatin C were slightly higher in men than in women and in individuals older than 50 years old than those under 50 years old and in smokers than non-smokers, however, statistical data confirmed a non-significant relationship with respect to the aforementioned factors. For the recruited patients suffering from (diabetes, hyper- and hypothyroidism and cardiac dysfunctions) a clear increase in cystatin C levels were observed with the exception of hypothyroidism patients in which a decrease in their cystatin C levels were observed.

CONCLUSION

Diabetes, thyroid and cardiac dysfunctions have a clear impact on the levels of cystatin C in human blood, whereas age, gender and smoking habit have no effect. Therefore, cystatin C could be considered as a useful biomarker of the aforementioned diseases, in turn, this requires extra precautions including the evaluation of several clinical conditions by physicians should CC is considered as a renal failure biomarker.

Serum creatinine and cystatin C provide conflicting evidence of acute kidney injury following acute ingestion of potassium permanganate and oxalic acid

AIM

Acute kidney injury (AKI) is common following deliberate self-poisoning with a combination washing powder containing oxalic acid (H₂C₂O₄) and potassium permanganate (KMnO₄). Early and rapid increases in serum creatinine (sCr) follow severe poisoning. We investigated the relationship of these increases with direct nephrotoxicity in an ongoing multicenter prospective cohort study in Sri Lanka exploring AKI following poisoning.

METHODS

Multiple measures of change in kidney function were evaluated in 48 consenting patients who had serial sCr and serum cystatin C (sCysC) data available.

RESULTS

Thirty-eight (38/48, 79%) patients developed AKI (AKIN criteria). Twenty-eight (58%) had AKIN stage 2 or 3. Initial increases in urine creatinine (uCr) excretion were followed by a substantial loss of renal function. The AKIN stage 2 and 3 (AKIN2/3) group had very rapid rises in sCr (a median of 118% at 24 h and by 400% at 72 h post ingestion). We excluded the possibility that the rapid rise resulted from the assay used or muscle damage. In contrast, the average sCysC increase was 65% by 72 h.

CONCLUSIONS

In most AKI, sCysC increases to the same extent but more rapidly than sCr, as sCysC has a shorter half-life. This suggests either a reduction in Cystatin C production or, conversely, that the rapid early rise of sCr results from increased production of creatine and creatinine to meet energy demands following severe oxidative stress mediated by H₂C₂O₄ and KMnO₄. Increased early creatinine excretion supports the latter explanation, since creatinine excretion usually decreases transiently in AKIN2/3 from other causes.

Mechanism-specific injury biomarkers predict nephrotoxicity early following glyphosate surfactant herbicide (GPSH) poisoning

Acute kidney injury (AKI) is common following glyphosate surfactant herbicide (GPSH) self-poisoning. Serum creatinine (sCr) is the most widely used renal biomarker for diagnosis of AKI although a recent study in rats suggested that urinary kidney injury molecule-1 predicted AKI earlier and better after GPSH-induced nephrotoxicity. We explored the utility of a panel of biomarkers to diagnose GPSH-induced nephrotoxicity in humans. In a prospective multi-centre observational study, serial urine and blood samples were collected until discharge and at follow-up. The diagnostic performance of each biomarker at various time points was assessed. AKI was diagnosed using the Acute Kidney Injury Network (AKIN) definitions. The added value of each biomarker to sCr to diagnose AKI was assessed by the integrated discrimination improvement (IDI) metric. Of 90 symptomatic patients, 51% developed AKI and 5 patients who developed AKIN≥2 died. Increased sCr at 8 and 16h predicted moderate to severe AKI and death. None of the 10 urinary biomarkers tested increased above normal range in patients who did not develop AKI or had mild AKI (AKIN1); most of these patients also had only minor clinical toxicity. Absolute concentrations of serum and urinary cystatin C, urinary interleukin-18 (IL-18), Cytochrome C (CytoC) and NGAL increased many fold within 8h in patients who developed AKIN≥2. Maximum 8 and 16h concentrations of these biomarkers showed an excellent diagnostic performance (AUC-ROC ≥0.8) to diagnose AKIN≥2. However, of these biomarkers only uCytoC added value to sCr to diagnose AKI when assessed by IDI metrics. GPSH-induced nephrotoxicity can be diagnosed within 24h by sCr. Increases in uCytoC and uIL-18 confirm GPSH-induces apoptosis and causes mitochondrial toxicity. Use of these biomarkers may help to identify mechanism specific targeted therapies for GPSH nephrotoxicity in clinical trials.

Role of biomarkers of nephrotoxic acute kidney injury in deliberate poisoning and envenomation in less developed countries

Acute kidney injury (AKI) has diverse causes and is associated with increased mortality and morbidity. In less developed countries (LDC), nephrotoxic AKI (ToxAKI) is common and mainly due to deliberate ingestion of nephrotoxic pesticides, toxic plants or to snake envenomation. ToxAKI shares some pathophysiological pathways with the much more intensively studied ischaemic AKI, but in contrast to ischaemic AKI, most victims are young, previously healthy adults. Diagnosis of AKI is currently based on a rise in serum creatinine. However this may delay diagnosis because of the kinetics of creatinine. Baseline creatinine values are also rarely available in LDC. Novel renal injury biomarkers offer a way forward because they usually increase more rapidly in AKI and are normally regarded as absent or very low in concentration, thereby reducing the need for a baseline estimate. This should increase sensitivity and speed of diagnosis. Specificity should also be increased for urine biomarkers since many originate from the renal tubular epithelium. Earlier diagnosis of ToxAKI should allow earlier initiation of appropriate therapy. However, translation of novel biomarkers of ToxAKI into clinical practice requires better understanding of non-renal factors in poisoning that alter biomarkers and the influence of dose of nephrotoxin on biomarker performance. Further issues are establishing LDC population-based normal ranges and assessing sampling and analytical parameters for low resource settings. The potential role of renal biomarkers in exploring ToxAKI aetiologies for chronic kidney disease of unknown origin (CKDu) is a high research priority in LDC. Therefore, developing more sensitive biomarkers for early diagnosis of nephrotoxicity is a critical step to making progress against AKI and CKDu in the developing world.

Mechanisms underlying early rapid increases in creatinine in paraquat poisoning

Background

Acute kidney injury (AKI) is common after severe paraquat poisoning and usually heralds a fatal outcome. The rapid large increases in serum creatinine (Cr) exceed that which can be explained by creatinine kinetics based on loss of glomerular filtration rate (GFR).

Methods and Findings

This prospective multi-centre study compared the kinetics of two surrogate markers of GFR, serum creatinine and serum cystatin C (CysC), following paraquat poisoning to understand and assess renal functional loss after paraquat poisoning. Sixty-six acute paraquat poisoning patients admitted to medical units of five hospitals were included. Relative changes in creatinine and CysC were monitored in serial blood and urine samples, and influences of non-renal factors were also studied.

Results

Forty-eight of 66 patients developed AKI (AKIN criteria), with 37 (56%) developing moderate to severe AKI (AKIN stage 2 or 3). The 37 patients showed rapid increases in creatinine of >100% within 24 hours, >200% within 48 hours and >300% by 72 hours and 17 of the 37 died. CysC concentration increased by 50% at 24 hours in the same 37 patients and then remained constant. The creatinine/CysC ratio increased 8 fold over 72 hours. There was a modest fall in urinary creatinine and serum/urine creatinine ratios and a moderate increase in urinary paraquat during first three days.

Conclusion

Loss of renal function contributes modestly to the large increases in creatinine following paraquat poisoning. The rapid rise in serum creatinine most probably represents increased production of creatine and creatinine to meet the energy demand following severe oxidative stress. Minor contributions include increased cyclisation of creatine to creatinine because of acidosis and competitive or non-competitive inhibition of creatinine secretion. Creatinine is not a good marker of renal functional loss after paraquat poisoning and renal injury should be evaluated using more specific biomarkers of renal injury.

Comparative assessment of neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C as early biomarkers for early detection of renal failure in patients with hypertension

BACKGROUND

Hypertension is one the most common causes of chronic kidney disease (CKD). One of the major concerns in hypertensive patients is early detection of renal disorders. In the past, serum creatinine (Scr) concentration was used as a marker of kidney function, but it proffers a late reflection of reduced glomerular filtration rate. Cystatin C and neutrophil gelatinase-associated lipocalin (NGAL) have been recently proven to be useful for quantification of CKD. Therefore, we compared the diagnostic value of NGAL with cystatin C and creatinine to evaluate kidney function in hypertensive patients.

METHODS

In this study, 42 hypertensive patients and 30 healthy volunteers were recruited. Serum cystatin C (Scys C) and plasma NGAL were measured using ELISA method. Creatinine, urea, hemoglobin, fibrinogen, and C-reactive protein were measured according to the routine methods. Estimated glomerular filtration rate (eGFR) was considered as the gold standard method (cut-off value of < 78 ml/min/1.73 m².

RESULTS

In the patient group, plasma NGAL, cystatin C, and creatinine were all significantly correlated with eGFR, and plasma NGAL correlated best with eGFR. Receiver-operating characteristics analysis indicated that plasma NGAL was a better indicator than creatinine and cystatin C for predicting a GFR < 78 ml/min/1.73 m2. The sensitivity and specificity for NGAL were 96% and 100%, for cystatin C were 92% and 60% and for creatinine were 76% and 47%, respectively.

CONCLUSION

Plasma NGAL demonstrated a higher diagnostic value to detect kidney impairment in the early stages of CKD as compared to Scys C and Scr in hypertensive patients.

[Usefulness of cystatin C as a prognostic marker in venous thromboembolism]

BACKGROUND AND OBJECTIVE

Cystatin C (cysC) is a prognostic marker in patients with hypertension, coronary heart disease and heart failure. The aim of this study was to determine the prognostic value of cysC levels obtained at the time of diagnosis in patients with venous thromboembolism (VTE).

MATERIAL AND METHOD

Retrospective study of a cohort of 226 consecutive patients with VTE, followed for 6 months. Serum samples were obtained for the determination of cysC, creatinine, and the N-terminal fraction of the brain natriuretic peptide (NT-proBNP) at the time of diagnosis.

RESULTS

The highest discriminating power value of dying at 6 months for cysC was 1,175mg/dl (sensitivity 76%, specificity 65%, positive predictive value 26%, negative predictive value 94%). Above the cut-off, 17/48 patients died, versus 9/152 that had lower levels (odds ratio: 5.98, 95% confidence interval [95% CI]: 2.50-14.29, P<.001). The adjusted hazard ratio in a multivariate model was 3.76 (95% CI 1.46-9.66). The accuracy of this parameter was similar to that for creatinine (1.24mg/dl) but lower than the NT-proBNP (435pg/ml). Patients who exceeded the limit values of cysC and NT-proBNP together had no greater risk of death than those above NT-proBNP only (odds ratio: 9.43, 95% CI 3.90-22.81, P<.001). There was no value, which was significantly associated with bleeding episodes or recurrent thromboembolism.

CONCLUSION

CysC concentration at the time of diagnosis in VTE patients has prognostic value, which is similar to that of serum creatinine and lower than that of NT-proBNP.

Association between kidney and cardiac diastolic function in Chinese subjects without overt disease: correlation with ageing and inflammatory markers

BACKGROUND

Age-related changes in kidney structure and function have been well documented. This study aimed to assess the relationship between declines of normal ageing-related kidney function and cardiac diastolic function in a healthy Chinese population.

MATERIALS AND METHODS

A total of 852 healthy adults aged 30-98 years were enrolled and divided into four groups according to quartiles of estimated glomerular filtration rate (eGFR) and cystatin C (CYSC). Cardiac diastolic function was measured by ratio of peak velocity of early filling to peak velocity of atrial filling (E/A), which was derived by B-mode echocardiography. Lower E/A was defined as measures under the 25th percentile of sample distribution (0·784).

RESULTS

Age was significantly associated with eGFR (r = -0·102, P < 0·01), CYSC (r = 0·544, P < 0·01) and E/A (r = -0·381, P < 0·01). Binary logistic regression analysis revealed that second, third and fourth quartile groups of CYSC and fourth quartile of eGFR were significantly associated with lower E/A in an unadjusted model. However, these associations were lost after full adjustment.

CONCLUSIONS

Our results confirm that ageing is a major factor contributing to declines in both kidney and cardiac diastolic function in a healthy population. Adjustment for covariates, however, showed that normal ageing-related declines in kidney function and cardiac diastolic function are not independently linked.

The impact of demographic characteristics and lifestyle in the distribution of cystatin C values in a healthy greek adult population

Background. The aim of the present study was to examine sources of variation for serum cystatin C in a healthy Greek population. Methods. Cystatin C together with basic clinical chemistry tests was measured in a total of 490 adults (46 ± 16 yrs, 40% males) who underwent an annual health check. Demographic, anthropometric, and lifestyle characteristics were recorded. Results. Higher values of cystatin C were observed among males (P = .04), participants aged over 65 years (P < .001), current smokers (P = .001) and overweight/obese participants (P = .03). On the contrary, alcohol consumption and physical activity seemed to have no influence on cystatin C levels (P = .61; P = .95, resp.). Conclusions. In interpreting serum cystatin C values in a healthy adult population, age, gender, Body Mass Index, and cigarette smoking need to be considered, and determination of reference ranges among distinct subpopulations seem to be prudent.

Gender does not influence cystatin C concentrations in healthy volunteers

BACKGROUND

Current data are conflicting about the influence of gender on cystatin C concentrations. The goal of this study was to determine the reference interval for serum cystatin C in normal Brazilian subjects, taking into account the influence of gender.

METHODS

Ninety-seven healthy volunteers, aged 18-70 years, 44% male, had glomerular filtration rate (GFR) measured using a (51)Cr-EDTA method and estimated with the Modification of Diet in Renal Disease (MDRD) study equation. Serum cystatin C was measured using a turbidimetric method, and creatinine by the Jaffe method.

RESULTS

Mean serum cystatin C was not significantly different between males and females, 0.62 +/- 0.12 vs. 0.65 +/- 0.12 mg/L, respectively (p = 0.26). However, median serum creatinine was significantly higher in men [97 (80-115) vs. 80 (53-88) micromol/L; p = 0.0001]. There were also no significant differences between genders with respect to GFR measured using (51)Cr-EDTA (103 +/- 14 for males and 106 +/- 19 mL/min/1.73 m(2) for females, p = 0.47), and estimated with the MDRD equation (86 +/- 12 vs. 83 +/- 16 mL/min/1.73 m(2), respectively, p = 0.24).

CONCLUSIONS

There was no effect of gender on serum cystatin C, as well as on measured and estimated GFR.

Non-invasive estimation of glomerular filtration rate (GFR). The Lund model: Simultaneous use of cystatin C- and creatinine-based GFR-prediction equations, clinical data and an internal quality check

Knowledge of glomerular filtration rate (GFR) is required to detect and follow impairment of renal function, to allow correct dosage of drugs cleared by the kidneys, and for the use of nephrotoxic contrast media. Correct determination of GFR requires invasive techniques, which are expensive, slow and not risk-free. Therefore, GFR-prediction equations based solely upon cystatin C or creatinine and anthropometric data or upon cystatin C, creatinine and anthropometric data have been developed. The combined prediction equations display the best diagnostic performance, but in several easily identifiable clinical situations (e.g. abnormal muscle mass, treatment with large doses of glucocorticoids) prediction equations based upon either cystatin C or creatinine are better than the combined equations. In Lund, where cystatin C has been used as a GFR-marker in the clinical routine since 1994, a strategy based upon this knowledge has therefore been developed. This comprises simultaneous use of a cystatin C-based and a creatinine-based GFR-prediction equation. If the GFRs predicted agree, the mean value is used as a reliable GFR-estimate. If the GFRs predicted do not agree, clinical data is evaluated to identify reasons for not using one of the two prediction equations and the GFR predicted by the other one is used. If no reasons for the difference in predicted GFRs are found, an invasive gold standard determination of GFR is performed. If the GFRs predicted agree for a patient, the creatinine value is reliably connected to a specific GFR and can be used to follow changes in GFR of that patient.

Cystatin C: current position and future prospects

Cystatin C is a low-molecular-weight protein which has been proposed as a marker of renal function that could replace creatinine. Indeed, the concentration of cystatin C is mainly determined by glomerular filtration and is particularly of interest in clinical settings where the relationship between creatinine production and muscle mass impairs the clinical performance of creatinine. Since the last decade, numerous studies have evaluated its potential use in measuring renal function in various populations. More recently, other potential developments for its clinical use have emerged. This review summarises current knowledge about the physiology of cystatin C and about its use as a renal marker, either alone or in equations developed to estimate the glomerular filtration rate. This paper also reviews recent data about the other applications of cystatin C, particularly in cardiology, oncology and clinical pharmacology.

Long-term creatine supplementation is safe in aged patients with Parkinson disease

The food supplement creatine (Cr) is widely used by athletes as a natural ergogenic compound. It has also been increasingly tested in neurodegenerative diseases as a potential neuroprotective agent. Weight gain is the most common side effect of Cr, but sporadic reports about the impairment of renal function cause the most concerns with regard to its long-term use. Data from randomized controlled trials on renal function in Cr-supplemented patients are scarce and apply mainly to healthy young athletes. We systematically evaluated potential side effects of Cr with a special focus on renal function in aged patients with Parkinson disease as well as its current use in clinical medical research. Sixty patients with Parkinson disease received either oral Cr (n = 40) or placebo (n = 20) with a dose of 4 g/d for a period of 2 years. Possible side effects as indicated by a broad range of laboratory blood and urine tests were evaluated during 6 follow-up study visits. Overall, Cr was well tolerated. Main side effects were gastrointestinal complaints. Although serum creatinine levels increased in Cr patients because of the degradation of Cr, all other markers of tubular or glomerular renal function, especially cystatin C, remained normal, indicating unaltered kidney function. The data in this trial provide a thorough analysis and give a detailed overview about the safety profile of Cr in older age patients.

Biomarkers of acute kidney injury

The diagnosis of acute kidney injury (AKI) is usually based on measurements of blood urea nitrogen (BUN) and serum creatinine. BUN and serum creatinine are not very sensitive or specific for the diagnosis of AKI because they are affected by many renal and nonrenal factors that are independent of kidney injury or kidney function. Biomarkers of AKI that are made predominantly by the injured kidney have been discovered in preclinical studies. In clinical studies of patients with AKI, some of these biomarkers (eg, interleukin-18, neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1) have been shown to increase in the urine before the increase in serum creatinine. These early biomarkers of AKI are being tested in different types of AKI and in larger clinical studies. Biomarkers of AKI may also predict long-term kidney outcomes and mortality.

Serum Cystatin C in Estimating Glomerular Filtration Rate

Using serum cystatin C in estimating glomerular filtration rate (GFR) has in recent times been recommended. A number of simple formulas for calculating GFR have been derived specifically from serum cystatin C concentrations. The purpose of this study was to assess the significance of cystatin C and of the two most frequently applied of these formulas in estimating glomerular filtration rate compared to serum creatinine and its derived formulas for estimating glomerular filtration rate from creatinine concentrations. The study included 74 patients: 59 were in various stages of chronic renal insufficiency (divided into two subgroups: I with GFR ≥ 60 mL/min/1.73m2and II with GFR<60 mL/min/1.73m2) and 15 on hemodialysis. A control group of 30 healthy participants was also included in the study. Serum values of cystatin C ranged from: 0.86 ± 0.16 mg/L in subgroup I, and 1.77 ± 0.79 mg/L in subgroup II, to 6.9 ± 1.83 mg/L in patients on hemodialysis. The correlation between the two formulas derived from cystatin C and the clearance of creatinine, as well as the Cockcroft and Gault's formula, was significant, while one of the formulas derived from cystatin C did not show a significant correlation with MDRD. It was concluded that serum cystatin C is a significant marker in estimating glomerular filtration rate, especially in the advanced stages of chronic renal insufficiency.

Genotype and plasma concentration of cystatin C in patients with late-onset Alzheimer disease

BACKGROUND

A polymorphism locating at position 73 of cystatin C (CST3) exon 1 was suggested to be associated with Alzheimer disease (AD), but with contradictory results. The relationship between the CST3 genotype and the cystatin C plasma level in AD remains unknown.

OBJECTIVE

We aim to determine the association between CST3 polymorphism and the plasma levels of cystatin C in AD and nondemented control individuals.

METHOD

The polymorphisms of the CST3 genotype were determined using PCR followed by restriction fragment length polymorphism analysis, and the plasma cystatin C concentrations were quantified by sandwich ELISA in 175 AD and 461 control subjects.

RESULTS

Although the CST3A allele frequencies were similar between the two groups, the CST3A/A homozygote was significantly associated with late-onset AD. As expected, the established AD genetic risk factor APOE epsilon4 allele was overrepresented in the AD cohort. The plasma cystatin C levels were lower in the AD patients than in the control group. Furthermore, plasma cystatin C levels were associated positively with age and negatively with CST3A allele in the control group.

CONCLUSION

The homozygous CST3A/A genotype confers a risk for AD in Taiwan Chinese. Such an association may be due to the reduced level of cystatin C in the peripheral circulation.

Serum cystatin C as a better marker of vancomycin clearance than serum creatinine in elderly patients

OBJECTIVES

The purpose of this study is to assess the usefulness of the concentration of cystatin C (Cys-C) in serum for predicting the clearance of vancomycin (CLvcm) compared with the serum concentration of creatinine (SCr) in the elderly.

METHODS

Thirty-nine serum samples were obtained from 24 elderly patients (65 years and older). Creatinine clearance (CLcr) and the glomerular filtration rate calculated from the concentration of Cys-C (GFRcys-c) were estimated using Cockcroft & Gault's formula and Larsson's formula, respectively.

RESULTS

The correlation constant for CLvcm and the reciprocal of Cys-C (p=0.883) was significantly higher than that for CLvcm and the reciprocal of SCr (p=0.575, p<0.005). GFRcys-c was strongly correlated with CLvcm (p=0.883) and the constant was significantly higher than that for the correlation between CLvcm and CLcr (p=0.684, p<0.05). These results suggest that the serum concentration of Cys-C is a more reliable marker for predicting CLvcm than is SCr in elderly patients.

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

OBJECTIVES

To perform a systematic review comparing the diagnostic accuracy of CysC with SCr.

METHODS

MEDLINE and EMBASE (January 1984-February 2006) were searched. Studies included i) evaluated CysC against a recognised 'gold standard' method for determining GFR using a receiver operating characteristics (ROC) curve analysis and ii) included data that could be extracted into a 2x2 table.

RESULTS

The search identified 27 population groups in 24 studies (n=2007) that compared the diagnostic accuracy of CysC with SCr. The diagnostic odds ratios (DORs) (95% CI) of predicting renal dysfunction derived from a Moses-Littenberg linear regression model were 3.99 (3.41-4.57) for CysC and 2.79 (2.12-3.46) for SCr.

CONCLUSION

The diagnostic accuracy for impaired renal function favours CysC. However, the confidence intervals for the pooled DORs for the biomarkers overlap. The ability of CysC (cut-off values between 0.9 and 1.4 mg/L) to rule in renal impairment (as measured by inulin-determined GFR of 60-79 mL/min/1.73 m2) in persons in whom this is suspected is large and conclusive.

Cystatin C as a reliable marker of renal function following heart valve replacement surgery with cardiopulmonary bypass

BACKGROUND

Little is known about serum cystatin C as a marker of renal function in cardiac surgery patients. The aim of this study was to assess its utility post cardiopulmonary bypass (CPB).

METHODS

60 heart valve replacement patients were enrolled, and 26 of them had low-dose corticosteroid treatment on the first 3 days postoperatively. Serum creatinine, serum cystatin C and 24-h creatinine clearance rate (CCR) adjusted by body surface area were determined preoperation, days 1, 2, 3, 7 post operation.

RESULTS

Serum creatinine increased and peaked at day 3 postoperatively, while cystatin C peaked at day 2, and the adjusted CCR also reached a minimum at day 2. The inverse of cystatin C correlated better with CCR than that of creatinine (r=0.751 vs. 0.629). Using adjusted CCR as "golden standard", cystatin C was superior to creatinine in diagnosing renal dysfunction (area under the curve [AUC] for cystatin C 0.876, 95% confidence interval 81.8-93.4; AUC for creatinine 0.801, 95% confidence interval 72.5-87.7; p=0.045). Low-dose corticosteroid treatment has no significant effect on cystatin C.

CONCLUSION

In agreement with many other investigators, the present findings support cystatin C is a reliable marker of renal function. It is superior to creatinine in patients post CPB.

Post-conditioning by a short administration of desflurane reduced renal reperfusion injury after differing of ischaemia times in rats

BACKGROUND

'Anaesthetic post-conditioning', that is administration of anaesthetics during early reperfusion, is known to have positive effects on several organs. For the kidney, however, the effects of post-conditioning by volatile anaesthetics are not well researched. We examined renal function and morphology after post-conditioning by desflurane.

METHODS

Anaesthetized rats were subjected to 30 or 45 min of renal ischaemia 14 days after contralateral nephrectomy. Post-conditioning was achieved by administration of 1 MAC desflurane (6.7 vol%) for 15 min during early reperfusion (all groups n=8). Cystatin C (CyC), creatinine clearance (Cl(Cr)) and fractional sodium excretion (FE(Na)) were measured in the awake rats over 3 days. Cell damage was graded from 1 to 4 in histological sections. Functional variables [mean (SD)] were compared statistically by a one-way anova followed by Bonferroni's multiple comparison test and histological scores (median and range) by Kruskal-Wallis test followed by Dunn's multiple comparison test.

RESULTS

Pre-ischaemia function did not differ between the groups, but was markedly reduced after ischaemia. After 30 min ischaemia, the area under the curve (AUC) for Cl(Cr) was smaller in the desflurane than in the control group [21.5 (5.0) vs 31.6 (5.1) ml min(-1) h, P<0.05]. After 45 min desflurane reduced the AUC compared with the control group for both CyC [15 (4) vs 21 (3) mg litre(-1) h] and FE(Na) [1054 (221) vs 1570 (572)% h, both P<0.05). Morphological differences were greater between the 30 min groups [control: 2.75 (2.0-3.5) vs desflurane: 1.5 (1.0-2.5); P<0.05] than between the 45 min groups [control: 3.5 (3.0-4.0) vs desflurane: 3.0 (1.5-4.0)].

CONCLUSION

Desflurane post-conditioning protects renal function and tissue. This protection was greater after the short episode than after the long episode of ischaemia.

Cystatin C reference values and aging

OBJECTIVES

The aim of this study was to determine the reference values for serum cystatin C (CysC) with a particular focus on the effect of aging.

DESIGN AND METHODS

The study was performed on a consecutive series of subjects (258 men and 396 women). Laboratory parameters and a detailed personal and family medical history were collected.

RESULTS

CysC showed a significant correlation with age in both sexes, which was confirmed with multivariate linear regression after adjustment for SCr (serum creatinine). Age-related reference intervals were established for cystatin C (<45 years, <0.95 mg/L and >45 years, <1.20 mg/L).

CONCLUSIONS

The use of CysC reference values adjusted for age should be carefully taken into consideration.