Reference intervals for serum cystatin C and serum creatinine in adults

Comparison of Creatinine and Cystatin C to Estimate Renal Function in Geriatric and Frail Patients

The aim of this study was to compare estimated glomerular filtration rate (eGFR) with creatinine (eGFRcrea) and cystatin C (eGFRcys) in geriatric and frail patients. A retrospective, cross-sectional study was performed at a geriatric clinic in Stockholm (n = 95). The revised Lund−Malmö equation was used to calculate eGFRcrea and the Caucasian-Asian-Pediatric-Adult (CAPA) equation was used for eGFRcys. The absolute mean percentage difference between eGFRcrea and eGFRcys was used as a surrogate measure for accuracy in eGFR. Other outcome measures were consistency expressed in Lin’s concordance correlation coefficient and the proportion of consistent staging of renal failure. Subgroup analyses were performed with regard to frailty (according to Clinical Frailty Scale) and age. eGFRcys estimated lower GFR than eGFRcrea across the entire study population as well as in all subgroups (p < 0.05). Difference between the estimates increased with increasing frailty (r2 = 0.15, p < 0.01), but was not significantly affected by age (r2 = 0.004, p = 0.55). In conclusion, eGFRcys was significantly lower compared to eGFRcrea in geriatric and frail patients. Moreover, frailty had greater impact than age on the accuracy of eGFR. However, this study cannot determine if any of the estimates are preferable over the other in this patient group.

Reference intervals for serum cystatin C and serum creatinine in an adult sub-Saharan African population

Background

Serum cystatin C (SCysC) and serum creatinine (SCr) are two biomarkers used in common practice to estimate the glomerular filtration rate (GFR). For SCysC and SCr to be used in a given population, normal values need to be determined to better assess patients. This study aimed to determine SCysC and SCr reference intervals (RIs) in a Cameroonian adult population and factors susceptible of influencing them.

Methods

We carried-out a cross-sectional study from November 2016 to May 2017 in Yaoundé, Cameroon. Participants were Cameroonians aged 18 years and above, residing inside the country and found in good health at study inclusion. SCysC and SCr were determined by particle-enhanced turbidimetric immunoassay standardized against the ERM-DA471/IFCC reference material and by the IDMS reference modified Jaffe kinetic method, respectively. RIs were determined using the 2.5th and 97.5th percentiles and their respective 90% confidence intervals (CIs). The quantile regression served to identify potential factors likely influencing SCysC and SCr values.

Results

We included 381 subjects comprising 49.1% females.. RIs for SCysC varied between 0.57 (90%CI: 0.50–0.60) and 1.03 mg/L (90%CI: 1.00–1.10) for females, and from 0.70 (90%CI: 0.60–0.70) to 1.10 mg/L (90%CI: 1.10–1.20) for males. Concerning SCr, its RIs ranged from 0.58 (90%CI: 0.54–0.61) to 1.08 mg/dL (90%CI: 1.02–1.21) for females, and from 0.74 (90%CI: 0.70–0.80) to 1.36 mg/dL (90%CI: 1.30–1.45) for males. Men had significantly higher SCysC and SCr values than women (p <  0.001). Likewise, subjects aged 50 years and above had higher SCysC values in comparison to younger age groups (p <  0.001), which was not the case for SCr values (p = 0.491). Moreover, there was a positive and significant correlation between SCysC and SCr in women (ρ = 0.55, p < 0.001), in men (ρ = 0.39, p < 0.001) and globally (ρ = 0.58; p < 0.001). Furthermore, the sex influenced both biomarkers’ values across all quantile regression models while age and body surface area (BSA) influenced them inconsistently.

Conclusion

This study has determined serum cystatin C and serum creatinine reference intervals in an adult Cameroonian population, whose interpretations might take into account the patient’s sex and to a certain extent, his/her age and/or BSA.

Electronic supplementary material

The online version of this article (10.1186/s12907-019-0086-7) contains supplementary material, which is available to authorized users.

Serum cystatin C as an indicator for early detection of diabetic nephropathy in type 2 diabetes mellitus

BACKGROUND

Diabetes mellitus (DM) refers to a group of common metabolic disorders that share the phenotype of hyperglycemia. The metabolic dysregulations associated with DM causes secondary pathophysiological changes in multiple organ systems which result in various complications, responsible for the morbidity and mortality associated with the disease.

METHODS

The present study was carried out on 40 patients with type 2 diabetes mellitus, who were recruited from those attending outpatient clinic and inpatient of Internal Medicine Department at The National Institute of Diabetes and Endocrinology from January 2017 to june 2017.

RESULTS

The mean Cystatin C values in Group I were 0.74, group II were 1.07. and in Group III were 3.25, The results show that the Cystatin C values were raised even in the patients with Normoalbuminuria with GFR ≥90 whom clinical albuminuria had not yet started.

CONCLUSIONS

serum Cystatin C may be considered as an early marker, than microalbuminuria and serum creatinine, the commonly used marker for nephropathy, for declining renal function, in diabetic subjects. Further studies in larger population are needed to confirm this result.

Reference intervals for plasma cystatin C and plasma creatinine in adults using methods traceable to international calibrators and reference methods

INTRODUCTION

The aim of this study was to establish reference intervals for plasma cystatin C and creatinine in adults using the Gentians cystatin C method traceable to the international calibrator standard ERM-DA471/IFCC and a creatinine method traceable to the IDMS (Isotope Dilution Mass Spectrometry) creatinine reference method.

METHODS

Blood samples were collected from 304 healthy blood donors (152 men and 152 women between 17 and 66 years old) with 30-31 men and 30-31 women in each ten-year interval. Plasma cystatin C was analyzed using the Gentian Cystatin C assay on a Roche cobas c702 analyzer, and plasma creatinine was analyzed using the CREA Plus assay on the Roche Modular P analyzer.

RESULTS

The nonparametric reference intervals for plasma cystatin C were 0.58-1.00 mg/L in women (median 0.78 mg/L, range 0.56-1.06 mg/L) and 0.62-1.04 mg/L in men (median 0.79 mg/L, range 0.61-1.07 mg/L). The Mann-Whitney U test revealed no gender-related difference in plasma cystatin C (P = .21). A common reference interval in women and men was calculated to be 0.61-1.01 mg/L (median 0.79 mg/L, range 0.56-1.07 mg/L). The nonparametric reference interval for plasma creatinine was 52-89 μmol/L in women (median 69 μmol/L, range 52-92 μmol/L) and 61-108 μmol/L in men (median 86 μmol/L, range 56-118 μmol/L). The Mann-Whitney U test revealed a gender-related difference in plasma creatinine (P < .0001).

CONCLUSION

In conclusion, we have established reference intervals for plasma cystatin C and creatinine in adults using methods traceable to international standards.

Adult Reference Ranges for Serum Cystatin C, Creatinine and Predicted Creatinine Clearance

Serum cystatin C measurement has been previously shown by ourselves and others to be a better indicator of changes in glomerular filtration rate (GFR) than serum creatinine. However, the available literature on reference values for cystatin C concentration remains surprisingly sparse; we thus set out to determine an adult reference range. Blood was taken from 309 healthy blood donors and creatinine and cystatin C concentrations were measured using commercially available automated methodologies. In addition, predicted creatinine clearances were calculated using the Cockcroft and Gault formula. The 95% reference intervals for creatinine, predicted creatinine clearance and cystatin C for all blood donors, regardless of gender, were 68–118 μmol/L, 58–120 ml/min/1·73 m2 and 0·51–0·98 mg/L, respectively. For women, the intervals were 68–98 μmol/L, 60–119 ml/min/1·73 m2 and 0·49–0·94 mg/L; for men, they were 78–123 μmol/L, 57–122 ml/min/1·73 m2 and 0·56–0·98 mg/L. The mean 95% reference interval for cystatin C in all donors under 50 years of age was 0·53–0·92 mg/L; for those over 50 years of age it was 0·58–1·02 mg/L. The small difference between male and female ranges meant that a single reference range for cystatin C could be established for all adults under 50 years of age without adjustment for body surface area. Serum cystatin C measurement offers a simpler and more sensitive screening test than serum creatinine for early changes in GFR.

A validated LC–MS/MS method for the quantitative measurement of creatinine as an endogenous biomarker in human plasma

Background: Creatinine is an endogenous compound generated from creatine by normal muscular metabolism. It is an important indicator of renal function and the serum level is routinely monitored in clinical labs. Results & methodology: Surrogate analyte (d3-creatinine) was used for calibration standard and quality control preparation and the relative instrument response ratio between creatinine and d3-creatinine was used to calculate the endogenous creatinine concentrations. Conclusion: A fit-for-purpose strategy of using a surrogate analyte and authentic matrix was adopted for this validation. The assay was the first human plasma assay using such strategy and was successfully applied to a clinical study to confirm a transient elevation of creatinine observed using an existing clinical assay.

Biomarkers in cardiorenal syndromes

Cardiac and renal diseases often coexist and patients with cardiac and renal failure have high morbidity and mortality. Cardiorenal syndromes (CRSs) are disorders of the heart and kidneys whereby dysfunction in one organ may induce dysfunction in the other organ. Five subtypes of CRSs have been defined by the Acute Dialysis Quality Initiative Consensus Group. There is a need for early detection and monitoring of patients with CRSs. Biomarkers play a key role in the diagnosis and monitoring of acute myocardial infarction, chronic heart failure, and chronic kidney disease. In recent years, new biomarkers have been identified that may play a role in the early diagnosis of acute kidney injury. Herein, we review the use of serum and urine biomarkers in the diagnosis and management of CRSs. The established cardiac and renal biomarkers such as the cardiac troponins, natriuretic peptides, urine albumin, and creatinine, as well as the new renal biomarkers cystatin C and neutrophil gelatinase-associated lipocalin are reviewed in detail. The recent advances in assay methods, clinical studies, and recommendations in clinical guidelines are discussed. With advances in biomarker research, in future, perhaps a multimarker approach will become feasible to stratify the diagnosis of CRS for individualized treatment and prognosis.

Cystatin C: a new renal marker and its potential use in small animal medicine

The occurrence of chronic kidney disease is underestimated in both human and veterinary medicine. Glomerular filtration rate (GFR) is considered the gold standard for evaluating kidney function. However, GFR assessment is time-consuming and labor-intensive and therefore not routinely used in practice. The commonly used indirect GFR markers, serum creatinine (sCr) and urea, are not sufficiently sensitive or specific to detect early renal dysfunction. Serum cystatin C (sCysC), a proteinase inhibitor, has most of the properties required for an endogenous GFR marker. In human medicine, numerous studies have evaluated its potential use as a GFR marker in several populations. In veterinary medicine, this marker is gaining interest. The measurement is easy, which makes it an interesting parameter for clinical use. This review summarizes current knowledge about cystatin C (CysC) in humans, dogs, and cats, including its history, assays, relationship with GFR, and biological and clinical variations in both human and veterinary medicine.

Delineation of concentration ranges and longitudinal changes of human plasma protein variants

Human protein diversity arises as a result of alternative splicing, single nucleotide polymorphisms (SNPs) and posttranslational modifications. Because of these processes, each protein can exists as multiple variants in vivo. Tailored strategies are needed to study these protein variants and understand their role in health and disease. In this work we utilized quantitative mass spectrometric immunoassays to determine the protein variants concentration of beta-2-microglobulin, cystatin C, retinol binding protein, and transthyretin, in a population of 500 healthy individuals. Additionally, we determined the longitudinal concentration changes for the protein variants from four individuals over a 6 month period. Along with the native forms of the four proteins, 13 posttranslationally modified variants and 7 SNP-derived variants were detected and their concentration determined. Correlations of the variants concentration with geographical origin, gender, and age of the individuals were also examined. This work represents an important step toward building a catalog of protein variants concentrations and examining their longitudinal changes.

Reference intervals of several renal and hepatic function parameters for apparently healthy adults from Eastern China

BACKGROUND

Biochemical substances relating to renal and hepatic function are influenced not only by individual factors such as gender, lifestyle, and age but also by ecological factors, such as altitude, climate, and ethnic background. The purpose of the present study was to establish reference intervals for 16 biochemical substances relating to renal and hepatic function in healthy Chinese adults.

METHODS

A total of 2,405 apparently healthy individuals (18-77 years of age) were chosen as reference individuals in the present study. The 16 biochemical substances relating to renal and hepatic function were analyzed using a HITACHI RL7600 analyzer. The reference intervals were established using nonparametric methods to estimate the 2.5 and 97.5 percentiles of the distribution as the lower and the upper limits, respectively.

RESULTS

Age- and gender-appropriate reference intervals were established for some biochemical substances relating to renal and hepatic function in healthy Chinese adults.

CONCLUSION

The reference intervals established in this study can provide a useful clinical tool for the assessment of the kidney and liver damage. In addition, the established reference intervals can be adopted in other clinical laboratories after further validation.

Reference intervals and factors contributing to serum cystatin C levels in a Chinese population

BACKGROUND

Serum cystatin C (Cys-C), an inhibitor of cysteine proteases, has been suggested as an ideal biomarker of glomerular filtration rate (GFR).

OBJECTIVES

The objective of this study was to describe the reference intervals of serum Cys-C and identify factors associated with serum Cys-C or its variability, including age, gender, creatinine (Crea), blood urea nitrogen (BUN), and uric acid (UA).

DESIGN AND METHODS

Serum Cys-C, Crea, BUN, and UA were measured in 4,517 healthy participants aged 8-89 years attending our hospital. Serum Cys-C was analyzed using a latex-enhanced immunoturbidimetric method. Crea were tested by picric acid jaffe method, BUN, and UA by kinetic UV assays.

RESULTS

The predominant characteristic of Cys-C distribution was that Cys-C concentration in age ≥60 years group was the highest (P < 0.05). The differences of Cys-C concentration between males and females existed for subjects aged from 30 to 59 years (P < 0.05). In a multiple model adjusted only for gender and age, gender (β = 0.007) has stronger effect on Cys-C levels, compared with age (β = 0.003). The clinical variables, comprised of age, gender, Crea, BUN, and UA, involved in the fully adjusted equation accounted for 37.6% of variation of Cys-C.

CONCLUSIONS

Ninety-five percent reference intervals for healthy population were partitioned into three categories only by age, 0.59-1.07 mg/L for subjects aged 19-59 years; 0.74-1.14 mg/L for the older aged ≥60 years; and 0.63-1.11 mg/L for children aged ≤18 years. Serum Cys-C is significantly related to gender, age, UA, Crea, and BUN. Besides, there are still other factors contributing to variation of Cys-C levels.

Determination of cathepsin S abundance and activity in human plasma and implications for clinical investigation

There is strong experimental evidence associating cathepsin S with the pathogenesis of atherosclerosis, with emerging data to support its role in diseases such as abdominal aortic aneurysm, obesity, and type 2 diabetes. To further our understanding of cathepsin S, we have developed a novel sandwich immunoassay to measure the mature form of cathepsin S in plasma (mean values from 12 healthy donors of 53±17ng/ml, range=39-102). We also developed a targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay to measure in vitro cathepsin S activity to compare activity levels with the protein mass levels determined by enzyme-linked immunosorbent assay (ELISA). Interestingly, we observed that only 0.4 to 1.1% of circulating cathepsin S was enzymatically active. We subsequently demonstrated that the attenuated activity we observed resulted from binding between cathepsin S and its endogenous inhibitor cystatin C in plasma. These data were obtained through immunoprecipitation coupled with either Western blotting analysis or in-gel tryptic digestion and LC-MS/MS characterization of Coomassie-stained gel bands. Although many laboratories have explored the relationship between cathepsin S and cystatin C, this is the first study to demonstrate their association in human circulation, a finding that could prove to be important in furthering our understanding of cathepsin S biology.

Mass spectrometry-based protein assays for in vitro diagnostic testing

Mass spectrometry-based protein assays hold great promise for in vitro diagnostic testing. Technological advances in mass spectrometry have given rise to instruments and methods that are fully capable of automated and high-throughput protein assaying. Yet, the numerous steps involved in such assays can lead to difficulties in assay characterization and validation, and can also make them unnecessarily complex and prohibitively expensive for everyday use. Simplification of both approaches and instrumentation seems to be the solution to the fast introduction of the mass spectrometry-based assays into the clinical laboratories. One such simplified approach is the mass spectrometric immunoassay, which couples targeted immunoaffinity protein separation with the power of mass spectrometry detection. Several mass spectrometric immunoassays have been extensively characterized and have found their way into clinical laboratory improvement amendments-certified laboratories in the form of laboratory developed tests. Reviewed in this special report is the development and validation of one of those assays - a Cystatin mass spectrometric immunoassay. With the added advantage of protein variant detection and quantification, these assays can redefine our view of protein diversity, with clear implications in biomarker discovery, validation, and ultimately, in vitro diagnostic testing.

Serum Beta 2-microglobulin/cystatin C index: a useful biomarker in lupus nephritis?

BACKGROUND

Systemic lupus erythematosus (SLE) is a chronic multisystem autoimmune disease with frequent flares. Our aim was to evaluate the beta 2-microglobulin/cystatin C (β2M/CysC) index versus other markers as a predictor factor for assessment of SLE reactivation.

METHODS

We prospectively analyzed 42 patients with lupus nephritis. Disease activity was classified using SLEDAI-2K and BILAG. Routine renal function and laboratory markers of SLE activity were performed, as well as serum β2M (Sβ2M)/serum CysC (SCysC) and Sβ2M/serum creatinine (SCreat) indexes determinations.

RESULTS

The 42 enrolled patients had a mean age of 37.7 ± 13.1 years, 88% were female and 67% Caucasians; mean estimated glomerular filtration rate was 61.9 ± 20.0 ml/min/1.73 m(2). There was a strong correlation between SCreat versus SCysC (r = 0.887), SCreat versus Sβ2M (r = 0.865), and SCysC versus Sβ2M (r = 0.880). Multivariate analysis showed that the Sβ2M/SCreat index is a prognostic factor predicting active lupus nephritis.

CONCLUSION

As SCysC is a good marker of renal function, it would be expected that the Sβ2M/SCysC index could be a better indicator of renal activity than Sβ2M/SCreat, but in the present study it did not add relevant clinical information in the assessment of renal activity in SLE.

Cystatin C as a marker of glomerular filtration rate in voluntary kidney donors

OBJECTIVES

Cystatin C is emerging as an endogenous marker of glomerular filtration rate. This study sought to assess the usefulness of serum cystatin C as a marker of glomerular filtration rate in comparison with serum creatinine and serum creatinine-based glomerular filtration rate estimations in voluntary kidney donors.

MATERIALS AND METHODS

Serum cystatin C and serum creatinine were estimated in 35 voluntary kidney donors. Glomerular filtration rate was estimated using: (1) Cockcroft-Gault method normalized to 1.73 m(2) of body surface area, (2) 4-variable Modification of Diet in Renal Diseases formula, and (3) (99m)Tc-DTPA double plasma sampling method. Glomerular filtration rate-double plasma sampling method was used as a reference value. Results were expressed as means ± SD.

RESULTS

The mean age of the participants was 44.23 ± 8.61 years old (19 women, 16 men). The mean serum creatinine was 0.83 ± 0.14 mg/dL, and the mean serum cystatin C was 0.71 ± 0.12 mg/L. Serum cystatin C showed significant correlation with serum creatinine (r = 0.864; P < .001). Glomerular filtration rate-MDRD showed the strongest correlation with glomerular filtration rate double plasma sampling method (r = 0.93; P < .001), followed by glomerular filtration rate-Cockcroft-Gault (r = 0.76; P < .001 ), serum creatinine (r = - 0.68; P < .001), and serum cystatin C (r = - 0.59; P < .001). The mean serum cystatin C values were 22.6% higher in men than in women. There was a significant correlation of serum cystatin C with glomerular filtration rate-Cockcroft-Gault (r = - 0.50; P = .002 ), glomerular filtration rate-MDRD (r = - 0.59; P < .001 ), and glomerular filtration rate-double plasma sampling method (r = - 0.59; P < .001 ).

CONCLUSIONS

Serum cystatin C is an optimal marker of glomerular filtration rate in voluntary kidney donors.

Interpreting different measures of glomerular filtration rate in obesity and weight loss: pitfalls for the clinician

To combat the increasing incidence of obesity, much research has been devoted to devising successful strategies for weight loss, including manipulation of diet and gastric surgery. Obesity itself can be associated with renal dysfunction, and the degree of reversibility of this with weight loss has being studied. However, there are significant limitations and flaws in the methods we have available to measure glomerular filtration rate (GFR) in overweight and obese subjects. Obesity is associated with changes in body composition including lean and fat mass. This has implications for assumptions that underpin creatinine-based measures such as creatinine clearance, estimated GFR and other equations devised for obesity including the Salazar-Corcoran equation. These changes in body composition also affect measures of glomerular filtration such as cystatin C and nuclear medicine isotope scans. This article will review the accuracy of these current measures of renal function in the obese and consider the evidence for adjusting for body surface area or adjusting for lean body mass. Finally, the effect of weight loss itself on serial measurements of renal function in a given individual, independent of a true change in renal function, will be reviewed. Ultimately using the Cockcroft-Gault equation with an adjustment for lean body mass seems to be the best measure for renal function in obesity. No method for measuring renal function in situations of weight loss has been shown to be unequivocally superior.

Targeted quantitative mass spectrometric immunoassay for human protein variants

BACKGROUND

Post-translational modifications and genetic variations give rise to protein variants that significantly increase the complexity of the human proteome. Modified proteins also play an important role in biological processes. While sandwich immunoassays are routinely used to determine protein concentrations, they are oblivious to protein variants that may serve as biomarkers with better sensitivity and specificity than their wild-type proteins. Mass spectrometry, coupled to immunoaffinity separations, can provide an efficient mean for simultaneous detection and quantification of protein variants.

RESULTS

Presented here is a mass spectrometric immunoassay method for targeted quantitative proteomics analysis of protein modifications. Cystatin C, a cysteine proteinase inhibitor and a potential marker for several pathological processes, was used as a target analyte. An internal reference standard was incorporated into the assay, serving as a normalization point for cystatin C quantification. The precision, linearity, and recovery characteristics of the assay were established. The new assay was also benchmarked against existing cystatin C ELISA. In application, the assay was utilized to determine the individual concentration of several cystatin C variants across a cohort of samples, demonstrating the ability to fully quantify individual forms of post-translationally modified proteins.

CONCLUSIONS

The mass spectrometric immunoassays can find use in quantifying specific protein modifications, either as a part of a specific protein biomarker discovery/rediscovery effort to delineate the role of these variants in the onset of the disease, progression, and response to therapy, or in a more systematic study to delineate and understand human protein diversity.

Changes in dietary protein intake has no effect on serum cystatin C levels independent of the glomerular filtration rate

Cystatin C is being considered as a replacement for serum creatinine in the estimation of the glomerular filtration rate (GFR); however, its plasma levels might be affected by factors other than the GFR, such as protein intake. We performed a post hoc analysis of the data in the Modification of Diet in Renal Disease study, in which we compared serum creatinine and cystatin C levels in 741 patients with available estimates of protein intake at baseline prior to their randomization to diets containing various amounts of protein, and at 2 years of follow-up in 426 of these patients in whom a cystatin C measurement was available. The 503 patients in study A (GFR 25-55 ml/min per 1.73 m(2)) had been assigned a low (0.58 g/kg per day) or a usual (1.3 g/kg per day) protein intake, and the 238 participants in study B (GFR 13-24 ml/min per 1.73 m(2)) were assigned a very low (0.28 g/kg per day) or the low protein intake. In either study group, lowering the dietary protein intake reduced the change in creatinine, but did not have a significant change in cystatin C. Thus, in patients with moderate-to-severe chronic kidney disease, serum cystatin C unlike serum creatinine was not affected by dietary protein intake independent of changes in GFR. Hence, cystatin C may allow more accurate estimates of GFR than creatinine for patients with reduced protein intake. Further study of other non-GFR determinants of cystatin C is needed before the widespread adoption.

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.

Biological variation of cystatin C and creatinine

OBJECTIVE

To evaluate the day-to-day biological variation of cystatin C in comparison with creatinine in healthy subjects and in patients with impaired renal function.

MATERIAL AND METHODS

Eight weekly morning blood samples were taken from 20 healthy subjects (13 females and 7 males, median age 44 years, range 25-61) and 19 patients with impaired renal function (8 females and 11 males, median age 61 years, range 35-70). Serum cystatin C was measured using Dade Behring N Latex Cystatin C assay and serum creatinine by an enzymatic method (Roche).

RESULTS

In the healthy subjects mean serum cystatin C was 0.70 mg/L (range 0.44-1.09) and mean serum creatinine 77 micromol/L (range 54-100). The analytical variance was 2.0% for cystatin C and 1.6% for creatinine. The intra-individual variance was greater for cystatin C than for creatinine (8.6% vs. 4.7%). The inter-individual variance was similar for both analytes (cystatin C 15.1% vs. creatinine 14.4%). In the patients with impaired renal function mean serum cystatin C was 1.86 mg/L (range 0.45-3.31) and mean serum creatinine 224 micromol/L (range 103-430). The analytical variance was 1.8% for cystatin C and 1.4% for creatinine. The intra-individual variance was greater for cystatin C than for creatinine (16.0% vs. 8.9%).

CONCLUSION

In the present study, the intra-individual variance was greater for cystatin C than for creatinine in both healthy subjects and in patients with impaired renal function. Accordingly, serum creatinine is the preferred marker for serial monitoring of renal function in individuals with stable muscle mass.

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.

Biochemistry and Clinical Role of Human Cystatin C

Low molecular-mass plasma proteins play a key role in health and disease. Cystatin C is an endogenous cysteine proteinase inhibitor belonging to the type 2 cystatin superfamily. The mature, active form of human cystatin C is a single non-glycosylated polypeptide chain consisting of 120 amino acid residues, with a molecular mass of 13,343-13,359 Da, and containing four characteristic disulfide-paired cysteine residues. Human cystatin C is encoded by the CST3 gene, ubiquitously expressed at moderate levels. Cystatin C monomer is present in all human body fluids; it is preferentially abundant in cerebrospinal fluid, seminal plasma, and milk. Cystatin C L68Q variant is an amyloid fibril-forming protein with a high tendency to dimerize. It forms self-aggregates with massive amyloid deposits in the brain arteries of young adults, leading to lethal cerebral hemorrhage. The main catabolic site of cystatin C is the kidney: more than 99% of the protein is cleared from the circulation by glomerular ultrafiltration and tubular reabsorption. The diagnostic value of cystatin C as a marker of kidney dysfunction has been extensively investigated in multiple clinical studies on adults, children, and in the elderly. In almost all the clinical studies, cystatin C demonstrated a better diagnostic accuracy than serum creatinine in discriminating normal from impaired kidney function, but controversial results have been obtained by comparing this protein with other indices of kidney disease, especially serum creatinine-based equations. In this review, we present and discuss most of the available data from the literature, critically reviewing conclusions and suggestions for the use of cystatin C in clinical practice. Despite the multitude of clinical data in the literature, cystatin C has not been widely used, perhaps because of a combination of factors, such as a general diffidence among clinicians, the absence of definitive cut-off values, conflicting results in clinical studies, no clear evidence on when and how to request the test, the poor commutability of results, and no accurate examination of costs and of its routine use in a stat laboratory.

Diagnostic Tools for Monitoring Kidney Transplant Recipients

Recent advancements in immunobiology have introduced several new diagnostic tools for monitoring kidney transplant recipients. These have been added to more established tests that, although imperfect, remain important benchmarks of diagnostic utility. Both new and old tests can be characterized with regard to their practicality, and as to whether they detect aberrant function or define the cause of dysfunction. Unfortunately, no current test is both practical and specific to a particular disease entity. Accordingly, the diagnosis of graft dysfunction remains dependent on the proper use and interpretation of many studies. This article reviews the current assays that have been evaluated in the clinic for the diagnosis of renal allograft-related diseases. These are limited to assays based on routinely obtainable samples such as blood, biopsy tissue, and urine. Newer studies are presented, along with more mundane assays, to highlight the practical use of studies regardless of their degree of mechanistic sophistication.

Sources of variation and reference intervals for serum cystatin C in a healthy Japanese adult population

BACKGROUND

To derive reference intervals (RIs) for cystatin C (CysC), we examined sources of variation in its serum concentration by multiple regression analysis.

METHODS

A total of 596 healthy subjects (30-75 years of age) who underwent an annual health check were chosen as candidate reference individuals who did not have any chronic illness requiring medication. Serum CysC was measured together with routine screening tests (basic clinical chemistry and complete blood count).

RESULTS

Multivariate analysis revealed that CysC concentrations were higher in males by an average of 0.082 mg/L. Levels were positively associated with age (+0.047 mg/L for every 10 years), body fat (BF%) and cigarette smoking, and negatively associated with alcohol consumption. A subgroup analysis revealed that the gender difference was not significant for those over 50 years of age. RIs were determined using a "latent abnormal values exclusion method" involving deletion of individuals with two or more abnormal results in the screening tests. RIs were partitioned into three categories by age and gender: 0.60-0.95 mg/L for males aged 30-50 years; 0.55-0.84 mg/L for females aged 30-50 years; and 0.64-1.05 mg/L for all subjects aged 51-75 years. Creatinine levels showed little age-related change, but a conspicuous gender difference; they increased with body weight, but not with BF%.

CONCLUSIONS

In interpreting serum CysC levels, BF%, cigarette smoking, and alcohol consumption may need to be considered, in addition to age and gender, as sources of variation.

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.

Could plasma cystatin C be useful as a marker of hemodialysis low molecular weight proteins removal?

BACKGROUND

Plasma cystatin (pCyst) is a well-assessed tool for measuring renal function, and it could also play a part in hemodialysis adequacy.

METHODS

pCyst and other uremic toxins (urea, creatinine, parathyroid hormone, prolactin) were assessed before and after a dialysis session in 18 hemodialysis patients: 7 on bicarbonate hemodialysis (BHD) and 11 on mixed convective dialysis (MCD; 6 standard hemodiafiltration and 5 acetate-free biofiltration). Plasma levels and reduction ratios (RR) were then compared between the BHD and MCD groups.

RESULTS

The mean pre-dialysis pCyst level is nearly the same in both groups (5.3 +/- 0.8 vs. 5.7 +/- 1 mg/l, p = ns), although a substantial decrease occurs after MCD only (mean 2.4 +/- 1 vs. 6.2 +/- 2.2 mg/l after BHD, p = 0.002). The mean pCyst RR (PCRR) of 55.5% after MCD is poorly related to prolactin and urea RR, fairly comparable to parathyroid hormone RR and very close to creatinine RR (58.4%).

CONCLUSIONS

Only MCD removes pCyst, but the amount of removal is different for other low molecular weight proteins (prolactin and parathyroid hormone) and similar for creatinine, a classic 'little molecule'. In view of the discrepancy of these findings, the use of pCyst in hemodialysis still seems premature and needs further studies.

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

OBJECTIVES

To evaluate the diagnostic significance of serum cystatin C levels in clinical practice.

DESIGN AND METHODS

Serum (99m)Tc-DTPA clearance was compared with serum cystatin C, creatinine, beta(2)-microglobulin levels and creatinine clearance in a group of patients aged 42.61 +/- 7.55 years with glomerular filtration rates of 10-60 mL/min/1.73 m(2) (n = 52) and healthy controls aged 43.90 +/- 12.06 years (n = 52).

RESULTS

No effect of sex on serum cystatin C levels was observed, but average levels increased with age. No significant difference was evident between the mean cystatin C levels of three blood samples taken at 1 month intervals from healthy subjects. Reference clearance was correlated with creatinine clearance (r = 0.957), cystatin C (r = 0.828), beta(2)-microglobulin (r = 0.767) and creatinine (r = 0.682). 60 mL/min/1.73 m(2) was chosen as the borderline for receiver-operating characteristics analysis. The values for the cut-off point, sensitivity, specificity and the area under curve were determined for cystatin C as 1.36 mg/L, 98%, 99% and 0.99 +/- 00.1, respectively; for creatinine, the values were 103 micromol/L, 80%, 100% and 0.97 +/- 0.01, respectively, and for beta(2)-microglobulin, the values were 2.51 mg/L, 86%, 92% and 0.94 +/- 0.02, respectively.

CONCLUSION

Serum cystatin C level can be used as a marker for renal damage.

Cystatin C-A novel marker of glomerular filtration rate: A review

Glomerular filtration rate is routinely assessed by measuring the serum markers such as urea nitrogen and serum creatinine. Although these markers are widely used to assess renal function but they do not perform optimally in certain clinical settings. There is thus a practical need for an easily automated alternative to plasma creatine, which would be more specific, sensitive and reliable from the analytical and clinical view point. Compared with the above endogenous markers, and time consuming laborious tests, Cystatin C facilitates the recognition of abnormal renal function in children, as its reference range is constant beyond the 1(st) year of life. This review mainly focuses on the diagnostic performance of Cystatin C against other renal markers in the pediatric population and in specific subpopulations of patients.

Biochemical indicators of cardiac and renal function in a healthy elderly population

OBJECTIVES

To examine the distributions of NT-proBNP and cystatin C and their relation to age, gender, and other physiological factors in an apparently healthy elderly population.

METHOD

NT-proBNP and cystatin C were analyzed in 407 and 408 healthy individuals, median age: 65 (range 40-76).

RESULTS

Increasing age, female gender and CRP were independently associated to higher NT-proBNP levels. Age, body mass index, and CRP level were independently associated to the cystatin C level. In women and men, < or =65 years, the 97.5th percentile value for NT-proBNP was 268 ng/l and 184 ng/l, in those older, 391 ng/l and 269 ng/l. For those < or =65 years the 97.5th percentile value for cystatin C was 1.12 mg/l, and for those older 1.21 mg/l.

CONCLUSION

In a healthy elderly population, NT-proBNP is influenced by age and gender, whereas cystatin C is influenced by age but not by gender. Both markers seem to be associated to the CRP level.

A sol particle homogeneous immunoassay for measuring serum cystatin C

OBJECTIVES

We have developed a sol particle immunoassay (SPIA) for measuring serum cystatin C, an endogenous marker of glomerular filtration rate (GFR).

DESIGN AND METHODS

We used colloidal gold particles coated with anti-cystatin C antibodies.

RESULTS

The assay was linear in the range 0.2 to 8 mg/L and showed good correlation between theoretical and obtained values. The within and between-day coefficients of variation (CV) varied from 1.1 to 1.6% and 0.4 to 1.0%, respectively. Analytical recovery was 95.7 to 103.7%. No interference could be detected from bilirubin (up to 200 mg/L), hemoglobin (up to 3 g/L), chyle (up to 5,000 FTU), rheumatoid factor (up to 1,000 IU/mL) or anticoagulants. Serum samples (n = 101), from which turbidity had been removed, were measured either with our assay or with Dako Cystatin C PET kits, using a Model 7070 Hitachi automatic clinical analyzer. Comparing these two methods, the calculated linear regression equation and the correlation coefficient were y = 0.986 x -0.153 and r = 0.995, respectively.

CONCLUSIONS

Our new SPIA assay is a fully automated, homogeneous immunoassay that can readily be used in conjunction with various commercial analyzers that are currently available. The assay is sensitive, precise and suitable for clinical use and appears to offer advantages over other GFR markers such as creatinine.

Proteinuria: The diagnostic strategy based on urine proteins differentiation

Basal glomerular membrane represents mechanical and electrical barrier for passing of the plasma proteins. Mechanical barrier is composed of cylindrical pores and filtration fissure, and negative layer charge in exterior and interior side of basal glomerular membrane, made of heparan sulphate and sialoglicoproteine, provides certain electrical barrier. Diagnostic strategy based on different serum and urine proteins enables the differentiation of various types of proteinuria. Depending on etiology of proteinuria it can be prerenal, renal and postrenal. By analyzing albumin, armicroglobulin, immunoglobulin G and armacroglobulin, together with total protein in urine, it is possible to detect and differentiate causes of prerenal, renal (glomerular, tubular, glomerulo-tubular) and postrenal proteinuria. The adequate and early differentiation of proteinuria type is of an immense diagnostic and therapeutic importance.

[Cystatin C as a measure of glomerular filtration in patients with kidney transplants]

INTRODUCTION

Assessment of renal function is of great importance in clinical medicine, especially in renal transplant patients requiring frequent controls of renal function. Therefore, continuous efforts have been made in searching precise and simple method for determination of glomerular filtration rate (GFR). Serum level of cystatin C (CyC), protein of low molecular weight, has been proposed as measure of GFR, but the data of its value in renal transplant patients are scarce [8-10].

PURPOSE

The aim of this study was to compare the serum levels of low molecular weight proteins CyC and beta 2-microglobulin (beta 2-MG) with creatinine clearance, as well known measure of GFR, in renal transplant patients and control group of patients with different renal disease.

PATIENTS AND METHODS

The study included 36 patients divided into two groups. Group 1: 20 renal transplant patients (12 men and 8 women) aged between 22 and 63 (40.4 +/- 10.1) years with creatinine clearance from 7.1 to 77.7 ml/min. Group 2: 16 controls (5 men and 11 women) with various renal diseases, aged between 24 and 63 (41.5 +/- 12.5) years with creatinine clearance from 60.5 to 116.8 ml/min. N Latex Cystatin C and beta 2-microglobulin for the Behring Nephelometer System was used in this study. Creatinine was determined with Jaffe-reaction in serum and urine.

RESULTS

In renal transplant patients as well as in control group of patients the significant correlation between creatinine clearance and reciprocal values of the serum CyC (rt = 0.828; pt < 0.001; rc = 0.603; pc < 0.05) and reciprocal values of the serum beta 2-MG levels (rt = 0.791; pt < 0.001; rc = 0.627; pc < 0.05) was found (Graph 1). There was a slightly better correlation between creatinine clearance and reciprocal values of the serum CyC than the one between creatinine clearance and reciprocal values of the serum beta 2-MG without statistical significance in renal transplant patients. There was no difference in correlation coefficients between both low molecular weight proteins and creatinine clearance in Group 2. The correlation coefficient between serum CyC and beta 2-MG was r = 0.839 (p < 0.001) in renal transplant patients and r = 0.835 (p < 0.05) in control group. There were no significant differences in correlation coefficients between reciprocal values of serum CyC and creatinine clearance (p = 0.2043) as well as reciprocal values of serum beta 2-MG and creatinine clearance (p = 0.3717) between Group 1 and Group 2.

DISCUSSION

In renal transplant patients rapid assessment of graft function is necessary. This allows early recognition of rejection as well as differential diagnosis of different renal graft disorders. Study of Risch and co [16] suggested that serum CyC was very good marker for GFR in renal transplant patients which was confirmed by the other authors too [20-22]. During inflammatory process or other pathological conditions, especially during acute rejection or infections. CyC also provided precise assessment of GFR while creatinine clearance varied dramatically [16]. Serum concentration of beta 2-MG, another low molecular weight protein, also depends both on its production rate and the GFR [5, 19]. Its production is dramatically different in patients with infections [5] as well as while immunosuppressive drugs are used [16]. Therefore, beta 2-MG is impractical as GFR marker in patients with renal transplants. So, serum CyC was considered as better marker for GFR than beta 2-MG and creatinine clearance in renal transplant patients with different complications [16]. In this study serum CyC was slightly better marker for GFR than beta 2-MG, without statistical significance (Graph 1). Renal transplant patients, however, were in the stable condition at the time of the study.

CONCLUSION

Serum CyC was moderately better marker of GFR than beta 2-MG in renal transplant patients when they were in the stable condition. Serum CyC and beta 2-MG were the same markers of GFR in control group of patients with various renal diseases. There was no significant difference in correlation coefficients between reciprocal values of the serum CyC and creatinine clearance (p = 0.2043) as well as reciprocal values of the serum beta 2-MG levels and creatinine clearance (p = 0.3717) between two examined groups of patients. The studies on renal transplant patients with acute graft rejection or infections are warranted.

Serum cystatin C and beta2-microglobulin as markers of glomerular filtration rate

Continuous efforts have been made to find out precise and simple method for determination of glomerular filtration rate (GFR). Cystatin C (cysteine proteinase inhibitor = CyC) is a low molecular weight (LMW) protein which is produced constantly by all nucleated cells independently of different pathological conditions and eliminated from the blood exclusively by glomeruli. So, CyC closely reflects the GFR. In the present study 75 patients aged between 18 and 74 (44.3 +/- 12.2) years were analyzed, with the aim to compare the reciprocal values of serum level of LMW proteins CyC and beta2-microglobulin (beta2-MG) with creatinine clearance (Ccr) as a measure of GFR. Patients were divided into groups according to sex, age (<60; >60 years) and renal diseases: patients with glomerulonephritis (GN) with and without nephrotic proteinuria, pyelonephritis (PyN), and renal transplant (Tx). High correlation between Ccr and 1/CyC (r = 0.81; p < 0.01) and Ccr and 1/beta2-MG (r = 0.80; p < 0.01) in all examined patients was found. There was significant correlation between Ccr and 1/CyC (0.82 vs. 0.79) and Ccr and 1/beta2-MG (0.85 vs. 0.76) in men as well in women, and also in two groups of patients formed according to the age (0.82 vs. 0.77; p < 0.01; 0.80 vs. 0.81; p < 0.01), without any statistical significant difference between the groups. In studied groups with different renal diseases, there were no differences in correlation coefficients between Ccr and 1/CyC and Ccr and 1/beta2-MG (p1 = 0.29; p2 = 0.21; p3 = 0.79; p4 = 0.43), without statistical differences between the groups, except significant difference in correlation coefficients for Ccr and 1/beta2-MG between patients with GN with and without nephrotic proteinuria (p < 0.032). LMW proteins, serum CyC and beta2-MG, are as good markers of GFR as Ccr, regardless sex and age. Both of these LMW proteins are good markers of GFR in patients with GN without nephrotic proteinuria, PyN and Tx patients. In patients with GN and nephrotic proteinuria serum CyC is a better marker of GFR than beta2-MG.

Serum cystatin C as a marker of the renal function in patients with spinal cord injury

OBJECTIVE

To investigate the relationship between serum cystatin C, serum creatinine, and (51)Cr-EDTA-clearance in patients with spinal cord injury.

SETTING

The Spinal Cord Unit, Viborg-Kjellerup County Hospital.

METHODS

Twenty-four men and seven women aged 20.3 to 68.0 years with motor complete spinal cord injury (ASIA A or B) were included. Serum cystatin C was measured by an automated particle-enhanced nephelometric immunoassay (Dade Behring), serum creatinine by an enzymatic method (Vitros 950), and (51)Cr-EDTA-clearance by a multiple plasma sample method.

RESULTS

A linear relationship was found between (51)Cr-EDTA-clearance and the reciprocal values of cystatin C and creatinine. The correlation coefficient between (51)Cr-EDTA-clearance and 1/cystatin C was 0.72 compared to the correlation coefficient between (51)Cr-EDTA-clearance and 1/creatinine being 0.26. Comparison of the area under the curves in the non-parametric receiver operating characteristics (ROC) plots for serum cystatin C (area under the curve (AUC)=0.912; SE=0.065), and serum creatinine (AUC=0.507; SE=0.115) revealed significant differences (P-values=0.0005).

CONCLUSION

In patients with spinal cord injury serum cystatin C is a better marker of the renal function compared to serum creatinine.

[Cystatin C and small molecular mass proteins as new markers for determination of glomerular filtration rate]

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Determination of serum cystatin C: biological variation and reference values

Human cystatin C is a low molecular weight protein which has been proposed as a better marker of glomerular filtration rate than creatinine. To be able to interpret results obtained in different patient populations it is necessary to define cystatin C reference values. We measured serum concentration of cystatin C in 1223 subjects using a particle-enhanced nephelometric assay. Subjects were aged 4 to 79 years and were selected among apparently healthy individuals who came to the Centre for Preventive Medicine in Vandoeuvre-Lès-Nancy, France. We observed a Gaussian distribution of cystatin C concentration in serum. We did not find any effect of age or gender in children, hormonal status in women (puberty, menopause, oral contraceptives or hormone replacement therapy) or alcohol intake. Cystatin C concentration was slightly lower in female than in male adults below the age of 60 years. Cystatin C levels significantly increased above the age of 60 in both males and females, probably due to physiological aging of renal function. No other significant differences were observed between males and females. Using multiple regression analysis, moderate correlations were observed between body mass index and cystatin C, and between smoking and cystatin C, but these were not biologically significant. According to the literature, only methylprednisolone and cyclosporin A increased and decreased cystatin C levels, respectively. The reference values for cystatin C obtained in a carefully selected population were 0.75+/-0.089 mg/l for children aged 4-19 years, 0.74+/-0.100 mg/l for males and 0.65+/-0.085 mg/l for females (aged 20-59 years), and 0.83+/-0.103 mg/l for older individuals (> or =60 years).

Exercise alters serum pneumoprotein concentrations

To determine the effect of exercise on serum levels of Clara cell protein (CC16) and surfactant-associated protein A (SP-A), serum was collected from 14 healthy subjects 1 h after maximal and sub-maximal exercise. Healthy volunteers participated on separate occasions in a control (no exercise) session, simulated firefighting tasks for 30 min (n=14), and intermittent treadmill exercise at near maximal heart rates for 60 min (n=10). Serum samples and induced sputum samples were collected 1 h post exercise. Induced sputum fluid was analyzed for tumor necrosis factor alpha (TNF-alpha), an inflammatory mediator produced by pulmonary macrophages. Serum CC16 levels increased significantly with both firefighting tasks (15+/-13 microg/L vs. 9+/-4 microg/L, P=0.047) and treadmill exercise (15+/-8 microg/L vs. 9+/-4 microg/L, P<0.01). Serum SP-A concentrations did not change compared to control with either firefighting tasks (247+/-106 microg/L vs. 247+/-96 microg/L, P=0.84) or treadmill exercise (251+/-89 microg/L vs. 285+/-87 microg/L, P=0.44). TNF-alpha concentrations in sputum supernatant showed no significant difference from controls. These results show an increase in serum CC16 after exercise. This must be considered when utilizing serum CC16 to determine the presence of lung injury in settings that combine exercise and toxic exposures.

Serum cystatin C, a potent inhibitor of cysteine proteinases, is elevated in asthmatic patients

The effect of asthma pathogenesis on serum cystatin C, a potent inhibitor of cysteine proteinases and a newly proposed marker of the renal function, has not been yet determined. The objectives were to determine the 24-h pattern of cystatin C and creatinine concentrations in sera of asthmatic patients in order to test whether their concentrations might reflect circadian rhythms, the disease severity and the effect of therapy. Serum concentrations of cystatin C and creatinine were determined in steroid-independent and steroid-dependent asthmatics before and after 1 week of treatment with methylprednisolone and cyclosporin A, respectively. Samples were collected every 4 h during a 24-h period. Little or no significant effects of time on cystatin C and creatinine concentrations over a 24-h period were observed in healthy and asthmatic sera. However, significantly higher cystatin C concentrations were found in asthmatic patients compared to controls which suggests its role in the pathogenesis of asthma. Methylprednisolone increased and cyclosporin A decreased serum cystatin C concentrations after 1 week of therapy. Additionally these results support the need for the evaluation of cystatin C as a marker of glomerular filtration rate determination in asthma.

Developments in the assessment of glomerular filtration rate

The assessment of the glomerular filtration rate (GFR) is the most commonly used test of renal function. The accepted reference procedure employs an exogenous clearance marker whilst the most popular test is that of serum or plasma creatinine. All of these tests have limitations, although the surrogate endogenous markers are the most practical. Cystatin C, a low molecular weight protein which can be measured by light scattering immunoassay, possesses many of the attributes required of the ideal GFR marker. Data on reference ranges indicate that circulating cystatin C levels reflect the variation in GFR throughout life and the marker demonstrates a better correlation with the reference procedure than serum creatinine.

Serum cystatin C as an endogenous marker of the renal function--a review

Since 1985, cystatin C has been suggested to be a marker of the renal function. Cystatin C is a proteinase inhibitor with a low molecular weight (M(r) = 13359). It is produced at a constant rate in all nucleated cells investigated to date, freely filtered in the renal glomeruli and reabsorbed and catabolised in the proximal tubules. The concentration of serum cystatin C is mainly determined by glomerular filtration, which makes cystatin C an endogenous marker of glomerular filtration rate (GFR). There are few data describing the influence of various factors on the production and elimination of cystatin C. Fully automated assays using particle-enhanced turbidimetry or particle-enhanced nephelometry are available and the assays are precise, rapid and usable in clinical routine practice. Reference intervals have been determined for cystatin C in adults and in children older than one year. It has been suggested that the same reference interval can be used in children older than one year and in adults without gender differences, on the assumption that the same method with the same standardisation is used. Several studies including adults and children with different renal diseases with various kidney function have suggested serum cystatin C to be a better marker of GFR than serum creatinine.