Social determinants of health and dialysis modality selection in patients with advanced chronic kidney disease: A retrospective cohort study

BACKGROUND

Social determinants of health are non-medical factors that impact health. For patients with chronic kidney disease (CKD) progressing to kidney failure, the influence of social determinants of health on dialysis modality selection (haemodialysis vs. peritoneal dialysis (PD)) is incompletely understood.

METHODS

Retrospective cohort study of 981 consecutive patients with advanced CKD referred to the Ottawa Hospital Multi-Care Kidney Clinic (Canada) who progressed to dialysis from 2010 to 2021. Multivariable logistic regression was used to measure odds ratios (OR) for the associations between social determinants of health (education, employment, marital status and residence) and modality of dialysis initiation.

RESULTS

The mean age and estimated glomerular filtration rate were 64 and 18 mL/min/1.73 m2, respectively. Not having a high school degree was associated with lower odds of initiating dialysis via PD compared to having a college degree (29% vs. 48%, OR 0.55 (95% confidence interval (CI) 0.34-0.88)). Unemployment was associated with lower odds of initiating dialysis via PD compared to active employment (38% vs. 62%, OR 0.40 (95% CI 0.27-0.60)). Being single was associated with lower odds of initiating dialysis via PD compared to being married (35% vs. 48%, adjusted OR 0.52 (95% CI 0.39-0.70)). Living alone at home was associated with lower odds of initiating dialysis via PD compared to living at home with family (33% vs. 47%, adjusted OR 0.55 (95% CI 0.39-0.78)).

CONCLUSIONS

Social determinants of health including education, employment, marital status and residence are associated with dialysis modality selection. Addressing these 'upstream' social factors may allow for more equitable outcomes during the transition from advanced CKD to kidney failure.

Serum total testosterone is associated with phosphate and calcium excretion in response to oral phosphate loading in healthy middle-aged males

Androgen receptors are expressed in the kidney and serum testosterone is negatively associated with serum phosphate in males, suggesting a role of testosterone in renal phosphate handling. In this cross-sectional study, we examined the association of serum total and free testosterone with acute phosphate and calcium excretion in males in response to an oral phosphate challenge. Thirty-five healthy adult males with normal baseline testosterone levels consumed a 500 mg phosphorus drink and the urinary excretion of minerals, as well as levels of relevant circulating parameters, were assessed at baseline and hourly for 4 h. Serum total testosterone was positively associated with overall phosphate excretion (r = 0.35, p = 0.04) and calcium excretion (r = 0.44, p = 0.00) in response to the challenge. Serum free testosterone was positively associated with post-challenge calcium excretion (r = 0.34, p = 0.048), but significance was not reached for phosphate excretion (r = 0.31, p = 0.07). Serum total and free testosterone were not associated with parathyroid hormone, fibroblast growth factor-23, or vitamin D-key factors implicated in phosphate and calcium regulation. Overall, higher serum total testosterone levels in healthy middle-aged males are associated with a greater capacity to acutely excrete phosphate and calcium after a single oral phosphate challenge, suggesting potential ramifications of testosterone deficiency related to mineral homeostasis.

Short Timeframe Prediction of Kidney Failure among Patients with Advanced Chronic Kidney Disease

BACKGROUND

Development of a short timeframe (6-12 months) kidney failure risk prediction model may serve to improve transitions from advanced chronic kidney disease (CKD) to kidney failure and reduce rates of unplanned dialysis. The optimal model for short timeframe kidney failure risk prediction remains unknown.

METHODS

This retrospective study included 1757 consecutive patients with advanced CKD (mean age 66 years, estimated glomerular filtration rate 18 mL/min/1.73 m2). We compared the performance of Cox regression models using (a) baseline variables alone, (b) time-varying variables and machine learning models, (c) random survival forest, (d) random forest classifier in the prediction of kidney failure over 6/12/24 months. Performance metrics included area under the receiver operating characteristic curve (AUC-ROC) and maximum precision at 70% recall (PrRe70). Top-performing models were applied to 2 independent external cohorts.

RESULTS

Compared to the baseline Cox model, the machine learning and time-varying Cox models demonstrated higher 6-month performance [Cox baseline: AUC-ROC 0.85 (95% CI 0.84-0.86), PrRe70 0.53 (95% CI 0.51-0.55); Cox time-varying: AUC-ROC 0.88 (95% CI 0.87-0.89), PrRe70 0.62 (95% CI 0.60-0.64); random survival forest: AUC-ROC 0.87 (95% CI 0.86-0.88), PrRe70 0.61 (95% CI 0.57-0.64); random forest classifier AUC-ROC 0.88 (95% CI 0.87-0.89), PrRe70 0.62 (95% CI 0.59-0.65)]. These trends persisted, but were less pronounced, at 12 months. The random forest classifier was the highest performing model at 6 and 12 months. At 24 months, all models performed similarly. Model performance did not significantly degrade upon external validation.

CONCLUSIONS

When predicting kidney failure over short timeframes among patients with advanced CKD, machine learning incorporating time-updated data provides enhanced performance compared with traditional Cox models.

Sex Differences in Phosphate Homeostasis: Females Excrete More Phosphate and Calcium After an Oral Phosphate Challenge

CONTEXT

Dietary consumption of phosphate is increasing, and elevated serum phosphate is associated with increased cardiovascular disease (CVD) risk. Sex differences in phosphate homeostasis and response to changes in dietary phosphate intake, which are not captured by clinically measured analytes, may contribute to differences in CVD presentation and bone disease.

OBJECTIVE

To assess sex differences in acute phosphate homeostasis in response to a single oral phosphate challenge.

DESIGN

Cross-sectional.

SETTING

General community.

PARTICIPANTS

78 participants (40-76 years) with measured glomerular filtration rate >60 mL/min/1.73 m2 and no clinically diagnosed CVD and 14 young healthy adults.

MAIN OUTCOME MEASURES

To elucidate subtle alterations in phosphate homeostasis, we employ an acute challenge whereby the hormonal response, circulating mineral levels, and urinary excretion are assessed following an oral challenge of phosphate.

RESULTS

Although both males and females had similar changes in circulating phosphate, calcium, and parathyroid hormone in response to the challenge, females excreted ∼1.9x more phosphate and ∼2.7x more calcium than males, despite not consuming calcium. These sex differences were recapitulated in healthy young adults. This excretion response did not correlate to age, serum phosphate, or estradiol levels. The females with greater excretion of phosphate had higher levels of bone resorption markers compared to formation markers.

CONCLUSIONS

Taken together, these data identify sex differences in acute phosphate homeostasis, specifically that females may mobilize and excrete endogenous sources of calcium and phosphate in response to oral phosphate compared to males. While high levels of dietary phosphate negatively impact bone, our results suggest that females may incur more risk from these diets.

The 1,24,25(OH)3D3 metabolite in clinical and experimental CKD: Impact of calcitriol treatment

Calcitriol, and other vitamin D receptor activators, remain a primary treatment for elevated parathyroid hormone levels in patients with end stage kidney disease. The objective of this study was to assess the 24-hydroxylation-mediated metabolism of 25(OH)D₃ and 1,25(OH)₂D₃ in rats with experimental kidney disease treated with calcitriol and in a cross-sectional analysis of patients requiring hemodialysis. Methods: Animals were stratified by creatinine into a time control group or calcitriol (20 ng/kg/day) for 3 weeks following CKD induction using a dietary adenine model (0.25% adenine). Hemodialysis patients were recruited and demographic data including calcitriol prescription was obtained by chart review and participant interview. Vitamin D metabolites were assessed using LC-MS/MS. In the rat model, 1,25(OH)₂D₃ levels increased substantially in calcitriol-treated rats yet there was no increase in its primary metabolite: 1,24,25(OH)₂D₃. A lower ratio of 1,24,25(OH)₂D₃:1,25(OH)₂D₃ (1,25-VMR) was associated with increased calcium levels in calcitriol treated rats. In hemodialysis patients (N = 86), the level of 1,25(OH)₂D₃ was substantially higher in calcitriol-treated patients yet there was no difference between groups in 1,24,25(OH)₃D₃, resulting in a marked decrease in the 1,25-VMR in calcitriol treated patients. In hemodialysis patients treated with calcitriol, 1,25(OH)₂D₃ and a lower ratio between 1,24,25(OH)₃D₃ and 1,25(OH)₂D₃ were associated with higher serum calcium levels. Impaired metabolism of exogenous calcitriol may contribute to the adverse effects associated with this treatment. A better understanding of the uniquely dysfunctional catabolic vitamin D profile in CKD may guide more effective treatment strategies.

Rituximab Chimeric Anti-CD20 Monoclonal Antibody Therapy for Relapsed Indolent Lymphoma: Half of Patients Respond to a Four-Dose Treatment Program

PURPOSE

The CD20 antigen is expressed on more than 90% of B-cell lymphomas. It is appealing for targeted therapy, because it does not shed or modulate. A chimeric monoclonal antibody more effectively mediates host effector functions and is itself less immunogenic than are murine antibodies.

PATIENTS AND METHODS

This was a multiinstitutional trial of the chimeric anti-CD20 antibody, IDEC-C2B8. Patients with relapsed low grade or follicular lymphoma received an outpatient treatment course of IDEC-C2B8 375 mg/m2 intravenously weekly for four doses.

RESULTS

From 31 centers, 166 patients were entered. Of this intent-to-treat group, 48% responded. With a median follow-up duration of 11.8 months, the projected median time to progression for responders is 13.0 months. Serum antibody levels were sustained longer after the fourth infusion than after the first, and were higher in responders and in patients with lower tumor burden. The majority of adverse events occurred during the first infusion and were grade 1 or 2; fever and chills were the most common events. Only 12% of patients had grade 3 and 3% grade 4 toxicities. A human antichimeric antibody was detected in only one patient.

CONCLUSION

The response rate of 48% with IDEC-C2B8 is comparable to results with single-agent cytotoxic chemotherapy. Toxicity was mild. Attention needs to be paid to the rate of antibody infusion, with titration according to toxicity. Further investigation of this agent is warranted, including its use in conjunction with standard chemotherapy.

Performance of the 2021 Race-Free CKD-EPI Creatinine- and Cystatin C-Based Estimated GFR Equations Among Kidney Transplant Recipients

RATIONALE & OBJECTIVE

Race-free estimated glomerular filtration rate (eGFR) equations incorporating creatinine with and without cystatin C were recently developed and recommended for routine use. However, the performance of these equations among kidney transplant recipients (KTRs) remains unknown.

STUDY DESIGN

Cross-sectional study to validate the 2021 race-free Chronic Kidney Disease (CKD) Epidemiology Collaboration (CKD-EPI) eGFR equation based on creatinine alone (eGFR_cr) or based on creatinine and cystatin C (eGFR_cr-cys) among KTRs.

SETTING & PARTICIPANTS

KTRs in stable condition (N = 415) from Canada and New Zealand with same-day measurements of creatinine, cystatin C, and glomerular filtration rate (GFR) using radiolabeled diethylenetriaminepentaacetic acid.

TESTS COMPARED

The 2009 CKD-EPI eGFR_cr, 2021 CKD-EPI eGFR_cr, 2012 CKD-EPI eGFR_cr-cys, 2021 CKD-EPI eGFR_cr-cys, 2012 CKD-EPI eGFR_cys, and Modification of Diet in Renal Disease (MDRD) Study eGFR equations were compared with measured GFR.

OUTCOMES

Bias, precision, accuracy, and correct classification by CKD stage. Bias was defined as the difference between estimated and measured GFR. Precision was represented by the interquartile range. Accuracy was defined as the percentages of participants with eGFRs within 10%/20%/30% (P₁₀/P₂₀/P₃₀) of measured GFR, root mean square error, and mean absolute error.

RESULTS

87% of patients studied were White, 3% Black, and 10% other races. Mean measured GFR was 53 ± 19 (SD) mL/min/1.73 m². The 2009 and 2021 CKD-EPI eGFR_cr equations demonstrated similar median bias (-2.3 vs -0.2 mL/min/1.73 m², respectively), precision (14.5 vs 14.9 mL/min/1.73 m²), and accuracy (P₁₀/P₂₀/P₃₀, 32%/65%/84% vs 33%/63%/84%). The 2012 and 2021 CKD-EPI eGFR_cr-cys equations also demonstrated similar median bias (-3.6 vs 0.3 mL/min/1.73 m², respectively), precision (13.3 vs 14.3 mL/min/1.73 m²), and accuracy (P₁₀/P₂₀/P₃₀, 32%/63%/80% vs 32%/67%/83%). No clear difference in performance was detected between the 2021 CKD-EPI eGFR_cr and eGFR_cr-cys equations among KTRs. The proportion of correct classification by CKD stage was similar across all eGFR equations.

LIMITATIONS

Moderate sample size, few patients had a GFR <30 mL/min/1.73 m², and the large majority of patients were White.

CONCLUSIONS

Among KTRs, the 2021 race-free CKD-EPI eGFR equations perform similarly to the previous CKD-EPI equations that included race correction terms. No significant difference in performance was observed between the 2021 CKD-EPI eGFR_cr and eGFR_cr-cys equations in the kidney transplant population.

Twice versus thrice weekly hemodialysis: A systematic review

INTRODUCTION

Thrice weekly hemodialysis (HD) is currently the norm in high income countries but there is mounting interest in twice weekly HD in certain settings. We performed this systematic review to summarize the available evidence comparing twice to thrice weekly HD.

METHODS

A systematic literature search was performed in Ovid MEDLINE, Ovid Embase, and the Cochrane Central Register of Controlled Trials to identify cohort and randomized controlled trials evaluating outcomes of twice versus thrice weekly HD. The bibliographies of identified studies were hand searched to find any additional studies. Risk of bias was assessed using the Newcastle-Ottawa scale for observational studies.

FINDINGS

No randomized controlled trials and 21 cohort studies were identified. Overall study quality was modest with high risk of selection bias and inadequate controlling for confounders. The most commonly evaluated outcome measures were survival and residual kidney function. No studies assessed quality of life. Study results were variable and there was no clear signal for overwhelming risk or benefit of twice versus thrice weekly HD with the exception of residual kidney function which consistently showed slower decline in the twice weekly group.

DISCUSSION

There is a paucity of high quality data comparing the risks and benefits of twice vs thrice weekly HD. Randomized controlled trial evidence is required to inform clinicians and HD prescription guidelines.

Composition and functionality of bacterioplankton communities in marine coastal zones adjacent to finfish aquaculture

Finfish aquaculture is a fast-growing primary industry and is increasingly common in coastal ecosystems. Bacterioplankton is ubiquitous in marine environment and respond rapidly to environmental changes. Changes in bacterioplankton community are not well understood in semi-enclosed stratified embayments. This study aims to examine aquaculture effects in the composition and functional profiles of the bacterioplankton community using amplicon sequencing along a distance gradient from two finfish leases in a marine embayment. Results revealed natural stratification in bacterioplankton associated to NOx, conductivity, salinity, temperature and PO₄. Among the differentially abundant bacteria in leases, we found members associated with nutrient enrichment and aquaculture activities. Abundant predicted functions near leases were assigned to organic matter degradation, fermentation, and antibiotic resistance. This study provides a first effort to describe changes in the bacterioplankton community composition and function due to finfish aquaculture in a semi-enclosed and highly stratified embayment with a significant freshwater input.

Death and Dialysis Following Discharge From Chronic Kidney Disease Clinic: A Retrospective Cohort Study

Background:

Multidisciplinary care is recommended for patients with advanced chronic kidney disease (CKD). A formalized, risk-based approach to CKD management is being adopted in some jurisdictions. In Ontario, Canada, the eligibility criteria for multidisciplinary CKD care funding were revised between 2016 and 2018 to a 2 year risk of kidney replacement therapy (KRT) greater than 10% calculated by the 4-variable Kidney Failure Risk Equation (KFRE). Implementation of the risk-based approach has led to the discharge of prevalent CKD patients.

Objective:

The primary objective of this study was to determine the frequency of occurrence of death and KRT initiation in patients discharged from CKD clinic.

Design:

Retrospective cohort study

Setting:

Single center multidisciplinary CKD clinic in Ontario, Canada

Patients:

Four hundred and twenty five patients seen at least once in 2013 at the multidisciplinary CKD clinic

Measurements:

Outcomes included discharge status, death, re-referral and KRT initiation. Reasons for discharge were recorded.

Methods:

Outcomes were extracted from available electronic medical records and the provincial death registry between the patient’s initial clinic visit in 2013 and January 1, 2020. KFRE-2 scores were calculated using the 4-variable KFRE equation. The hazard rates of death and KRT after discharge due to stable eGFR/low KFRE were compared to patients who remained in the clinic.

Results:

Of the 425 CKD patients, 69 (16%) and 19 (4%) were discharged to primary care and general nephrology, respectively. Of those discharged, 7 (8%) were re-referred to nephrology or CKD clinic, while only 2 (2%) discharged patients required subsequent KRT. The hazard of mortality was reduced after discharge from the clinic due to stable eGFR/low KFRE (adjusted HR = 0.45 [95% CI, 0.25-0.78, P = .005]).

Limitations:

Single center, observational retrospective study design and unknown kidney function over time post discharge for most patients

Conclusions:

Discharge of low risk patients from multidisciplinary CKD clinic appears feasible and safe, with fewer than 1 in 40 discharged patients subsequently initiated on KRT over the following 7 years.

Can Peer Review Be Kinder? Supportive Peer Review: A Re-Commitment to Kindness and a Call to Action

Peer review aims to select articles for publication and to improve articles before publication. We believe that this process can be infused by kindness without losing rigor. In 2014, the founding editorial team of the Canadian Journal of Kidney Health and Disease (CJKHD) made an explicit commitment to treat authors as we would wish to be treated ourselves. This broader group of authors reaffirms this principle, for which we suggest the terminology “supportive review.”

Independent External Validation and Comparison of Death and Kidney Replacement Therapy Prediction Models in Advanced CKD

Rationale & Objective

Study Design

Setting & Participants

Outcomes & Analytical Approach

Results

Limitations

Conclusions

Evaluation of novel glomerular filtration rate estimation equations in adolescents and young adults with type 1 diabetes

AIMS

Individuals with type 1 diabetes (T1D) are at an increased risk of chronic kidney disease making estimation of glomerular filtration rate (eGFR) an important component of diabetes care. Which eGFR equation is most appropriate to use in patients with T1D during the transition to adult care is unclear. We, therefore, sought to evaluate the performance of five eGFR equations in adolescents and young adults with T1D.

METHODS

Measured iohexol-based glomerular filtration rate was compared to the Chronic Kidney Disease and Epidemiology Collaboration (CKD-EPI) eGFR, Chronic Kidney Disease in Children (CKiD) eGFR, and three recently developed age-adjusted versions of these in 53 patients with T1D and preserved GFR using bias, precision, and accuracy.

RESULTS

The best performance was found in the sex-dependent CKiD equation (bias: -0.8, accuracy: 11.8 ml/min/1.73 m²). Bias and accuracy (26.4 and 26.8 ml/min/1.73 m²) were worst in the CKD-EPI equation. Age-dependent adjustment improved performance for this equation (bias: 5.3, accuracy: 13.4 ml/min/1.73 m²), but not for the CKiD equation (bias: 15.5, accuracy: 18.8 ml/min/1.73 m²).

CONCLUSION

Age-adjustment improved performance for the CKD-EPI equation, but not for the CKiD equation. The sex-adjusted CKiD equation performed best out of all equations.

Structure-Guided Development of Potent Benzoylurea Inhibitors of BCL-XL and BCL-2

The BCL-2 family of proteins (including the prosurvival proteins BCL-2, BCL-X_L, and MCL-1) is an important target for the development of novel anticancer therapeutics. Despite the challenges of targeting protein-protein interaction (PPI) interfaces with small molecules, a number of inhibitors (called BH3 mimetics) have entered the clinic and the BCL-2 inhibitor, ABT-199/venetoclax, is already proving transformative. For BCL-X_L, new validated chemical series are desirable. Here, we outline the crystallography-guided development of a structurally distinct series of BCL-X_L/BCL-2 inhibitors based on a benzoylurea scaffold, originally proposed as α-helix mimetics. We describe structure-guided exploration of a cryptic "p5" pocket identified in BCL-X_L. This work yields novel inhibitors with submicromolar binding, with marked selectivity toward BCL-X_L. Extension into the hydrophobic p2 pocket yielded the most potent inhibitor in the series, binding strongly to BCL-X_L and BCL-2 (nanomolar-range half-maximal inhibitory concentration (IC₅₀)) and displaying mechanism-based killing in cells engineered to depend on BCL-X_L for survival.

Parathyroid hormone measurement in chronic kidney disease: Impact of inter-method variability on mineral bone disease assessment

BACKGROUND

Parathyroid hormone (PTH) is measured routinely as part of Chronic Kidney Disease Bone and Mineral Disorders (CKD-MBD) assessment. Multiple PTH assays exist with known differences resulting in CKD-MBD guidelines recommending treatment based on assay-specific thresholds. The study objectives are to assess between manufacturer and within manufacturer variability of PTH assays and the impact of assay variability on the assessment of CKD-BMD using both vendor defined and empirically derived thresholds.

METHODS

Data were collected from Ontario, Canada's Proficiency Testing Program (24 challenge vials, 115-133 laboratories all using secondary generation PTH assays. Mean PTH and precision by the coefficient of analytical variation (CV_a) were calculated. For each vial, whether the manufacturer's mean value exceeded the vendor-defined and empirically-derived upper limit of normal (ULN) was recorded and the concordance between assays was determined.

RESULTS

Across all laboratories, the mean PTH range was 12.0 ± 3.9 pmol/L and the mean CV_a was 30%. The percent of vials with a mean PTH exceeding manufacturer's specific ULN varied substantially between manufacturers. Only 58% of vials had complete concordance as to whether mean PTH was above assay-specific ULNs. This increased to 83% using the empirically derived ULN.

CONCLUSIONS

CKD-BMD assessment and management will depend on the PTH assay. The between-assay variability is reduced but not eliminated when empirically derived reference intervals are used. Improvements in PTH measurement are required in order to ensure consistent patient care.

Secreted Phosphoprotein 24 is a Biomarker of Mineral Metabolism

The 24 kD form of secreted phosphoprotein (SPP-24), a cytokine-binding bone matrix protein with various truncated C-terminal products, is primarily synthesized by the liver. SPP-24 shares homology with fetuin-A, a potent vascular and soft tissue calcification inhibitor and SPP-24 is one component of calciprotein particles (CPPs), a circulating fetuin-mineral complex. The limited molecular evidence to date suggests that SPP-24 may also function as an inhibitor of bone formation and ectopic vascular calcification, potentially through bone morphogenic protein 2 (BMP-2) and Wnt-signaling mediated actions. The C-terminal products of SPP-24 bind to BMP-2 and attenuate BMP-2-induced bone formation. The aim of this study was to assess circulating SPP-24 in relation to kidney function and in concert with markers of mineral metabolism in humans. SPP-24 was measured in the serum of total of 192 subjects using ELISA-based measurements. Subjects were participants of one of two cohorts: (1) mGFR Cohort (n = 80) was participants of a study of measured GFR (mGFR) using inulin urinary clearance, recruited mostly from a chronic kidney disease clinic with low-range kidney function (eGFR 38.7 ± 25.0 mL/min/1.73 m²) and (2) CaMOS Cohort (n = 112) was a subset of randomly selected, community-dwelling participants of year 10 of the Canadian Multicentre Osteoporosis Study with eGFR in the normal range of 75.0 ± 15.9 mL/min/1.73 m². In the combined cohort, the mean SPP-24 was 167.7 ± 101.1 ng/mL (range 33.4-633.6 ng/mL). The mean age was 66.5 ± 11.3, 57.1% female and mean eGFR (CKD-EPI) was 59.9 ± 27.0 mL/min/1.73 m² (range 8-122 mL/min/1.73 m²). There was a strong inverse correlation between SPP-24 and eGFR (R = - 0.58, p < 0.001) that remained after adjustment for age. Following adjustment for age, eGFR, and sex, SPP-24 was significantly associated with phosphate (R = - 0.199), PTH (R = 0.298), and the Wnt-signaling inhibitor Dickkopf-related protein 1 (R = - 0.156). The results of this study indicate that SPP-24 is significantly altered by kidney function and is the first human data linking levels of SPP-24 to other biomarkers involved in mineral metabolism. Whether there is a role for circulating SPP-24 in bone formation and ectopic mineralization requires further study.

Circulating Levels of Dickkopf-Related Protein 1 Decrease as Measured GFR Declines and Are Associated with PTH Levels

BACKGROUND

The Wnt/β-catenin pathway has been implicated in the development of adynamic bone disease in early-stage chronic kidney disease (CKD). Dickkopf-related protein 1 (DKK1) and sclerostin are antagonists of the Wnt/β-catenin pathway yet have not been widely used as clinical indicators of bone disease. This study characterized levels of DKK1, sclerostin, and other biomarkers of mineral metabolism in participants across a spectrum of inulin-measured glomerular filtration rate (GFR).

METHODS

GFR was measured by urinary inulin clearance (mGFR) in 90 participants. Blood samples were obtained for measurement of circulating DKK1, sclerostin, fibroblast growth factor 23 (FGF-23), parathyroid hormone (PTH), calcium, phosphate, α-klotho, and vitamin D metabolites including 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3. Spearman correlations and linear regressions were used where appropriate to examine the associations between measured values.

RESULTS

The median [IQR] age was 64 years [53.0-71.0], and the median [IQR] mGFR was 32.6 [21.7-60.6] mL/min. DKK1 decreased (r = 0.6, p < 0.001) and sclerostin increased (r = -0.4, p < 0.001) as kidney function declined, and both were associated with phosphate, PTH, FGF-23, and 1,25-dihydroxyvitamin D3 in the unadjusted analysis. After adjustment for age and mGFR, DKK1 remained significantly associated with PTH.

CONCLUSION

The results of this study demonstrate opposing trends in Wnt/β-catenin pathway inhibitors, DKK1 and sclerostin, as mGFR declines. Unlike sclerostin, DKK1 levels decreased significantly as mGFR declined and was independently associated with PTH. Future studies should determine whether measurement of Wnt signaling inhibitors may be useful in predicting bone histomorphometric findings and important clinical outcomes in patients with CKD.

Performance of the Kidney Failure Risk Equation by Disease Etiology in Advanced CKD

BACKGROUND AND OBJECTIVES

The kidney failure risk equation is a clinical tool commonly used for prediction of progression from CKD to kidney failure. The kidney failure risk equation's accuracy in advanced CKD and whether this varies by CKD etiology remains unknown. This study examined the kidney failure risk equation's discrimination and calibration at 2 and 5 years among a large tertiary care population with advanced CKD from heterogeneous etiologies.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This retrospective cohort study included 1293 patients with advanced CKD (median eGFR 15 ml/min per 1.73 m²) referred to the Ottawa Hospital Multi-Care Kidney Clinic between 2010 and 2016, with follow-up clinical data available through 2018. Four-variable kidney failure risk equation scores for 2- and 5-year risks of progression to kidney failure (defined as dialysis or kidney transplantation) were calculated upon initial referral and correlated with the subsequent observed kidney failure incidence within these time frames. Receiver operating characteristic curves and calibration plots were used to measure the discrimination and calibration of the kidney failure risk equation both in the overall advanced CKD population and by CKD etiology: diabetic kidney disease, hypertensive nephrosclerosis, GN, polycystic kidney disease, and other. Pairwise comparisons of the receiver operating characteristic curves by CKD etiology were performed to compare kidney failure risk equation discrimination.

RESULTS

The kidney failure risk equation provided adequate to excellent discrimination in identifying patients with CKD likely to progress to kidney failure at the 2- and 5-year time points both overall (2-year area under the curve, 0.83; 95% confidence interval, 0.81 to 0.85; 5-year area under the curve, 0.81; 95% confidence interval, 0.77 to 0.84) and across CKD etiologies. The kidney failure risk equation displayed adequate calibration at the 2- and 5-year time points both overall and across CKD etiologies (Hosmer-Lemeshow P≥0.05); however, the predicted risks of kidney failure were higher than the observed risks across CKD etiologies with the exception of polycystic kidney disease.

CONCLUSIONS

The kidney failure risk equation provides adequate discrimination and calibration in advanced CKD and across CKD etiologies.

Defining the susceptibility of colorectal cancers to BH3-mimetic compounds

Novel targets are required to improve the outcomes for patients with colorectal cancers. In this regard, the selective inhibitor of the pro-survival protein BCL2, venetoclax, has proven highly effective in several hematological malignancies. In addition to BCL2, potent and highly selective small molecule inhibitors of its relatives, BCLxL and MCL1, are now available, prompting us to investigate the susceptibility of colorectal cancers to the inhibition of one or more of these pro-survival proteins. While targeting BCLxL, but not BCL2 or MCL1, on its own had some impact, most (15/17) of the immortalized colorectal cancer cell lines studied were efficiently killed by the combined targeting of BCLxL and MCL1. Importantly, these in vitro findings were confirmed in a xenograft model and, interestingly, in all (5/5) patient derived tumor organoids evaluated. Our results lend strong support to the notion that BCLxL and MCL1 are highly promising targets for further evaluation in efforts to improve the treatment of colorectal cancers.

Simultaneous glomerular filtration rate determination using inulin, iohexol, and 99mTc-DTPA demonstrates the need for customized measurement protocols

Urinary inulin clearance is considered the gold standard of glomerular filtration rate (GFR) measurement but plasma clearance of less expensive and more accessible tracers is more commonly performed. Many plasma sampling protocols exist but little is known about their accuracy. Here, the study objectives were to compare plasma iohexol and ^99mTc-DTPA GFR with varying sampling strategies to the GFR measured by urinary inulin and to identify protocols with the greatest accuracy according to clinical characteristics. GFR was measured simultaneously using urinary inulin, plasma iohexol, and plasma ^99mTc DTPA clearance. Blood was sampled from 2 to 10 hours after injection. For each method, bias, precision, and accuracy (P30 and mean absolute error) were calculated for the entire cohort and for eGFR-EPI creatinine subgroups (<30, 30-59, and ≥60 ml/min/1.73m²) and the edema stage using urinary inulin clearance as the gold standard. The mean inulin GFR of the 77 participants was 33 ml/min/1.73m². Delay of both the initial and the final samples in plasma iohexol protocols yielded the highest accuracy in the setting of low GFR (<30 ml/min/1.73m²). Early initial and final samples yielded the highest accuracy in the setting of high GFRs (≥60 ml/min/1.73m²). No sampling strategy was accurate in edematous patients. Thus, our study demonstrates that customization of GFR protocols according to the anticipated level of GFR are required to optimize protocol accuracy.

Management of Advanced Chronic Kidney Disease During the COVID-19 Pandemic: Suggestions From the Canadian Society of Nephrology COVID-19 Rapid Response Team

PURPOSE OF PROGRAM

To provide guidance on the management of patients with advanced chronic kidney disease (CKD) not requiring kidney replacement therapy during the COVID-19 pandemic.

SOURCES OF INFORMATION

Program-specific documents, pre-existing, and related to COVID-19; documents from national and international kidney agencies; national and international webinars, including webinars that we hosted for input and feedback; with additional information from formal and informal review of published academic literature.

METHODS

Challenges in the care of patients with advanced CKD during the COVID-19 pandemic were highlighted within the Canadian Senior Renal Leaders Forum discussion group. The Canadian Society of Nephrology (CSN) developed the COVID-19 rapid response team (RRT) to address these challenges. They identified a lead with expertise in advanced CKD who identified further nephrologists and administrators to form the workgroup. A nation-wide survey of advanced CKD clinics was conducted. The initial guidance document was drafted and members of the workgroup reviewed and discussed all suggestions in detail via email and a virtual meeting. Disagreements were resolved by consensus. The document was reviewed by the CSN COVID-19 RRT, an ethicist and an infection control expert. The suggestions were presented at a CSN-sponsored interactive webinar, attended by 150 kidney health care professionals, for further peer input. The document was also sent for further feedback to experts who had participated in the initial survey. Final revisions were made based on feedback received until April 28, 2020. Canadian Journal of Kidney Health and Disease (CJKHD) editors reviewed the parallel process peer review and edited the manuscript for clarity.

KEY FINDINGS

We identified 11 broad areas of advanced CKD care management that may be affected by the COVID-19 pandemic: (1) clinic visit scheduling, (2) clinic visit type, (3) provision of multidisciplinary care, (4) bloodwork, (5) patient education/support, (6) home-based monitoring essentials, (7) new referrals to multidisciplinary care clinic, (8) kidney replacement therapy, (9) medications, (10) personal protective equipment, and (11) COVID-19 risk in CKD. We make specific suggestions for each of these areas.

LIMITATIONS

The suggestions in this paper are expert opinion, and subject to the biases associated with this level of evidence. To expedite the publication of this work, a parallel review process was created that may not be as robust as standard arms' length peer-review processes.

IMPLICATIONS

These suggestions are intended to provide guidance for advanced CKD directors, clinicians, and administrators on how to provide the best care possible during a time of altered priorities and reduced resources.

Relationship of coronary artery calcification with renal function decline and mortality in predialysis chronic kidney disease patients

BACKGROUND

Patients with chronic kidney disease (CKD) have higher levels of coronary artery calcification (CAC) compared with the general population. The role of CAC in renal function decline is not well understood.

METHODS

In this prospective cohort study of Stages 3-5 CKD patients with CAC scores kidney function decline, development of end-stage kidney disease (ESKD) and all-cause mortality were determined at 5 and 10 years. Baseline variables included markers of CKD and chronic kidney disease mineral and bone disorder (CKD-MBD), demographics and comorbidities. Multivariable analyses identified predictors of outcomes, and survival curves demonstrated the association of CAC score with ESKD and mortality.

RESULTS

One hundred and seventy-eight patients were enrolled between 2005 and 2007. Independent predictors of ESKD at 5 years were estimated glomerular filtration rate (eGFR) and urine albumin-creatinine ratio (UACR); at 10 years, eGFR was no longer a predictor, but CAC was now significant. Those who developed ESKD at the fastest rate either had the highest CAC score (≥400 AU) or were youngest and had the lowest calcidiol, and highest serum phosphate, UACR and percentage change in CAC per year. Predictors of eGFR decline over 5 years were UACR, parathyroid hormone and CAC score. Predictors of mortality at 5 years were age, diabetes and eGFR and at 10 years also included CAC score.

CONCLUSIONS

In Stages 3-5 CKD patients, CAC is an independent predictor of both ESKD and mortality at 10 years. Those who developed ESKD at the fastest rate either had the highest CAC score or the worst CKD-MBD derangements.

Accurate GFR in obesity-protocol for a systematic review

BACKGROUND

Obesity is increasing globally. Chronic kidney disease (CKD) is strongly associated with obesity. Kidney function is commonly estimated with equations using creatinine (such as CKD-EPI equation) which is a product of muscle metabolism. Decisions about categorizing CKD, planning modality of renal replacement therapies, and adjusting dosages of medications excreted by the kidneys are done using these equations. However, it is not well appreciated that creatinine-based equations may not accurately estimate kidney function in obese individuals. We plan a systematic review of diagnostic studies which will compare estimating equations to actual measured kidney function.

METHODS

We will systematically search electronic bibliographic databases including MEDLINE, EMBASE, and the Cochrane Library with no restrictions on language or specific dates. The search terms will be adapted for the different databases using a combination of Medical Subject Heading and relevant keywords contained in titles and abstracts. Our preliminary search strategy using Cochrane, MEDLINE, and EMBASE databases have identified 190, 1246, and 1660 citations, respectively. For all studies selected, we will extract information on general study characteristics, study participant (age, sex, ethnicity, weight, height, BMI, BSA), type and protocol of reference standard utilized, the index test studied, the methodology of measurement of index test, categories of GFR, the proportion of eGFR within 10, 20, 30, 40, and 50% of measured GFR, and bias between eGFR and measured GFR. If the quality of methods and risk of bias are adequate, we will perform a meta-analysis. We will assess the heterogeneity using the χ 2 and the I 2 statistics to examine whether the estimates from studies included could be pooled. Sensitivity and multivariate meta-regression analyses will be performed to assess the effects of clinical factors and socio-demographic characteristics reported in included studies on the meta-analytic estimates. All analysis will be performed using the Comprehensive Meta-analysis software.

DISCUSSION

This systematic review might help to inform clinicians on the best equation to use in patients with obesity and CKD for staging of CKD and for medication dosing. If no equation is deemed suitable, this review will form a basis for future studies of GFR in obese individuals.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42018104345.

Individual patient variability with the application of the kidney failure risk equation in advanced chronic kidney disease

The Kidney Failure Risk Equation (KFRE) predicts the need for dialysis or transplantation using age, sex, estimated glomerular filtration rate (eGFR), and urine albumin to creatinine ratio (ACR). The eGFR and ACR have known biological and analytical variability. We examined the effect of biological and analytical variability of eGFR and ACR on the 2-year KFRE predicted kidney failure probabilities using single measure and the average of repeat measures of simulated eGFR and ACR. Previously reported values for coefficient of variation (CV) for ACR and eGFR were used to calculate day to day variability. Variation was also examined with outpatient laboratory data from patients with an eGFR between 15 and 50 mL/min/1.72 m². A web application was developed to calculate and model day to day variation in risk. The biological and analytical variability related to ACR and eGFR lead to variation in the predicted probability of kidney failure. A male patient age 50, ACR 30 mg/mmol and eGFR 25, had a day to day variation in risk of 7% (KFRE point estimate: 17%, variability range 14% to 21%). The addition of inter laboratory variation due to different instrumentation increased the variability to 9% (KFRE point estimate 17%, variability range 13% to 22%). Averaging of repeated measures of eGFR and ACR significantly decreased the variability (KFRE point estimate 17%, variability range 15% to 19%). These findings were consistent when using outpatient laboratory data which showed that most patients had a KFRE 2-year risk variability of ≤ 5% (79% of patients). Approximately 13% of patients had variability from 5–10% and 8% had variability > 10%. The mean age (SD) of this cohort was 64 (15) years, 36% were females, the mean (SD) eGFR was 32 (10) ml/min/1.73m² and median (IQR) ACR was 22.7 (110). Biological and analytical variation intrinsic to the eGFR and ACR may lead to a substantial degree of variability that decreases with repeat measures. Use of a web application may help physicians and patients understand individual patient’s risk variability and communicate risk (https://mccudden.shinyapps.io/kfre_app/). The web application allows the user to alter age, gender, eGFR, ACR, CV (for both eGFR and ACR) as well as units of measurements for ACR (g/mol versus mg/g).

Serum BTP concentrations are not affected by hepatic dysfunction

Background

Beta Trace Protein (BTP) is a promising marker of glomerular filtration rate (GFR). Equations to estimate GFR using BTP have been proposed. Very little is known about BTP’s production and metabolism. It has been hypothesized that the liver metabolizes certain BTP isoforms. As such, hepatic dysfunction may influence serum levels independently of GFR. This would impact on the accuracy and precision of GFR estimates using BTP. The purpose of this study was to assess the impact of cirrhosis on serum BTP concentrations.

Methods

BTP, cystatin C (cysC) and creatinine (Cr) were measured in 99 cirrhotic subjects and in matched controls. BTP/cysC and Cr/cysC ratios were compared between cases and controls. This was repeated after stratification by Child Pugh category. Comparisons of ratios between Child Pugh category A and combined B and C case subjects were also performed.

Results

There were no differences in BTP/cysC ratios between cases and controls for the entire cohort (0.80 vs 0.79) or for any of the Child Pugh categories (p > 0.10). There were significant differences between cases (1.09) and controls (0.73) for the BTP/Cr ratios (p < 0.001). The BTP/Cr ratio was higher in those with more advanced cirrhosis as compared to those with less severe cirrhosis (1.20 vs 1.03, p < 0.01). There were no differences in BTP/cysC ratios between those with less severe and more advanced cirrhosis (p = 0.25).

Conclusions

This study suggests that hepatic dysfunction does not influence serum BTP levels and argues against a significant role for the liver in BTP metabolism. Confirmation in a larger group of patients with advanced cirrhosis is required.

Validation of a routine two-sample iohexol plasma clearance assessment of GFR and an evaluation of common endogenous markers in a rat model of CKD

Endogenous markers of kidney function are insensitive to early declines in glomerular filtration rate (GFR) and in rodent models, validated, practical alternatives are unavailable. In this study, we determined GFR by modeling the plasma clearance of two compounds, iohexol and inulin, and compared the findings to common endogenous markers. All plasma clearance methods of both iohexol and inulin detected a decline in renal function weeks prior to any increase in endogenous marker. Iohexol plasma clearance and inulin plasma clearance had a very high agreement and minimal bias when using 12‐sample models. However, only iohexol could be accurately simplified to a two‐sample, one‐compartment estimation strategy. Following an IV injection of low‐dose iohexol and two timed blood samples at 30 and 90 min, one can accurately approximate a complex 12‐sample strategy of plasma clearance. This method is simple enough to use in routine, longitudinal analysis of larger cohort animal studies.

Impaired Phosphate Tolerance Revealed With an Acute Oral Challenge

Elevated serum phosphate is consistently linked with cardiovascular disease (CVD) events and mortality in the setting of normal and impaired kidney function. However, serum phosphate does not often exceed the upper limit of normal until glomerular filtration rate (GFR) falls below 30 mL/min/m² . It was hypothesized that the response to an oral, bioavailable phosphate load will unmask impaired phosphate tolerance, a maladaptation not revealed by baseline serum phosphate concentrations. In this study, rats with varying kidney function as well as normo-phosphatemic human subjects, with inulin-measured GFR (13.2 to 128.3mL/min), received an oral phosphate load. Hormonal and urinary responses were evaluated over 2 hours. Results revealed that the more rapid elevation of serum phosphate was associated with subjects and rats with higher levels of kidney function, greater responsiveness to acute changes in parathyroid hormone (PTH), and significantly more urinary phosphate at 2 hours. In humans, increases in urinary phosphate to creatinine ratio did not correlate with baseline serum phosphate concentrations but did correlate strongly to early increase of serum phosphate. The blunted rise in serum phosphate in rats with CKD was not the result of altered absorption. This result suggests acute tissue deposition may be altered in the setting of kidney function impairment. Early recognition of impaired phosphate tolerance could translate to important interventions, such as dietary phosphate restriction or phosphate binders, being initiated at much higher levels of kidney function than is current practice. © 2017 American Society for Bone and Mineral Research.

Dispersal and assimilation of an aquaculture waste subsidy in a low productivity coastal environment

To understand dispersal and assimilation of aquaculture waste subsidies in a naturally low-productivity environment, we applied a novel, rapid transmethylation technique to analyse sediment and biota fatty acid composition. This technique was initially validated at Atlantic salmon farms in Macquarie Harbour, Australia, where sediments were collected at farm and control locations. Subsequently, sediment, benthic polychaete and zooplankton were sampled at sites 0, 50, 250, 500 and 1000m distant from multiple cages. Results demonstrated an acute deposition zone up to 50m from cages and a diffuse zone extending 500m from cages. Changes in sediment concentration of linoleic acid, oleic acid and total fatty acids were effective tracers of farm deposition. Bacterial biomarkers indicated that aquaculture waste stimulates bacterial productivity in sediments, with elevated biomarker concentrations also detected in benthic polychaetes. Overall, fatty acid analysis was a sensitive technique to characterize the benthic footprint of aquaculture influence.

Creatinine Assay Attainment of Analytical Performance Goals Following Implementation of IDMS Standardization: Further Improvements Required

BACKGROUND

The international initiative to standardize creatinine (Cr) assays by tracing reference materials to Isotope Dilution Mass Spectrometry (IDMS) assigned values was implemented to reduce interlaboratory variability and improve assay accuracy.

OBJECTIVE

The aims of this study were to examine whether IDMS standardization has improved Cr assay accuracy (bias), interlaboratory variability (precision), total error (TE), and attainment of recommended analytical performance goals.

METHODS

External Quality Assessment (EQA) data (n = 66 challenge vials) from Ontario, Canada, were analyzed. The bias, precision, TE, and the number of EQA challenge vials meeting performance goals were determined by assay manufacturer before (n = 32) and after (n = 34) IDMS implementation.

RESULTS

The challenge vials with the worst bias and precision were spiked with known common interfering substances (glucose and bilirubin). IDMS standardization improved assay bias (10.4%-1.6%, P < .001), but precision remained unchanged (5.0%-4.7%, P = .5) with performance goals not consistently being met. Precision and TE goals based on biologic variation were attained by only 29% to 69% and 32% to 62% of challenge vials.

CONCLUSIONS

While IDMS standardization has improved Cr assay accuracy and thus reduced TE, significant interlaboratory variability remains. Contemporary Cr assays do not currently meet the standards required to allow for accurate and consistent estimated glomerular filtration rate assessment and chronic kidney disease diagnosis across laboratories. Further improvements in Cr assay performance are needed.

Interlaboratory Variability in Plasma Creatinine Measurement and the Relation with Estimated Glomerular Filtration Rate and Chronic Kidney Disease Diagnosis

BACKGROUND AND OBJECTIVES

The tracing of creatinine (Cr) reference materials to isotope dilution mass spectrometry-assigned values was implemented worldwide to reduce interlaboratory variability and improve assay accuracy. The aims of this study were to examine the current extent of interlaboratory variability and its effect on eGFR.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Leftover plasma from 2-3 consecutive days was obtained from 53 intensive care unit patients with a range of kidney functions. Individual patient samples were pooled and split and sent to 12 different laboratories for Cr measurement. For each patient, the mean Cr and Chronic Kidney Disease Epidemiology Collaboration eGFR (eGFR-EPI), assuming a 65-year-old nonblack woman, were determined. Interlaboratory variability was assessed by the range and SD of Cr and eGFR-EPI. This was repeated after stratifying by assay type and by the median Cr of 1.36 mg/dl. For patients whose eGFR-EPI range included 60 ml/min per 1.73 m2, the percentage of laboratories with eGFR-EPI<60 ml/min per 1.73 m2 was determined.

RESULTS

The mean±SD of the Cr and eGFR-EPI ranges were 0.20±0.09 mg/dl and 14±9 ml/min per 1.73 m2 for Cr<1.36 mg/dl. Jaffe Cr results were an average 0.1 mg/dl (Cr≥1.36 mg/dl) and 0.05 mg/dl (Cr<1.36 mg/dl) higher than enzymatic results (P<0.001 for both). Ten patients had an eGFR-EPI range that included 60 ml/min per 1.73 m2. Their median eGFR-EPI range was 15 ml/min per 1.73 m2. There was significant discordance in the diagnosis of CKD (eGFR-EPI<60 ml/min per 1.73 m2), with laboratories using Jaffe Cr methods making the diagnosis more frequently than those using enzymatic Cr methods (60% versus 39%).

CONCLUSIONS

Significant interlaboratory variability in Cr measurement still exists. Jaffe assays yield higher Cr values than enzymatic assays, leading to lower eGFR-EPIs and more frequent CKD diagnoses. Further improvements in assay performance are required to standardize patient CKD diagnosis and to facilitate longitudinal Cr monitoring across laboratories.

Classification of Kidney Transplant Recipients Using a Combination of Estimated GFR and Albuminuria Reflects Risk

BACKGROUND

The 2012 Kidney Dialysis Initiative Global Outcomes chronic kidney disease (CKD) classification scheme subdivides stage 3 CKD and incorporates the urinary albumin-to-creatinine ratio (ACR). The aim of this study was to evaluate whether the novel scheme provides graded risk in kidney transplant recipients (KTRs).

METHODS

Prevalent KTRs with available laboratory data were included. The primary outcome was a composite of doubling of serum creatinine, graft failure, or death. Patients were stratified using the CKD-Epidemiolgic Collaboration equation, and ACR and the event rate per 1000 patient-years in each CKD category were calculated.

RESULTS

There were 269 KTRs with a mean follow-up of 4.5 ± 2.0 years. There was a graded increase in outcomes with increasing ACR and decreasing estimated glomerular filtration rate (eGFR). For the primary outcome, the event rate was 15.3 (95% confidence interval, 4.2-39.2) per 1000 patient-years for those with an eGFR greater than 60 mL/min per 1.73 m2 and an ACR less than 30 mg/g, whereas it was 375 (95% confidence interval, 193.8-655.1) for those with an eGFR less than 30 mL/min per 1.73 m2 and an ACR greater than 300 mg/g.

CONCLUSIONS

The novel Kidney Dialysis Initiative Global Outcomes classification scheme provides graded risk for important clinical events in KTRs. This information can be used to identify high-risk patients and to tailor follow-up and management strategies aimed at improving outcomes.

Phosphate excretion is decreased in older cardiac patients with normal kidney function: an emerging dietary risk factor?

Serum phosphate independently predicts cardiovascular events and mortality. Sixteen healthy adults and 9 adults with cardiovascular disease (CVD) ingested 500 mg of sodium phosphate after an over-night fast. In control subjects, the urine phosphate/creatinine ratio was significantly higher at 2 h (3.12 ± 1.02) than at baseline (1.98 ± 0.58, p < 0.001) but no change was observed in CVD patients. Decreased postprandial urinary excretion of phosphate could accelerate vascular calcification and may be an under-recognized risk factor for CVD.

Oral salt and water versus intravenous saline for the prevention of acute kidney injury following contrast-enhanced computed tomography: study protocol for a pilot randomized trial

Background

Although intravenous saline is the accepted prophylactic measure for the prevention of contrast- induced acute kidney injury, the oral route could offer an equivalent, practical, and cost saving approach. A systematic review of randomized trials that compared oral versus intravenous volume expansion for the prevention of radiocontrast-induced nephropathy in patients receiving arterial contrast reported no significant difference in the risk of contrast induced acute kidney injury between the oral and intravenous arms. Most trials for contrast nephropathy prevention have been in the setting of arterial contrast such as with cardiac catheterization, and not with venous contrast, such as computed tomography. The aim of this paper is to describe the protocol of a pilot trial comparing the effect of oral salt and water versus intravenous saline on the prevention of Acute Kidney Injury following contrast-enhanced computed tomography.

Methods

Our study is a pilot, single-centre parallel randomized controlled trial. To be included, participants must be at stage 4 of chronic kidney disease as defined by a glomerular filtration rate <30 mL/min/1.73 m², aged greater than 18 years and to undergo an outpatient contrast-enhanced computer tomography of the chest or abdomen. A total 50 patients will be randomised to receive either oral salt and water or intravenous isotonic saline. The primary outcome is feasibility, including estimates of recruitment rate, adherence to intervention and completeness of follow-up to assist in planning the definitive trial. The secondary outcome is safety and includes adverse events with oral salt and water loading as compared to intravenous isotonic saline.

Discussion

The results of this pilot trial will provide critical information to plan a definitive trial to test the efficacy of the route of volume loading regimens in prevention of acute kidney injury after contrast-enhanced CT scans.

Trial registration

The trial is registered at the US National Institutes of Health (ClinicalTrials.gov) # NCT02084771.

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.

Varenicline induced acute interstitial nephritis in the setting of idiopathic membranous glomerulonephritis

Background

Varenicline is a nicotinic receptor partial agonist indicated for the cessation of smoking. It is regarded as having no or minimal renal toxicity. A single case report has linked it to acute interstitial nephritis.

Case presentation

A 56 year-old female with a long-standing history of idiopathic membranous glomerulonephritis presented on routine follow-up with an unexpected rise in her serum creatinine from a stable baseline of 225 umol/L to 319 umol/L Biopsy revealed acute interstitial nephritis. There were no preceding clinical events other than the initiation of varenicline therapy three months prior. This was discontinued with no improvement in renal function. A ten week course of prednisone was initiated and creatinine levels returned to baseline. Shortly after prednisone therapy was completed, renal function worsened but the patient declined further immunosuppressive therapy. Exposure to varenicline therapy two years prior had also resulted in a reversible decline in kidney function.

Conclusion

This is only the second case report to document varenicline-induced acute interstitial nephritis. A careful medication history and renal biopsy were essential in identifying the etiology of the acute kidney injury in this patient with a complex renal history.

SOCS3: An essential physiological inhibitor of signaling by interleukin-6 and G-CSF family cytokines

SOCS3 is an inducible negative feedback inhibitor of cytokine signaling. Conditional deletion of SOCS3 in mice using the Cre-lox system has now been applied to a range of cell types in the steady-state and under inflammatory, pathogenic, or tumorigenic stress, with the resulting phenotypes demonstrating the effects of SOCS3 in physiological and disease contexts. Together with recent structural and biochemical studies on the mechanisms of SOCS3 binding to cytokine receptors and associated kinases, we now have a better understanding of the non-redundant roles of SOCS3 in the inhibition of cytokine signaling via the receptors gp130, G-CSFR, leptinR, and IL-12Rβ. This review discusses the known functional activities of SOCS3 in fertility and development, inflammation, innate and adaptive immunity, and malignancy as determined by genetic studies in mice.

Kidney function endpoints in kidney transplant trials: a struggle for power

Kidney function endpoints are commonly used in randomized controlled trials (RCTs) in kidney transplantation (KTx). We conducted this study to estimate the proportion of ongoing RCTs with kidney function endpoints in KTx where the proposed sample size is large enough to detect meaningful differences in glomerular filtration rate (GFR) with adequate statistical power. RCTs were retrieved using the key word "kidney transplantation" from the National Institute of Health online clinical trial registry. Included trials had at least one measure of kidney function tracked for at least 1 month after transplant. We determined the proportion of two-arm parallel trials that had sufficient sample sizes to detect a minimum 5, 7.5 and 10 mL/min difference in GFR between arms. Fifty RCTs met inclusion criteria. Only 7% of the trials were above a sample size of 562, the number needed to detect a minimum 5 mL/min difference between the groups should one exist (assumptions: α = 0.05; power = 80%, 10% loss to follow-up, common standard deviation of 20 mL/min). The result increased modestly to 36% of trials when a minimum 10 mL/min difference was considered. Only a minority of ongoing trials have adequate statistical power to detect between-group differences in kidney function using conventional sample size estimating parameters. For this reason, some potentially effective interventions which ultimately could benefit patients may be abandoned from future assessment.

Accuracy of cystatin C-based estimates of glomerular filtration rate in kidney transplant recipients: a systematic review

BACKGROUND

As with creatinine, cystatin C can be incorporated into a formula to estimate the glomerular filtration rate (GFR). The overall performance of cystatin C-based equations in kidney transplantation is unclear with conflicting results between studies.

METHODS

Systematic review of adult kidney transplant recipients. Studies that reported mean bias (mean difference between the measured and estimated GFRs) or accuracy of the cystatin C-based GFR estimation equation (e.g. percentage of estimates within 30% of the measured GFR) against the measured GFR using renal or plasma clearance of contrast agents, radioisotopes or inulin were included.

RESULTS

The search identified 10 studies that examined 14 different cystatin C-based estimating equations (n = 5 equations evaluated in more than one study). The Le Bricon equation had the best performance with a bias that ranged from -6.4 to +2.8 mL/min/1.73 m(2); 85% (95% CI, 82-88) of estimates were within 30% of the measured GFR. For the other equations, 66-82% of estimates were within 30% of the measured GFR. For the modification of diet in renal disease (MDRD) equation, 68% (95% CI, 65-72) of estimates were within 30% of the measured GFR.

CONCLUSIONS

The cystatin C-based Le Bricon equation was the most accurate, and most of the cystatin C-based equations showed improvements in 30% and 50% accuracy compared with the creatinine-based MDRD equation. Cystatin C-based equations may offer an advantage over the MDRD equation in kidney transplant recipients. Estimating equations re-expressed with standardized cystatin C have been developed and their accuracy needs to be tested in the kidney transplant population.