GFR estimates using cystatin C are superior to serum creatinine in adult patients with cystic fibrosis

Time to Rethink the Current Paradigm for Assessing Kidney Function in Drug Development and Beyond

Chronic kidney disease (CKD) is an important health issue that affects ~ 9.1% of the world adult population. Serum creatinine is the most commonly used biomarker for assessing kidney function and is utilized in different equations for estimating creatinine clearance or glomerular filtration rate (GFR). The Cockcroft-Gault formula for adults and "original" Schwartz formula for children have been the most commonly used equations for estimating kidney function during the last 3-4 decades. Introduction of standardized serum creatinine bioanalytical methodology has reduced interlaboratory variability but is not intended to be used with Cockcroft-Gault or original Schwartz equations. More accurate equations (for instance, Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) for adults and bedside Schwartz or Chronic Kidney Disease in Children Schwartz equation for children) based on standardized serum creatinine values (and another biomarker-cystatin C) have been introduced and validated in recent years. Recently, the CKD-EPI equation refitted without a race variable was introduced. Clinical practice guidance in nephrology advocates a shift to these equations for managing health care of patients with CKD. The guidance also recommends use of albuminuria in addition to GFR for CKD diagnosis and management. Significant research with large data sets would be necessary to evaluate whether this paradigm would also be valuable in drug dose adjustments. This article attempts to highlight some important advancements in the field from a clinical pharmacology perspective and is a call to action to industry, regulators, and academia to rethink the current paradigm for assessing kidney function to enable dose recommendation in patients with CKD.

Kidney and combined kidney and pancreas transplantation may be under-utilized in cystic fibrosis

Cystic fibrosis (CF) is a multisystem disorder and represents the most common inherited condition leading to death in Western countries. Previous reports of chronic kidney disease (CKD) in CF focus on cases post lung, or other solid organ, transplantation but CKD in CF patients pre transplantation is increasingly recognized as a challenging complication of CF. CKD can evolve as a sequel to acute kidney injury for example after prolonged treatment with aminoglycoside antibiotics during episodes of infection. Nephrolithiasis, diabetic nephropathy and a variety of glomerular lesions, such as amyloidosis and Immunoglobulin A nephropathy are also seen. Muscle depletion is common in CF, hence creatinine-based estimates of kidney function may underestimate the degree of renal impairment and lead to delayed diagnosis and management. Improved treatment options for CF patients have resulted in a sustained increase in life expectancy with increasing numbers of CF patients with CKD approaching end-stage renal failure prior to consideration of lung transplantation. We believe that kidney or combined kidney-pancreas transplantation are under-utilized in this population. We provide a brief primer on the landscape of CF and CKD and discuss transplant options. Suitable patients with CF and advanced CKD should be formally assessed for kidney or kidney-pancreas transplantation.

Altered intravenous drug disposition in people living with cystic fibrosis: A meta‐analysis integrating top‐down and bottom‐up data

Cystic fibrosis (CF) has been linked to altered drug disposition in various studies. However, the magnitude of these changes, influencing factors, and underlying mechanisms remain a matter of debate. The primary aim of this work was therefore to quantify changes in drug disposition (top‐down) and the pathophysiological parameters known to affect pharmacokinetics (PKs; bottom‐up). This was done through meta‐analyses and meta‐regressions in addition to theoretical PK simulations. Volumes of distribution and clearances were found to be elevated in people living with CF. These increases were larger in studies which included patients with pulmonary exacerbations. Differences in clearance were smaller in more recent studies and when results were normalized to body surface area or lean body mass instead of body weight. For the physiological parameters investigated, measured glomerular filtration rate and serum cytokine concentrations were found to be elevated in people living with CF, whereas serum albumin and creatinine levels were decreased. Possible pathophysiological mechanisms for these alterations relate to renal hyperfiltration, increases in free fraction, and inflammation. No differences were detected for cardiac output, body fat, fat free mass, hematocrit, creatinine clearance, and the activity of drug metabolizing enzymes. These findings imply that, in general, lower total plasma concentrations of drugs can be expected in people living with CF, especially when pulmonary exacerbations are present. Given the potential effect of CF on plasma protein binding and the variability in outcome observed between studies, the clinical relevance of adapting existing dosage regimens should be evaluated on a case‐by‐case basis.

Renal Function in Patients with Cystic Fibrosis: A Single-Center Study

Cystic fibrosis (CF) is the most common incurable autosomal recessive disease affecting the Caucasian population. As the prognosis for life extension of CF patients improves, co-morbidities, including kidney disease, become more common. Identifying those at the highest risk of kidney injury is therefore extremely important. The aim of this study was to evaluate the biomarkers of renal function in 50 CF patients using the estimated glomerular filtration rate (eGFR) based on creatinine and cystatin C equation as well as serum creatinine (sCr), serum cystatin C (CysC), serum urea and urinary neutrophil gelatinase-associated lipocalin (uNGAL) concentrations. sCr, CysC, urea and uNGAL were estimated. eGFR was calculated according to the CKD-EPI formula. CysC was significantly increased, while eGFR was significantly lower in the CF group than in the controls (p < 0.001 and p < 0.01, respectively). There was no significant difference in the sCr, urea and uNGAL concentrations between patients with CF and healthy subjects. For the purpose of our analysis, in order to assess renal function in patients with CF in clinical practice, the concentration of serum CysC and eGFRCKD-EPI should be determined. Patients with CF presented with renal function impairment pictured by increased serum CysC and decreased eGFR values compared to controls. Unchanged uNGAL concentrations suggested preserved tubular function despite aminoglycoside treatment. Further prospective studies are needed to clarify whether kidney impairment observed in the course of CF progresses.

Development of an Approach of High Sensitive Chemiluminescent Assay for Cystatin C Using a Nanoparticle Carrier

Cystatin C is an important cysteine protease inhibitor in the human body and is proposed as a new indicator of glomerular filtration rate for the detection of kidney damage. In this article, we report an ultra-sensitive, simple, and rapid chemiluminescence immunoassay method for cystatin C detection using functionalized mesoporous silica nanoparticles. After a three step hydrolysis, the amino-functionalized MSN encapsulating dye resulted in a hydrophobic environment for fixing the dye and amino groups for biological modification. The NaIO₄ immobilization method maintained the activity of the antibody notably well. The sandwich immunoassay using two monoclonal antibodies was chosen for its selectivity. The analysis demonstrated that the detection upper was 0.0029 ng/mL and linear relationship within the range of 0.0035-0.5 ng/mL (R ² = 0.9936). The relative standard deviation (RSD) for 11 parallel measurements of 0.25 ng/mL CysC was 4.7%. The automated chemiluminescence analyzer could detect 96 wells continuously. The results demonstrated that this method is ultra-sensitive, simple, and rapid for detecting cystatin C.

Optimizing Estimated Glomerular Filtration Rate to Support Adult to Pediatric Pharmacokinetic Bridging Studies in Patients with Cystic Fibrosis

BACKGROUND

The estimated glomerular filtration rate (eGFR) is often used to model drug clearance (CL) and scale doses across age and body size. Over their lifetime, patients with cystic fibrosis (CF) receive repeated courses of tobramycin, an antibiotic with eGFR-dependent CL, for the treatment of pulmonary exacerbations. Tobramycin population pharmacokinetic (PK) modeling can be used to decipher the best approach to define eGFR for pediatric bridging studies.

METHODS

Inpatients with CF who received intravenous tobramycin between 1 January 2006 and 30 May 2018 were eligible for inclusion. Encounters without tobramycin concentration measurement or missing covariate data were excluded. Population PK analysis was performed using NONMEM.Covariate models were built  following identification of the base model, with specific emphasis on the effect of different methods of estimating renal function as a covariate of tobramycin CL.

RESULTS

A total of 296 CF patients contributed 1029 care encounters (420 pediatric, 609 adult) and 4352 tobramycin concentrations to this analysis. The median (minimum, maximum) age at encounter was 19 years (0.2, 60), with serum creatinine of 0.60 mg/dL (0.10, 3.41). A two-compartment model best described the observed data, with height and eGFR as significant covariates of tobramycin CL. eGFR was best modeled using a combination of the modified Schwartz and Chronic Kidney Disease Epidemiology Collaboration (CKDEPI) equations expressed in absolute units.

CONCLUSIONS

The CKDEPI equation bridges PK data generated in adults to adolescents with CF better than the current regulatory standard. The eGFR should be expressed in absolute units (mL/min) for PK analyses.

Cystatin C: A Primer for Pharmacists

Pharmacists are at the forefront of dosing and monitoring medications eliminated by or toxic to the kidney. To evaluate the effectiveness and safety of these medications, accurate measurement of kidney function is paramount. The mainstay of kidney assessment for drug dosing and monitoring is serum creatinine (SCr)-based estimation equations. Yet, SCr has known limitations including its insensitivity to underlying changes in kidney function and the numerous non-kidney factors that are incompletely accounted for in equations to estimate glomerular filtration rate (eGFR). Serum cystatin C (cysC) is a biomarker that can serve as an adjunct or alternative to SCr to evaluate kidney function for drug dosing. Pharmacists must be educated about the strengths and limitations of cysC prior to applying it to medication management. Not all patient populations have been studied and some evaluations demonstrated large variations in the relationship between cysC and GFR. Use of eGFR equations incorporating cysC should be reserved for drug management in scenarios with demonstrated outcomes, including to improve pharmacodynamic target attainment for antibiotics or reduce drug toxicity. This article provides an overview of cysC, discusses evidence around its use in medication dosing and in special populations, and describes practical considerations for application and implementation.

Estimation of GFR in Patients With Cystic Fibrosis: A Cross-Sectional Study

Background

Patients with cystic fibrosis (CF) have frequent infectious complications requiring nephrotoxic medications, necessitating monitoring of renal function. Although adult studies have suggested that cystatin C (CysC)-based estimated glomerular filtration rate (eGFR) may be preferable due to reduced muscle mass of patients with CF, pediatric patients remain understudied.

Objective

Our objective was to determine which eGFR formula is best for estimating glomerular filtration rate (GFR) in pediatric patients with CF.

Methods

A total of 17 patients with CF treated with nephrotoxic antibiotics were recruited from the Children's Hospital at London Health Sciences Centre, London, Ontario, Canada. ⁹⁹Tc DTPA GFR (measured GFR [mGFR]) was measured with 4-point measurements starting at 120 minutes using a 2-compartmental model with Brøchner-Mortensen correction, with simultaneous measurement of creatinine, urea, and CysC. The eGFR was calculated using 16 known equations based on creatinine, urea, CysC, or combinations of these. Primary outcome measures were correlation with mGFR, and agreement within 10% for various eGFR equations.

Results

Mean mGFR was 136 ± 21 mL/min/1.73 m². Mean creatinine, CysC, and urea were 38 ± 10 μmol/L, 0.72 ± 0.08 mg/L, and 3.9 ± 1.4 mmol/L, respectively. The 2014 Grubb CysC eGFR had the best correlation coefficient (r = 0.75, P = .0004); however, only 35% were within 10%. The new Schwartz formula with creatinine and urea had the best agreement within 10%, but a relatively low correlation coefficient (r = 0.63, P = .0065, 64% within 10%).

Conclusions

Our study suggests that none of the eGFR formulae work well in this small cohort of pediatric patients with CF with preserved body composition, possibly due to inflammation causing false elevations of CysC. Based on the small numbers, we cannot conclude which eGFR formula is best.

Pyruvate Kinase M2: A Novel Biomarker for the Early Detection of Acute Kidney Injury

The identification of biomarkers for the early detection of acute kidney injury (AKI) is clinically important. Acute kidney injury (AKI) in critically ill patients is closely associated with increased morbidity and mortality. Conventional biomarkers, such as serum creatinine (SCr) and blood urea nitrogen (BUN), are frequently used to diagnose AKI. However, these biomarkers increase only after significant structural damage has occurred. Recent efforts have focused on identification and validation of new noninvasive biomarkers for the early detection of AKI, prior to extensive structural damage. Furthermore, AKI biomarkers can provide valuable insight into the molecular mechanisms of this complex and heterogeneous disease. Our previous study suggested that pyruvate kinase M2 (PKM2), which is excreted in the urine, is a sensitive biomarker for nephrotoxicity. To appropriately and optimally utilize PKM2 as a biomarker for AKI requires its complete characterization. This review highlights the major studies that have addressed the diagnostic and prognostic predictive power of biomarkers for AKI and assesses the potential usage of PKM2 as an early biomarker for AKI. We summarize the current state of knowledge regarding the role of biomarkers and the molecular and cellular mechanisms of AKI. This review will elucidate the biological basis of specific biomarkers that will contribute to improving the early detection and diagnosis of AKI.

Comparison of equations with estimate renal function to predict serum vancomycin concentration in patients with spinal cord injury--does the use of cystatin C improve accuracy?

BACKGROUND

Vancomycin dose selection is challenging in the spinal cord injury (SCI) population because of the difficulty in accurately estimating the renal function. Creatinine-based equations have been shown to be unreliable in this patient population. Adjusted equations designed for patients with SCI have not been well studied. Cystatin C is an alternative marker of renal function that is less affected by muscle mass and may offer improvement in estimating renal function leading to improved initial dose selection.

OBJECTIVE

To compare the accuracy of serum creatinine- and serum cystatin C-based equations used in a pharmacokinetic (PK) model to predict steady-state serum vancomycin concentration in an SCI population. The rationale for this study is the need for an improved predictive model to guide initial vancomycin dose design before the availability of a measured steady-state serum concentration.

METHODS

Patients with SCI receiving vancomycin with measured serum creatinine, cystatin C, and steady-state serum vancomycin concentration were identified. Serum creatinine- and cystatin C-based equations to estimate renal function were substituted into a population-based PK model to predict steady state-serum vancomycin concentration. Predictions using each equation in the model were compared with the measured steady-state serum vancomycin concentration. Predictive performances using each equation in the PK model were compared.

RESULTS

The final study population included 37 patients with SCI. The Chronic Kidney Disease Epidemiology Collaboration cystatin C equation provided significantly less bias, greater precision, and superior accuracy when used in the PK model.

CONCLUSIONS

In the SCI population, the use of Chronic Kidney Disease Epidemiology Collaboration cystatin C equation may improve initial vancomycin dosing. Further study into this potential is encouraged.

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

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

Cystatin C for early detection of acute kidney injury after laparoscopic partial nephrectomy

Introduction and Objectives:

Mortality due to AKI has not changed significantly over the past 50 years. This is due in part to failure to detect early AKI and to initiate appropriate therapeutic measures. There is therefore a need to identify biomarkers that would improve the early detection of AKI. The objective of this study was to assess whether cystatin C levels obtained at specific timepoints during laparoscopic partial nephrectomy (PN) could be early predictors of AKI.

Materials and Methods:

Twenty-five patients underwent laparoscopic PN for organ-confined tumors. All procedures were performed by two surgeons in a single institution. Plasma samples were collected preoperatively, and post-unclamping at 5, 20, 120 min and on the day following surgery. Plasma cystatin C was measured by enzyme-linked immunosorbent assay. Correlation between levels of cystatin C and other parameters of interest were assessed in order to define cystatin C ability to predict AKI and loss of renal function following laparoscopic PN.

Results:

The mean baseline eGFR was 93 ml/min/1.73 m². Warm ischemia time varied between 16 and 44 min. Post-operative day 1 (POD1) cystatin C levels compared to baseline were increased in 13 (52%) of the patients. There was a high correlation between the difference of POD 1 and baseline value, and eGFR in the immediate postoperative period (r = −0.681; P = 0.0002) and at 12-month follow-up (r = −0.460, P = 0.048). However, the variation in cystatin C levels at earlier timepoints were not associated to AKI nor renal function.

Conclusions:

High increase in POD 1 cystatin C levels from baseline may help identify patients with AKI and those at higher risk of chronic kidney disease, following laparoscopic PN.

Creatinine or cystatin C - which is a better index of renal function in morbid obesity?

PURPOSE

The most important index of renal function is estimated glomerular filtration rate (eGFR) which can be calculated from creatinine or cystatin C concentration in serum. There is uncertainty, which formula is best suited to assess renal function in morbidly obese patients. The aim of this study was to evaluate eGFR in patients with morbid obesity using formulas: Modification of Diet in Renal Disease (MDRD), Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), Grubb, Le Bricon, Hoek, Larsson, and to compare the obtained results.

MATERIAL AND METHODS

In 40 morbidly obese patients, serum concentration of cystatin C and creatinine were assayed. Values of eGFR were calculated using the above-mentioned formulas.

RESULTS

The mean value of eGFR ranged from 85.9 to 111.1 ml/min/1.73 m², depending on the formula. The biggest difference between the obtained values was 29% (Grubb vs. Hoek p<0.01). After calculation of eGFR from creatinine concentration (MDRD), 7 patients were qualified to the 2nd and 3rd stage of chronic renal disease, while application of Hoek's formula, based on cystatin C concentration, allotted 27 patients to 2nd and 3rd stage of chronic renal disease. Le Bricon formula gave eGFR values, that correlated best with albuminuria.

CONCLUSION

eGFR calculated using Le Bricon formula based on the cystatin C concentration was significantly lower than eGFR calculated from creatinine concentration and was more closely associated with albuminuria. Relying only on creatinine concentration to estimate glomerular filtration rate can lead to underestimation of renal malfunction in obese patients.

Estimated glomerular filtration rate correlates poorly with four-hour creatinine clearance in critically ill patients with acute kidney injury

Introduction. RIFLE and AKIN provide a standardised classification of acute kidney injury (AKI), but their categorical rather than continuous nature restricts their use to a research tool. A more accurate real-time description of renal function in AKI is needed, and some published data suggest that equations based on serum creatinine that estimate glomerular filtration rate (eGFR) can provide this. In addition, incorporating serum cystatin C concentration into estimates of GFR may improve their accuracy, but no eGFR equations are validated in critically ill patients with AKI. Aim. This study tests whether creatinine or cystatin-C-based eGFR equations, used in patients with CKD, offer an accurate representation of 4-hour creatinine clearance (4CrCl) in critically ill patients with AKI. Methods. Fifty-one critically ill patients with AKI were recruited. Thirty-seven met inclusion criteria, and the performance of eGFR equations was compared to 4CrCl. Results. eGFR equations were better than creatinine alone at predicting 4CrCl. Adding cystatin C to estimates did not improve the bias or add accuracy. The MDRD 7 eGFR had the best combination of correlation, bias, percentage error and accuracy. None were near acceptable standards quoted in patients with chronic kidney disease (CKD). Conclusions. eGFR equations are not sufficiently accurate for use in critically ill patients with AKI. Incorporating serum cystatin C does not improve estimates. eGFR should not be used to describe renal function in patients with AKI. Standards of accuracy for validating eGFR need to be set.

Cystatin C as a marker of glomerular filtration rate: prospects and limitations

PURPOSE OF REVIEW

There is much interest in cystatin C to replace or supplement serum creatinine to estimate the glomerular filtration rate (GFR). Here we review the performance of cystatin C and combined creatinine-cystatin C estimating equations compared to creatinine-based estimating equations in chronic and acute kidney disease.

RECENT FINDINGS

Drift in the cystatin C assay has had a large effect on the results reported using cystatin C, but these issues are not routinely considered in evaluation of GFR-estimating equations. The recently released primary reference material for cystatin C will allow less difference among assays in the future. There does not appear to be a consistent message among published studies as to whether cystatin C-based equations are better than creatinine-based equations in the general population or those with chronic kidney disease (CKD), as well as those with reduced muscle mass or chronic illness, or acute kidney injury. Cystatin C could be used in combination with creatinine as a confirmatory test for estimated GFR from creatinine.

SUMMARY

Cystatin C may have a role to estimate GFR in selected circumstances, and the next set of studies should be directed at developing implementation strategies for its use.

Earlier recognition of nephrotoxicity using novel biomarkers of acute kidney injury

CONTEXT

A broad range of drugs and chemicals are capable of evoking acute kidney injury, which is conventionally determined by rising serum creatinine concentrations. However there are important limitations to this approach, and there has been interest in alternative biomarkers that might provide a more sensitive and rapid means of detecting acute kidney injury. Most of the available clinical data have thus far been ascertained in patients requiring critical care or with acute sepsis. However, if a sensitive indicator of acute kidney injury were developed, then this could provide a significantly improved means of detecting the effects of acute drug or toxin exposure.

OBJECTIVE

To review the available data concerning potential biomarkers of acute kidney injury and to assess their relative strengths and weaknesses in comparison to existing methods based on serum creatinine concentrations. A large number of possible biomarkers have been proposed. Evidence for individual biomarkers is reviewed with a particular emphasis on those with potential application in clinical toxicology. Where available, comparative data are presented.

METHODS

There were 236 papers identified using Medline, Embase, and Google Scholar databases, of which 52 were considered directly relevant. CREATININE: Creatinine is subject to glomerular filtration and, to a lesser extent tubular secretion. Serum concentrations are an insensitive marker of acute kidney injury, and the speed of an increase from baseline depends on the magnitude of the acute injury and pre-existing kidney functional reserve. A wide range of inter-individual concentrations means that single time-point determinations are difficult to interpret, and acute kidney injury may not manifest as a detectable increase in serum creatinine concentrations until at least 24-48 h after the primary insult. KIDNEY ENZYMES: Enzymes are often localised to specific anatomical locations, and acute injury may cause a detectable increase in urinary activity due to up-regulated activity or leakage due to cell membrane disruption. Key examples include gamma-glutamyl transpeptidase (GGT), glutathione-S-transferase (GST), and N-acetyl-glucosaminidase (NAG), which are found predominantly in the proximal tubule and urinary enzyme activity increases after acute exposure to heavy metals and other nephrotoxins. NEUTROPHIL GELATINASE-ASSOCIATED LIPOCALIN: Neutrophil gelatinase-associated lipocalin (NGAL) is expressed by renal tubular epithelium, and a rise in urinary concentrations may provide an indicator of acute renal injury caused by any one of a broad range of provoking factors that is detectable before a rise in serum creatinine concentrations. CYSTATIN C: Serum and urinary cystatin C concentrations are closely related to kidney function and, for example, in acute tubular necrosis allow better prediction of the need for renal replacement therapy than serum creatinine concentrations. KIDNEY INJURY MOLECULE 1: Kidney injury molecule 1 (KIM-1) is expressed in the proximal tubule in the setting of acute ischaemia. For example, urinary KIM-1 concentrations becomes detectable within 24 h of acute tubular necrosis. Urinary KIM-1 expression may be detected after exposure to a variety of nephrotoxic agents, even when serum creatinine concentrations do not increase, and this has been accepted by regulatory authorities as a sensitive biomarker of acute kidney injury during early drug development.

CONCLUSIONS

Novel biomarkers appear capable of offering a more sensitive means of detecting acute kidney injury than existing approaches. Certain of these allow discrimination between the various mechanisms and anatomical site of acute injury. Ultimately, clinical assessment might incorporate a panel of different biomarkers, each informing on the integrated aspects of glomerular, tubular and interstitial function. Presence of biomarkers may in some cases detect mild or transient renal dysfunction that is presently undetected, and the clinical relevance needs further exploration. Whilst many potentially useful biomarkers have been proposed, comparatively few clinical data exist to support their validity in routine practice. Further prospective clinical studies are required to examine the validity of biomarkers after acute drug or toxin exposure, and to establish whether they might offer improved clinical outcomes in the setting of clinical toxicology.

Renal function in pediatric cystic fibrosis patients in the first decade of life

With increasing life expectancy and the need for lung transplantation in the cystic fibrosis (CF) population, there are increasing reports of chronic kidney disease (CKD). However, values for baseline or longitudinal glomerular filtration rate (GFR) as measured by exogenous clearance markers are lacking in this population. Retrospective cross-sectional study in 2 to 18-year-olds cared for at a single CF center who had a GFR measured by plasma disappearance of Technetium-99 m diethylenetriaminepentaacetic acid (mGFR). The primary outcome was evidence of renal dysfunction as defined by CKD stage II or below (mGFR <90 ml/min/1.73 m(2), persistent abnormalities in urinary sediment, abnormal renal imaging). Of 63 patients evaluated, four had apparent renal dysfunction, one demonstrated decreased mGFR, and three others had persistent microscopic hematuria. The mean mGFR was substantially higher (140 ± 24 ml/min/1.73 m(2)) than expected or previously reported for healthy children. We did not demonstrate the presence of significant renal impairment after limited aminoglycoside exposure in the first decade following diagnosis with CF. However, we did document the presence of glomerular hyperfiltration in a significant proportion of our CF patients.

Advances in glomerular filtration rate-estimating equations

PURPOSE OF REVIEW

Estimated glomerular filtration rate (eGFR) is now commonly reported by clinical laboratories. Here, we review the performance of current creatinine and cystatin C-based estimating equations as well as demonstration of their utility in public health and clinical practice.

RECENT FINDINGS

Lower levels of GFR are associated with multiple adverse outcomes, including acute kidney injury and medical errors. The new Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) equation improves performance and risk prediction compared with the Modification of Diet in Renal Disease study equation. Current cystatin C-based equations are not accurate in all populations, even in those with reduced muscle mass or chronic illness, in which cystatin C would be expected to outperform creatinine. eGFR reporting has led to a greater number of referrals to nephrologists, but the increased numbers do not appear to be excessive or burdensome. The Modification of Diet in Renal Disease study equation appears to be able to provide drug dosage adjustments similar to the Cockcroft-Gault equation.

SUMMARY

Estimated GFRs and their reporting can improve and facilitate clinical practice for chronic kidney disease. Understanding strengths and limitations facilitates their optimal use. Endogenous filtration markers, alone or in combination, which are less dependent on non-GFR determinants of the filtration markers, are necessary to lead to more accurate eGFRs.

Renal dysfunction in cystic fibrosis: is there cause for concern?

Most people associate cystic fibrosis (CF) with lung disease. Although this is the major cause of morbidity and mortality, CF is in fact a multi-organ disease. Patients with CF are living longer. Accompanying their increased life expectancy are complications not previously encountered. One of the less obvious concerns is that of renal dysfunction associated with long-term exposure to aminoglycosides as well as renally toxic immunosuppressants in lung transplant recipients. This article reviews what is known about the extent of the problem, summarizes what the current practices of measuring and monitoring renal function in patients with CF, and makes suggestions for alternative approaches. In particular, the potential role of cystatin C will be discussed.