Particle enhanced turbidimetric immunoassay for the determination of urine cystatin C on Cobas c501

Detection of urinary cystatin-c in IUGR neonates by immunoblot SDS-PAGE

BACKGROUND

it is known that intrauterine growth retardation (IUGR) represents a risk factor for the deterioration of renal function as it can adversely impact on the number of nephrons developed in the kidney during nephrogenesis. An interesting molecule is the Cystatin-C (cyst-C): it is considered to have the potency to detect both glomerular and proximal renal injury. Recently, using a quantitative EIA cyst-C detection kit, we found increased levels of cyst-C in the urine of neonates with IUGR. Since cyst-C molecules can be present in both monomer and/or polymer forms, the purpose of this study is to investigate in which forms this molecule is present in the urine of IUGR neonates by Immunoblot SDS-PAGE in order to verify if the presence or absence of a particular type of cyst-C conformation can give more information about the renal functioning.

METHODS

urine samples were collected from 64 neonates with IUGR, and 86 healthy controls defined as appropriate for gestational age (AGA). Urinary cyst-C was investigated by the Immunoblot SDS-PAGE.

RESULTS

in all urine samples, SDS-PAGE analysis showed a reactivity of the IgG anti cyst-C with a complex of about 70 kDa. The monomer form at 13 KDa appeared in 78% of IUGR neonates and in 12% of AGA neonates.

CONCLUSIONS

this study revealed the presence of monomer cyst-C in the urine of IUGR neonates, and suggests an insufficient and/or non-compensatory reabsorption by tubular cells. Monomeric cyst-C can be considered an early biochemical marker to identify and to select IUGR neonates who need to be monitored for risk of renal injury.

COVID-19 patients in intensive care develop predominantly oliguric acute kidney injury

Background

Acute kidney injury (AKI) is a syndrome of reduced glomerular filtration rate and/or reduced urine flow associated with mortality in corona virus disease 2019 (COVID‐19). AKI is often associated with renal tissue damage, which may lead to chronic kidney disease. Biomarkers of tissue damage may identify patients of particular risk.

Methods

In a prospective observational study of 57 patients admitted to intensive care, AKI incidence and characteristics was evaluated according to KDIGO criteria and related to days after admission. Urinary albumin, Neutrophil Gelatinase‐Associated Lipocalin (NGAL), Kidney Injury Molecule 1 (KIM‐1) and Plasma Tissue Inhibitor of MetalloProteinase 2 (TIMP‐2) were analysed in 52 patients at admission.

The majority (n = 51, 89%) of patients developed AKI, and 27 (47%) patients had predominantly oliguric AKI where oliguria was more severe than plasma Creatinine increase. Severe oliguria within first 2 days after admission was common (n = 37, 65%), whereas stage 2 and 3 AKI due to Creatinine occurred later than day 2 in 67% (12/18) of cases. Renal replacement therapy was started in 9 (16%) patients, and 30‐day mortality was 28%. Urinary biomarkers were increased in a majority of patients, but did not robustly predict KDIGO stage. Most patients had microalbuminuria, and severe albuminuria (albumin Creatinine ratio > 30 mg/mmol) was found in n = 9 (17%) patients.

Conclusions

A majority of patients with COVID‐19 admitted to the ICU develop AKI. The functional deficit is often low urinary volume, and initial levels of biomarkers are generally increased without clear relation to final AKI stage.

Day-to-day variation of the kidney proximal tubular injury markers urinary cystatin C, KIM1, and NGAL in patients with chronic kidney disease

Background: It is important to know the intraindividual variation of biomarkers to be able to distinguish a change of a biomarker due to the course of the disease from the normal biological variation of the marker. The purpose of this study was to investigate the day-to-day variability of urine markers in nephrology patients.Materials: 23 nephrology patients were included in the study. First morning urine samples were collected daily for ten consecutive days and analyzed for U-cystatin C, U-KIM1, U-NGAL and U-creatinine. The day-to-day variation was calculated as concentrations of the markers and as creatinine ratios. Values deviating more than the 90^th percentile of the normal intraindividual variation was used to define a disease/treatment specific change.Results: The day-to-day coefficient of variation (CV) for individual patients varied between 9.6 and 100.3% for NGAL (mean 45.6%) and between 8.8 and 107.3% for the NGAL/creatinine ratio (mean 43.8%). The corresponding values for KIM1 were between 10.9 and 60.2% (mean 30.1%) and for the ratio between 8.7 and 59.8% (mean 23.4%) and for cystatin C 3.8-67.4% (mean 25.0%) and for the cystatin C/creatinine ratio 5.9-78.4% (mean 24.8%).Conclusions: The similar intraindividual CV values between the renal tubules damage markers and their corresponding creatinine ratios speaks against using creatinine ratio. Using the 90^th percentiles of the CV values as a limit for clinical change means that NGAL has to change by 83.3%, KIM1 by 45.5% and Cystatin C by 46.3% before the change can be considered clinically significant in patients with chronic kidney disease.

The validation of immunoblot SDS-PAGE as a qualitative and quantitative method for the determination of urinary Cystatin C in neonates

INTRODUCTION

The quantitative determination of urinary Cystatin C (cyst-C) associated with the qualitative analysis of its polymorphisms is an excellent method for early identification of newborns predisposed to renal function impairment. PETIA, PENIA and EIA are the immunometric methods used for the quantitative determination of cyst-C in human biologic fluid but they have limitations and do not allow qualitative analysis. The present study is a validation of Immunoblot SDS-PAGE for the qualitative and quantitative analysis of urinary cyst-C.

METHODS

Urine was collected from neonates in the nursey at S. Maria della Misericordia Hospital. Urinary cyst-C was investigated by the immunoblot SDS-PAGE and by reading of optical density.

RESULTS

The qualitative analysis showed two different molecular forms: a reactivity at about 70 KDa in all samples and a reactivity at 13 KDa in a limited number of samples. This analysis allows the correlation of the polymorphisms of cyst-C with specific alterations of renal function in newborns. The quantitative analysis is specific, sensitive and accurate. In fact the coefficient of variation for assay precision was 10% and for assay accuracy was ±10%, the detection limit was 0.009 ng/ µL and the calibration line has satisfactory linearity (range 0.02-0.3 ng/ µL). The stability of urinary cyst-C was acceptable, even without the use of protease inhibitors, as long as the assay was performed on freshly recruited urine or immediately after thawing the samples, which had been stored for up to six months.

CONCLUSION

Immunoblot SDS-PAGE analysis is a valid method of obtaining a qualitative and quantitative analysis of urinary cyst-C. This method presents unique information about a previously unknown 70 KDa cyst-C form. The assay may offer potential diagnostic information not available with immunometric method.

The future for diagnostic tests of acute kidney injury in critical care: evidence synthesis, care pathway analysis and research prioritisation

BACKGROUND

Acute kidney injury (AKI) is highly prevalent in hospital inpatient populations, leading to significant mortality and morbidity, reduced quality of life and high short- and long-term health-care costs for the NHS. New diagnostic tests may offer an earlier diagnosis or improved care, but evidence of benefit to patients and of value to the NHS is required before national adoption.

OBJECTIVES

To evaluate the potential for AKI in vitro diagnostic tests to enhance the NHS care of patients admitted to the intensive care unit (ICU) and identify an efficient supporting research strategy.

DATA SOURCES

We searched ClinicalTrials.gov, The Cochrane Library databases, Embase, Health Management Information Consortium, International Clinical Trials Registry Platform, MEDLINE, metaRegister of Current Controlled Trials, PubMed and Web of Science databases from their inception dates until September 2014 (review 1), November 2015 (review 2) and July 2015 (economic model). Details of databases used for each review and coverage dates are listed in the main report.

REVIEW METHODS

The AKI-Diagnostics project included horizon scanning, systematic reviewing, meta-analysis of sensitivity and specificity, appraisal of analytical validity, care pathway analysis, model-based lifetime economic evaluation from a UK NHS perspective and value of information (VOI) analysis.

RESULTS

The horizon-scanning search identified 152 potential tests and biomarkers. Three tests, Nephrocheck^® (Astute Medical, Inc., San Diego, CA, USA), NGAL and cystatin C, were subjected to detailed review. The meta-analysis was limited by variable reporting standards, study quality and heterogeneity, but sensitivity was between 0.54 and 0.92 and specificity was between 0.49 and 0.95 depending on the test. A bespoke critical appraisal framework demonstrated that analytical validity was also poorly reported in many instances. In the economic model the incremental cost-effectiveness ratios ranged from £11,476 to £19,324 per quality-adjusted life-year (QALY), with a probability of cost-effectiveness between 48% and 54% when tests were compared with current standard care.

LIMITATIONS

The major limitation in the evidence on tests was the heterogeneity between studies in the definitions of AKI and the timing of testing.

CONCLUSIONS

Diagnostic tests for AKI in the ICU offer the potential to improve patient care and add value to the NHS, but cost-effectiveness remains highly uncertain. Further research should focus on the mechanisms by which a new test might change current care processes in the ICU and the subsequent cost and QALY implications. The VOI analysis suggested that further observational research to better define the prevalence of AKI developing in the ICU would be worthwhile. A formal randomised controlled trial of biomarker use linked to a standardised AKI care pathway is necessary to provide definitive evidence on whether or not adoption of tests by the NHS would be of value.

STUDY REGISTRATION

The systematic review within this study is registered as PROSPERO CRD42014013919.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Analytical performances of PENIA and PETIA urinary cystatin C determination allow tubular injury investigation

Background

The study was designed to evaluate the analytical performances of two ERM-DA471/IFCC traceable cystatin C (CysC) reagents available on the market for urinary CysC (u-CysC) quantification. In addition, clinical relevance was assessed by measuring u-CysC in healthy controls and in patients with tubular dysfunction.

Methods

CysC in urine was measured by a particle-enhanced nephelometric immunoassay using Siemens reagents and by a particle-enhanced turbidimetric immunoassay using DiaSys reagents. Imprecision, linearity, limit of detection and limit of quantification were evaluated according to CLSI recommendations. The two methods were tested on 150 urinary samples from 50 healthy subjects, 50 HIV patients with tubular dysfunction and 50 patients who developed acute kidney acute injury.

Results

Within-laboratory coefficients of variations were below 4%. The lower limit of quantification of the assay was found at 0.043 and 0.046 mg/L for DiaSys and Siemens, respectively. The following Passing-Bablok regression equations were obtained: DiaSys = 0.99 Siemens + 0.00. Using Bland-Altman analysis, the mean bias was –0.004 mg/L on the analytical range between 0.02 and 1 mg/L. Median u-CysC in 50 HIV patients with tubular dysfunction and in 50 patients with AKI was higher than in control subjects.

Conclusions

Both Siemens and DiaSys reagents demonstrated reliable and reproducible performances allowing easy determination of u-CysC on automated platforms in clinical practice with potential interest for the detection of tubular dysfunction.

Novel automated immune turbidimetric assay for routine urinary cystatin-C determinations

AIM

There is no commercially available urinary cystatin-C (u-CYSC) test in the market. Therefore, we optimized and validated an automated immune turbidimetric test for u-CYSC measurements and investigated u-CYSC concentrations in acute and chronic diseases which might lead to renal tubular disorders.

MATERIALS & METHODS

A particle-enhanced immune turbidimetric assay was adapted and validated on a Cobas 8000/c502 analyzer. Urine samples of different patient groups were also analyzed.

RESULTS

Our method showed excellent analytical performance. U-CYSC/u-creatinine (u-CREAT) was higher in sepsis-related acute kidney injury group (p < 0.001) compared with controls and to patients with chronic hypertension and Type 2 diabetes.

CONCLUSION

We validated a fast, sensitive, fully automated u-CYSC assay which is ideal for routine use and might be a potential complementary laboratory test to evaluate renal tubular function.

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.

Correlation of Cystatin-C and radionuclidic measurement method of glomerular filtration rate in patients with lung cancer receiving cisplatin treatment

OBJECTIVE

Cisplatin is a chemotherapeutic agent which affects renal functions adversely. The best indicator of renal functions is glomerular filtration rate (GFR) measurement. Cystatin-C appears to be a good alternative to existing methods of measuring GFR. However, it is controversial whether Cystatin-C demonstrates GFR correctly for patients receiving chemotherapy. This study aimed to investigate the correlation between GFR values calculated by Cystatin-C based formulas, radionuclidic method (multiple blood sampling) and blood Cystatin-C values in patients with lung cancer, receiving cisplatin treatment in both pre-treatment and post-treatment periods.

MATERIALS AND METHODS

Thirty-six patients with lung cancer who were going to receive cisplatin treatment were included in this study. However, the evaluation was performed with 20 patients since 16 of them could not complete the treatment. Blood Cystatin-C values, GFR values calculated via Cystatin-C based formulas, and radionuclidic method were investigated before and after the cisplatin treatment.

RESULTS

After treatment significant decreases were detected in GFR values, obtained via radionuclidic measuring method. However, there was no significant difference in Cystatin-C values between pre-treatment and post-treatment periods. Also GFR values obtained by Cystatin-C based formulas were not significantly different in pre-treatment and post-treatment periods. There were meaningful correlations between radionuclidic method and Cystatin-C values and Cystatin-C based formulas before treatment. However, all correlations disappeared after the treatment.

CONCLUSION

GFR values, calculated by Cystatin-C may not be reliable in following renal functions in patients receiving chemotherapy. When reliable monitoring of the renal functions is necessary radionuclidic method may be preferred in these patients.

Multicenter study of creatinine- and/or cystatin C-based equations for estimation of glomerular filtration rates in Chinese patients with chronic kidney disease

Objective

To establish equations for the estimation of glomerular filtration rates (eGFRs) based on serum creatinine (SCr) and/or serum cystatin C (SCysC) in Chinese patients with chronic kidney disease (CKD), and to compare the new equations with both the reference GFR (rGFR) and the literature equations to evaluate their applicability.

Methods

The 788 Chinese CKD patients were randomly divided into two groups, the training group and the testing group, to establish new eGFR-formulas based on serum CysC and to validate the established formulas, respectively. ^99mTc-DTPA clearance (as the rGFR), serum Cr, and serum CysC were determined for all patients, and GFR was calculated using the Cockcroft-Gault equation (eGFR1), the MDRD formula (eGFR2), the CKD-EPI formulas (eGFR3, eGFR4), and the Chinese eGFR Investigation Collaboration formulas (eGFR5, eGFR6). The accuracy of each eGFR was compared with the rGFR.

Results

The training and testing groups' mean GFRs were 50.84±31.36 mL/min/1.73 m² and 54.16±29.45 mL/min/1.73 m², respectively. The two newly developed eGFR formulas were fitted using iterative computation: and . Significant correlation was observed between each eGFR and the rGFR. However, proportional errors and constant errors were observed between rGFR and eGFR1, eGFR2, eGFR4, eGFR5 or eGFR6, and constant errors were observed between eGFR3 and rGFR, as revealed by the Passing & Bablok plot analysis. The Bland-Altman analysis illustrated that the 95% limits of agreement of all equations exceeded the previously accepted limits of <60 mL/min •1.73 m², except the equations of eGFR7 and eGFR8.

Conclusion

The newly developed formulas, eGFR7 and eGFR8, provide precise and accurate GFR estimation using serum CysC detection alone or in combination with serum Cr detection. Differences in detection methods should be carefully considered when choosing literature eGFR equations to avoid misdiagnosis and mistreatment.