The Estimation, Measurement, and Relevance of the Glomerular Filtration Rate in Stage 5 Chronic Kidney Disease

Challenges in the Care of Patients with AKI Receiving Outpatient Dialysis: AKINow Recovery Workgroup Report

BACKGROUND

Up to one third of survivors of AKI that required dialysis (AKI-D) during hospitalization remain dialysis dependent at hospital discharge. Of these, 20%-60%, depending on the clinical setting, eventually recover enough kidney function to stop dialysis, and the remainder progress to ESKD.

METHODS

To describe the challenges facing those still receiving dialysis on discharge, the AKINow Committee conducted a group discussion comprising 59 participants, including physicians, advanced practitioners, nurses, pharmacists, and patients. The discussion was framed by a patient who described gaps in care delivery at different transition points and miscommunication between care team members and the patient.

RESULTS

Group discussions collected patient perspectives of ( 1 ) being often scared and uncertain about what is happening to and around them and ( 2 ) the importance of effective and timely communication, a comfortable physical setting, and attentive and caring health care providers for a quality health care experience. Provider perspectives included ( 1 ) the recognition of the lack of evidence-based practices and quality indicators, the significant variability in current care models, and the uncertain reimbursement incentives focused on kidney recovery and ( 2 ) the urgency to address communication barriers among hospital providers and outpatient facilities.

CONCLUSIONS

The workgroup identified key areas for future research and policy change to ( 1 ) improve communication among hospital providers, dialysis units, and patients/care partners; ( 2 ) develop tools for risk classification, subphenotyping, and augmented clinical decision support; ( 3 ) improve education to providers, staff, and patients/care partners; ( 4 ) identify best practices to improve relevant outcomes; ( 5 ) validate quality indicators; and ( 6 ) assess the effect of social determinants of health on outcomes. We urge all stakeholders involved in the process of AKI-D care to align goals and work together to fill knowledge gaps and optimize the care to this highly vulnerable patient population.

Beta-trace protein as a potential biomarker of residual renal function in patients undergoing peritoneal dialysis

Background

Residual renal function is closely linked to quality of life, morbidity and mortality in dialysis patients. Beta-trace protein (BTP), a low molecular weight protein, has been suggested as marker of residual renal function, in particular in patients on hemodialysis. We hypothesized that BTP also serves as a marker of residual renal function in pertioneal dialysis patients.

Methods

In this study 34 adult patients on peritoneal dialysis were included. BTP, creatinine, cystatin C and urea concentrations were analyzed simultaneously in serum and dialysate to calculate renal and peritoneal removal of the analytes.

Results

In peritoneal dialysis patients with residual diuresis, mean serum BTP was 8.16 mg/l (SD ± 4.75 mg/l). BTP correlated inversely with residual diuresis (r_s = − 0.58, p < 0.001), residual creatinine clearance (Cl_Cr) (r_s = − 0.69, p < 0.001) and total urea clearance (Cl_urea) (r_s = − 0.56, p < 0.001). Mean peritoneal removal of BTP was 3.36 L/week/1.73m² (SD ± 1.38) and mean renal removal 15.14 L/week/1.73m² (SD ± 12.65) demonstrating a significant renal contribution to the total removal. Finally, serum BTP inversely correlated with alterations in residual diuresis (r = − 0.41, p = 0.035) and renal creatinine clearance over time (r = − 0.79, p = p < 0.001).

Conclusion

BTP measurement in the serum may be a simple tool to assess residual renal function in peritoneal dialysis patients.

Estimated glomerular filtration rate at dialysis initiation and subsequent decline in residual kidney function among incident hemodialysis patients

BACKGROUND

Higher estimated glomerular filtration rate (eGFR) at dialysis initiation, known as earlier start of dialysis, is often a surrogate of poor outcomes including higher mortality. We hypothesized that earlier dialysis initiation is associated with a faster decline in residual kidney function (RKF), which is also associated with higher mortality among incident hemodialysis (HD) patients.

METHODS

In a cohort of 4911 incident HD patients who initiated HD over a 5-year period (July 2001 to June 2006), we examined the trajectories of RKF, ascertained by renal urea clearance (KRU), over 2 years after HD initiation across strata of eGFR at HD initiation using case-mix adjusted linear mixed-effect models. We then investigated the association between annual change in RKF and mortality using Cox proportional hazard models.

RESULTS

The median (interquartile range) baseline KRU was 2.20 (1.13-3.63)  mL/min/1.73 m2. The decline of KRU was faster in patients who initiated HD at higher eGFR. The relative changes with 95% confidence intervals (CIs) in KRU at 1 year after HD initiation were -1.29 (-1.28 to -1.30), -1.17 (-1.16 to -1.18), -1.11 (-1.10 to -1.12) and -0.78 (-0.78 to -0.79)  mL/min/1.73 m2 in the eGFR categories of ≥10, 8-<10, 6-<8 and <6 mL/min/1.73 m2, respectively. The faster decline of KRU at 1 year was associated with higher all-cause mortality (reference: ≥0 mL/min/1.73 m2): hazard ratios (95% CIs) for change in KRU of -1.5 to <0, -3 to less than -1.5 and less than -3 mL/min/1.73 m2 were 1.20 (1.03-1.40), 1.42 (1.17-1.72) and 1.88 (1.47-2.40), respectively.

CONCLUSIONS

The faster decline of RKF happens with earlier dialysis initiation and is associated with higher all-cause mortality.

When to initiate dialysis for end-stage kidney disease: evidence and challenges

The decision about when to start dialysis for end-stage kidney disease (ESKD) is complex and is influenced by many factors. ESKD-related symptoms and signs are the most common indications for dialysis initiation. Creatinine-based formulae to estimate glomerular filtration rate (GFR) are inaccurate in patients with ESKD and, thus, the decision to start dialysis should not be based solely on estimated GFR (eGFR). Early dialysis initiation (ie, at an eGFR > 10 mL/min/1.73 m²) is not associated with a morbidity and mortality benefit, as shown in the Initiating Dialysis Early and Late (IDEAL) study. This observation has been incorporated into the latest guidelines, which place greater emphasis on the assessment of patients' symptoms and signs rather than eGFR. It is suggested that in asymptomatic patients with stage 5 chronic kidney disease, dialysis may be safely delayed until the eGFR is at least as low as 5-7 mL/min/1.73 m² if there is careful clinical follow-up and adequate patient education. The decision on when to start dialysis is even more challenging in older patients. Due to their comorbidities and frailty, dialysis initiation may be associated with worse outcomes and quality of life. Therefore, the decision to start dialysis in these patients should be carefully weighed against its risks, and conservative care should be considered in appropriate cases. To optimise the decision-making process for dialysis initiation, patients need to be referred to a nephrologist in a timely fashion to allow adequate pre-dialysis care and planning. Dialysis initiation and its timing should be a shared decision between physician, patients and family members, and should be tailored to the individual patient's needs.

An electronic technetium-99m-diethylenetriaminepentaacetic acid glomerular filtration rate spreadsheet with novel embedded quality assurance features

Supplemental Digital Content is available in the text.

Background

Critical clinical decisions are made on the basis of the glomerular filtration rate (GFR) measured using technetium-99m-diethylenetriaminepentaacetic acid (DTPA) administration, followed by multiple time-point plasma sampling. As GFR studies rely on few data points and produce a single result, they are prone to technical errors that may remain inconspicuous.

Objective

We describe a data analysis worksheet that provides real-time quality control (QC) indicators and evaluate our initial clinical experience.

Methods

Two hundred and forty-six consecutive GFR studies carried out at our clinics were included. Our protocol used plasma samples at 2, 3, and 4 h after injection of technetium-99m-DTPA. Duplicate plasma samples, background samples, and aliquots of an activity dilution standard were counted. Times were logged for injection and dilution standard preparation, blood sampling, and counting. Data were entered into a custom GFR analysis spreadsheet that flagged QC in real time at warning and error levels, including QC of the expected ratio between dilution standard counts–activity ratio (CARs) measurements, which was newly introduced to our clinic. The prevalence of QC events was analyzed in three phases: baseline, training, and evaluation (n=31, 69, and 146, respectively).

Results

From the baseline and training phases (n=100), CAR reference values were determined for each of two sites. In the absence of the CAR QC indicator, errors were present in 5/31 (16%) examinations, but with QC indication decreased to 7/146 (5%) (P<0.05), suggesting that the real-time QC information guided the technologists to ensure proper standard preparation and sample handling, as intended. Improvements in other QC measures were also noted, resulting in an overall error rate reduction from 23 to 8%.

Conclusion

Real-time analysis of redundant information as a component of the GFR worksheet ensures quality results, but training of technologists and interpreting physicians is essential for optimal utilization of these QC indicators.

Challenges in Measuring Glomerular Filtration Rate: A Clinical Laboratory Perspective

The assessment of kidney function is a cornerstone in the clinical management and health of the patient. Although the kidneys perform many physiologic functions and are essential for maintaining homeostasis, kidney function is typically evaluated, quantitated, and understood using the glomerular filtration rate (GFR). Although GFR can be directly measured using a variety of externally administered glomerular filtration markers, in general practice, the GFR is usually estimated (eGFR) using endogenous markers that are cleared primarily by kidney filtration. Common situations exist where the GFR needs to be measured (mGFR) in order to proceed with care. This manuscript will review laboratory challenges in the assessment of GFR. Key points to consider when implementing a mGFR testing protocol are the following: marker selection, clearance methodology (urinary vs solely plasma measurements of filtration marker), sample collection, number of samples to collect, staff required, and analytical measurement technology for the filtration marker selected. We suggest those wanting to implement mGFR testing examine site-specific institutional resources along with patient population and proceed with the approaches best suited for their clinical needs and laboratory resources available.

Influence of the CYP3A4/5 genetic score and ABCB1 polymorphisms on tacrolimus exposure and renal function in Brazilian kidney transplant patients

BACKGROUND

Polymorphisms in genes encoding transport proteins and metabolizing enzymes involved in tacrolimus (TAC) disposition may be important sources of individual variability during treatment.

OBJECTIVE

The aim of this study was to investigate the effect of combined CYP3A4 and CYP3A5 variants, using a CYP3A4/5 genetic score, and ABCB1 polymorphisms on therapeutic TAC monitoring and their relationship with clinical outcomes.

MATERIAL AND METHODS

Brazilian kidney transplant recipients (n=151), who received TAC over 3 months after transplantation, were genotyped for CYP3A4 rs2242480 (g.20230G>A), CYP3A5 rs15524 (g.31611C>T) and rs776746 (g.6986A>G), ABCB1 rs1128503 (c.1236C>T), rs1045642 (c.3435C>T), and rs2032582 (c.2677G>T/A) polymorphisms.

RESULTS

Frequencies of CYP3A4 g.20230A, CYP3A5 g.31611C, and g.6986A were 0.37, 0.26, and 0.28, respectively. These alleles were associated with TAC rapid metabolization and were used for CYP3A4/5 genetic score construction. A higher CYP3A4/5 genetic score was associated with higher TAC dose and lower concentrations for dose administered (Co/D, P<0.05). Ninety days after transplantation, the presence of two or more rapid metabolization alleles contributed toward 27.7% of Co/D variability and was associated with a lower estimated glomerular filtration rate values (P<0.05). For ABCB1, the frequencies of c.1236T, c.3435T, and c.2677T/A alleles were 0.42, 0.42, and 0.33/0.04. At 30 days after transplantation, patients carrying ABCB1 c.1236TT+c.3435TT+(c.2677TT+TA) genotypes had higher TAC Co/D than those with common or heterozygous genotypes (P<0.05).

CONCLUSION

The results show the impact of the CYP3A4/5 genetic score on TAC exposure and renal function in Brazilian patients. Furthermore, ABCB1 polymorphisms, in a combined analysis, influenced TAC Co/D at 30 days after transplantation.

Extracellular volume expansion and the preservation of residual renal function in Korean peritoneal dialysis patients: a long-term follow up study

INTRODUCTION

In chronic peritoneal dialysis patients, preservation of residual renal function (RRF) is a major determinant of patient survival, and maintaining sufficient intravascular volume has been hypothesized to be beneficial for the preservation of RRF. The present study aimed to test this hypothesis using multifrequency bioimpedence analyzer (MFBIA), in Korean peritoneal dialysis patients.

METHODS

A total of 129 patients were enrolled in this study. The baseline MFBIA was checked, and the patients were divided into the following two groups: group 1, extracellular water per total body water (ECW/TBW) < median, group 2, ECW/TBW > median. We followed up the patients, and then we analyzed the changes in the urine output (UO) and the solute clearance (weekly uKt/V) in each group. Data associated with patient and technical survivor were collected by medical chart review. The volume measurement was made using Inbody S20 equipment (Biospace, Seoul, Korea). We excluded the anuric patients at baseline.

RESULT

The median value of ECW/TBW was 0.396. The mean patient age was 49.74 ± 10.01 years, and 62.1 % of the patients were male; most of the patients were on continuous ambulatory peritoneal dialysis (89.1 %). The mean dialysis vintage was 26.20 ± 28.71 months. All of the patients were prescribed hypertensive medication, and 48.5 % of the patients had diabetes. After 25.47 ± 6.86 months of follow up, ΔUO and Δweekly Kt/V were not significantly different in the two groups as follows: ΔUO (-236.07 ± 185.15 in group 1 vs -212.21 ± 381.14 in group 2, p = 0.756); Δ weekly Kt/v (-0.23 ± 0.43 in group 1 vs -0.29 ± 0.49 in group 2, p = 0.461). The patient and technical survivor rate was inferior in the group 2, and in the multivariable analysis, initial hypervolemia was an independent factor that predicts both of the patient mortality [HR 1.001 (1.001-1.086), p = 0.047] and the technical failure [HR 1.024 (1.001-1.048), p = 0.042].

CONCLUSIONS

Extracellular volume expansion, measured by MFBIA, does not help preserve residual renal function, and is harmful for the technical and patient survival in Korean peritoneal dialysis patients.

β-Trace protein: a marker of GFR and other biological pathways

β-Trace protein (BTP), also known as lipocalin prostaglandin D2 synthase (L-PGDS; encoded by the PTGDS gene), is a low-molecular-weight glycoprotein and an emerging novel marker of glomerular filtration rate. BTP is an important constituent of cerebral spinal fluid and is found in much lower concentrations in blood. Its serum origin and renal handling remain poorly understood. Unlike serum creatinine, BTP is not physiologically inert. It possesses both ligand-binding and enzymatic properties. BTP catalyzes the conversion of prostaglandin H2 (PGH2) to PGD2. PGD2 is an eicosanoid involved in a variety of important physiologic processes, including platelet aggregation, vasodilation, inflammation, adipogenesis, and bone remodeling. Several studies now have documented BTP's strong association with glomerular filtration rate, end-stage renal disease, cardiovascular disease, and death in a variety of different patient populations. This review provides an overview of the biochemistry, physiology and metabolism, biological functions, and measurement of BTP; summarizes the evidence for BTP as a marker of both kidney function and cardiovascular disease; and then considers the interplay between its biological properties, serum concentration, and patient outcomes.

Urea nitrogen, creatinine, and uric acid levels in postmortem serum, vitreous humor, and pericardial fluid

Urea nitrogen, creatinine, and uric acid are relatively stable in postmortem serum and may, therefore, be used for diagnostic purposes when chronic kidney disease and end-stage renal failure are investigated as causes of death. Nevertheless, uncertainties remain in defining the best alternative to postmortem serum for the identification and assessment of significantly decreased kidney function. In this study, we investigated urea nitrogen, creatinine, and uric acid levels in postmortem serum, pericardial fluid, and vitreous humor in a series of medico-legal cases (500 autopsies) with various causes of death. No postmortem interval-related differences were observed in any of the investigated fluids for any analyzed parameter, confirming the biochemical stability of all compounds after death. Data analysis failed to reveal statistically significant differences between postmortem serum and pericardial fluid urea nitrogen, creatinine, and uric acid concentrations. Conversely, statistically significant differences were observed in all analyzed biomarkers between postmortem serum and vitreous humor levels, with lower concentrations of all markers measured in vitreous. The results of this study suggest that, in order to estimate as accurately as possible blood analyte concentrations at the time of death, pericardial fluid should be preferred to vitreous humor.

Association between GFR estimated by multiple methods at dialysis commencement and patient survival

BACKGROUND AND OBJECTIVES

The Initiating Dialysis Early and Late study showed that planned early or late initiation of dialysis, based on the Cockcroft and Gault estimation of GFR, was associated with identical clinical outcomes. This study examined the association of all-cause mortality with estimated GFR at dialysis commencement, which was determined using multiple formulas.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Initiating Dialysis Early and Late trial participants were stratified into tertiles according to the estimated GFR measured by Cockcroft and Gault, Modification of Diet in Renal Disease, or Chronic Kidney Disease-Epidemiology Collaboration formula at dialysis commencement. Patient survival was determined using multivariable Cox proportional hazards model regression.

RESULTS

Only Initiating Dialysis Early and Late trial participants who commenced on dialysis were included in this study (n=768). A total of 275 patients died during the study. After adjustment for age, sex, racial origin, body mass index, diabetes, and cardiovascular disease, no significant differences in survival were observed between estimated GFR tertiles determined by Cockcroft and Gault (lowest tertile adjusted hazard ratio, 1.11; 95% confidence interval, 0.82 to 1.49; middle tertile hazard ratio, 1.29; 95% confidence interval, 0.96 to 1.74; highest tertile reference), Modification of Diet in Renal Disease (lowest tertile hazard ratio, 0.88; 95% confidence interval, 0.63 to 1.24; middle tertile hazard ratio, 1.20; 95% confidence interval, 0.90 to 1.61; highest tertile reference), and Chronic Kidney Disease-Epidemiology Collaboration equations (lowest tertile hazard ratio, 0.93; 95% confidence interval, 0.67 to 1.27; middle tertile hazard ratio, 1.15; 95% confidence interval, 0.86 to 1.54; highest tertile reference).

CONCLUSION

Estimated GFR at dialysis commencement was not significantly associated with patient survival, regardless of the formula used. However, a clinically important association cannot be excluded, because observed confidence intervals were wide.

Predicting residual renal function in peritoneal dialysis patients using an estimated glomerular filtration rate based on serum creatinine levels

BACKGROUND

The aim of this study was to evaluate regression equations correcting estimated glomerular filtration rate (eGFR) and the clinical significance of the corrected eGFRs calculated using these equations.

PATIENTS AND METHODS

The authors determined how well corrected eGFR values calculated using regression equations predict residual renal function (RRF).

RESULTS

RRF values were correlated with all eGFR values of nonanuric patients of both genders. Peritoneal creatinine clearance values were not correlated with eGFRs in anuric patients of either gender. In males, eGFR biases ranged from -5.66 to -3.25, and in females, from -5.96 to -3.21. However, these biases decreased when eGFR values were transformed to corrected eGFR values. The area under the curve of the corrected eGFR values was acceptable for a diagnosis of RRF loss.

CONCLUSION

Corrected eGFR values obtained using these methods may provide an alternative means of predicting RRF without 24-hour urine collection.

Extracellular volume expansion, measured by multifrequency bioimpedance, does not help preserve residual renal function in peritoneal dialysis patients

Residual renal function is a major survival determinant for peritoneal dialysis patients. Hypovolemia can cause acute kidney injury and loss of residual renal function, and it has been suggested that patients receiving peritoneal dialysis should preferably be maintained hypervolemic to preserve residual renal function. Here we determined whether hydration status predicted long-term changes in residual renal function. Changes in residual renal function and extracellular water (ECW) to total body water (TBW) measured by multifrequency bioimpedance in 237 adult patients who had paired baseline and serial 12 monthly measurements were examined. Baseline hydration status (ECW/TBW) was not significantly associated with preservation of residual renal function, unlike baseline and follow-up mean arterial blood pressure. When the cohort was split into tertiles according to baseline hydration status, there was no significant correlation seen between change in hydration status and subsequent loss in residual renal function. Increased ECW/TBW in peritoneal dialysis patients was not associated with preservation of residual renal function. Similarly, increments and decrements in ECW/TBW were not associated with preservation or reduction in residual renal function. Thus, our study does not support the view that overhydration preserves residual renal function and such a policy risks the consequences of persistent hypervolemia.

Chronic kidney disease epidemiology collaboration equation accuracy in predicting peritoneal dialysis-delivered creatinine clearance

INTRODUCTION

Measuring total (residual kidney plus peritoneal) creatinine clearance (CrCl) with 24-h urine and dialysate collections is recommended for peritoneal dialysis (PD) adequacy evaluation. Prediction equations applied in this instance could simplify the approach. Cockcroft-Gault and modification of diet in renal disease (MDRD) four (MDRD-4) and six (MDRD-6) variables equations have been tested in this setting, and conflicting results have been reported. The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation is currently considered to be more sensitive than the established equations for kidney function estimation. However, its performance in PD adequacy evaluation has not been studied. Our aim was to assess CKD-EPI equation's performance in predicting total measured CrCl (MCC) in PD patients.

MATERIAL AND METHODS

A group of 23 consecutive PD patients, male/female: 5/18, median age: 66 (32-91) years, median time on PD 32 (2-126) months, were enrolled in the study. All were treated by automated PD (APD). Sixteen out of twenty-three had residual renal function (RRF). MCC was determined from 24-h dialysate and urine collections and also predicted by Cockcroft-Gault, MDRD (4 and 6), and CKD-EPI equations.

RESULTS

CKD-EPI and MDRD-6 estimation results were similar to MCC (9.01 ± 3.90 and 9.54 ± 2.98 vs. 8.64 ± 3.75 mL/min/1.73 m(2) p = 0.49 and 0.09, respectively). Neither the presence nor the volume of residual urine affected the accuracy of prediction. Cockcroft-Gault and MDRD-4 equations differed significantly from MCC and were not accurately predictive.

CONCLUSION

CKD-EPI equation could be used with accuracy for predicting MCC in PD patients. Only MDRD-6 showed similar accuracy, whereas MDRD-4 and Cockcroft-Gault equations were found to be inappropriate in this setting.

When should we commence dialysis? The story of a lingering problem and today's scene after the IDEAL study

Over the last 15-20 years, there has been an increasing trend for dialysis to be commenced earlier in the development of chronic kidney disease (CKD). The drivers for initiation of dialysis at higher levels of renal function are complex but were primarily based on the assumption that by improving solute and water clearances with earlier dialysis, morbidity, mortality and quality of life would be improved. The Initiating Dialysis Early and Late (IDEAL) trial definitively demonstrated that elective earlier initiation of dialysis was not associated with improved clinical outcomes or quality of life. Indeed, no subset of patients was found to benefit from earlier dialysis. Observational data suggests that patients who commence dialysis with higher levels of renal function are more likely to have significant comorbidity that results in higher mortality rates compared to patients who remain clinically well and biochemically stable and are able to defer the initiation of dialysis till later in the course of CKD. However, patients who are able to defer dialysis should have appropriate access created so as to avoid the use of temporary catheters and to facilitate initiation using the preferred dialysis modality. Estimates of glomerular filtration rates in Stage 5 CKD have been poorly validated and should not be used as the key determinant influencing the commencement of dialysis. The results of the IDEAL trial have influenced guidelines internationally and provide clinicians, patients and health care providers with important information to drive clinical decision making and rational service planning.