The safety of a low protein diet in older adults with advanced chronic kidney disease.

BACKGROUND: A low protein diet (LPD) is recommended to patients with advanced chronic kidney disease (CKD), whereas geriatric guidelines recommend a higher amount of protein. The aim of this study was to evaluate the safety of LPD treatment in older adults with advanced CKD. METHODS: The EQUAL study is a prospective, observational study, including patients ≥65 years, incident estimated glomerular filtration rate <20 ml/min/1.73m², in six European countries with follow-up up till six years. Nutritional status was assessed by 7-point subjective global assessment (SGA) every 3-6 months. Prescribed diet (gram protein/kilogram/bodyweight) was recorded on every study visit; measured protein intake was available in three countries. Time to death and decline in nutritional status (SGA decrease by ≥2 points) were analysed using marginal structural models with dynamic inverse probability of treatment and censoring weights. RESULTS: Out of 1738 adults (631 prescribed LPD at any point during follow-up) there were 1319 with repeated SGA measurements of which 267 (20%) declined in SGA ≥ 2 points and 565 (32.5%) died. There was no difference in survival or decline in nutritional status for patients prescribed LPD ≤0.8 g/kg ideal bodyweight (Odds Ratio (OR) for mortality 1.15 (95% Confidence interval (CI) 0.86-1.55) and OR for decline in SGA 1.11 (95% CI 0.74-1.66) in the adjusted models. In patients prescribed LPD <0.6 g/kg ideal bodyweight, the results were similar. There was a significant interaction with LPD and higher age >75 years, lower SGA, and higher comorbidity burden for both mortality and nutritional status decline. CONCLUSIONS: In older adults with CKD approaching end-stage kidney disease, a traditional LPD prescribed and monitored according to routine clinical practice in Europe appears to be safe.

Changes in the epidemiology of kidney replacement therapy across Europe in 2020 - the first year of the COVID-19 pandemic: an ERA Registry study.

BACKGROUND: In 2020, the COVID-19 pandemic caused disruptions in kidney replacement therapy (KRT) services worldwide. The aim of this study was to assess the effect of the COVID-19 pandemic in 2020 on the incidence of KRT, kidney transplantation activity, mortality and prevalence of KRT across Europe. METHODS: Patients receiving KRT were included from 17 countries providing data to the European Renal Association Registry. The epidemiology of KRT in 2020 was compared with average data from the period 2017-2019. Also changes occurring during the first and second wave of the pandemic were explored. RESULTS: The incidence of KRT was 6.2% lower in 2020 compared with 2017-2019, with the lowest point (-22.7%) during the first wave in April. The decrease varied across countries, was smaller in males (-5.2%) than in females (-8.2%), and was moderate for peritoneal dialysis (-3.7%) and haemodialysis (-5.4%), but substantial for pre-emptive kidney transplantation (-23.6%). The kidney transplantation rate decreased by 22.5%, reaching a nadir of -80.1% during the first wave, and most for living donor kidney transplants (-30.5%). While in most countries the kidney transplantation rate decreased, in the Nordic/Baltic countries and Greece there was no clear decline. In dialysis patients, mortality increased by 11.4%, and was highest in those aged 65-74 years (16.1%), in those with diabetes as primary renal disease (15.1%), and in those on haemodialysis (12.4%). In transplant recipients, the mortality was 25.8% higher, but there were no subgroups that stood out. In contrast to the rising prevalence of KRT observed over the past decades across Europe, the prevalence at the end of 2020 (N=317787) resembled that of 2019 (N=317077). CONCLUSION: The COVID-19 pandemic has had a substantial impact on the incidence of KRT, kidney transplant activity, mortality of KRT, and prevalence of KRT in Europe with variations across countries.

Serum Potassium and Risk of Death or Kidney Replacement Therapy in Older People With CKD Stages 4-5: Eight-Year Follow-up.

RATIONALE & OBJECTIVE: Hypokalemia may accelerate kidney function decline. Both hypo- and hyperkalemia can cause sudden cardiac death. However, little is known about the relationship between serum potassium and death or the occurrence of kidney failure requiring replacement therapy (KRT). We investigated this relationship in older people with chronic kidney disease (CKD) stage 4-5. STUDY DESIGN: Prospective observational cohort study. SETTING & PARTICIPANTS: We followed 1,714 patients (≥65 years old) from the European Quality (EQUAL) study for 8 years from their first estimated glomerular filtration rate (eGFR)<20mL/min/1.73m2 measurement. EXPOSURE: Serum potassium was measured every 3 to 6 months and categorized as≤3.5,>3.5-≤4.0,>4.0-≤4.5,>4.5-≤5.0 (reference),>5.0-≤5.5, >5.5-≤6.0, and>6.0mmol/L. OUTCOME: The combined outcome death before KRT or start of KRT. ANALYTICAL APPROACH: The association between categorical and continuous time-varying potassium and death or KRT start was examined using Cox proportional hazards and restricted cubic spline analyses, adjusted for age, sex, diabetes, cardiovascular disease, renin-angiotensin-aldosterone system (RAAS) inhibition, eGFR, and subjective global assessment (SGA). RESULTS: At baseline, 66% of participants were men, 42% had diabetes, 47% cardiovascular disease, and 54% used RAAS inhibitors. Their mean age was 76±7 (SD) years, mean eGFR was 17±5 (SD) mL/min/1.73m2, and mean SGA was 6.0±1.0 (SD). Over 8 years, 414 (24%) died before starting KRT, and 595 (35%) started KRT. Adjusted hazard ratios for death or KRT according to the potassium categories were 1.6 (95% CI, 1.1-2.3), 1.4 (95% CI, 1.1-1.7), 1.1 (95% CI, 1.0-1.4), 1 (reference), 1.1 (95% CI, 0.9-1.4), 1.8 (95% CI, 1.4-2.3), and 2.2 (95% CI, 1.5-3.3). Hazard ratios were lowest at a potassium of about 4.9mmol/L. LIMITATIONS: Shorter intervals between potassium measurements would have allowed for more precise estimations. CONCLUSIONS: We observed a U-shaped relationship between serum potassium and death or KRT start among patients with incident CKD 4-5, with a nadir risk at a potassium level of 4.9mmol/L. These findings underscore the potential importance of preventing both high and low potassium in patients with CKD 4-5. PLAIN-LANGUAGE SUMMARY: Abnormal potassium blood levels may increase the risk of death or kidney function decline, especially in older people with chronic kidney disease (CKD). We studied 1,714 patients aged≥65 years with advanced CKD from the European Quality (EQUAL) study and followed them for 8 years. We found that both low and high levels of potassium were associated with an increased risk of death or start of kidney replacement therapy, with the lowest risk observed at a potassium level of 4.9 mmol/L. In patients with CKD, the focus is often on preventing high blood potassium. However, this relatively high optimum potassium level stresses the potential importance of also preventing low potassium levels in older patients with advanced CKD.

Clinical and patient-reported trajectories at end-of-life in older patients with advanced CKD.

BACKGROUND: We explore longitudinal trajectories of clinical indicators, patient-reported outcomes, and hospitalizations, in the years preceding death in a population of older patients with advanced chronic kidney disease (CKD). METHODS: The EQUAL study is a European observational prospective cohort study with an incident eGFR <20 ml/min per 1.73 m2 and ≥65 years of age. The evolution of each clinical indicator was explored using generalized additive models during the 4 years preceding death. RESULTS: We included 661 decedents with a median time to death of 2.0 years (IQR 0.9-3.2). During the years preceding death, eGFR, Subjective Global Assessment score, and blood pressure declined, with accelerations seen at 6 months preceding death. Serum hemoglobin, hematocrit, cholesterol, calcium, albumin, and sodium values declined slowly during follow-up, with accelerations observed between 6 and 12 months preceding death. Physical and mental quality of life declined linearly throughout follow-up. The number of reported symptoms was stable up to 2 years prior to death, with an acceleration observed at 1 year prior to death. The rate of hospitalization was stable at around one hospitalization per person year, increasing exponentially at 6 months preceding death. CONCLUSIONS: We identified clinically relevant physiological accelerations in patient trajectories that began ∼6 to 12 months prior to death, which are likely multifactorial in nature, but correlate with a surge in hospitalizations. Further research should focus on how to effectively use this knowledge to inform patient and family expectations, to benefit the planning of (end-of-life) care, and to establish clinical alert systems.

Association between CKD-MBD and mortality in older patients with advanced CKD-results from the EQUAL study.

BACKGROUND: Chronic kidney disease-mineral and bone disorder (CKD-MBD) is a common complication of CKD; it is associated with higher mortality in dialysis patients, while its impact in non-dialysis patients remains mostly unknown. We investigated the associations between parathyroid hormone (PTH), phosphate and calcium (and their interactions), and all-cause, cardiovascular (CV) and non-CV mortality in older non-dialysis patients with advanced CKD. METHODS: We used data from the European Quality study, which includes patients aged ≥65 years with estimated glomerular filtration rate ≤20 mL/min/1.73 m2 from six European countries. Sequentially adjusted Cox models were used to assess the association between baseline and time-dependent CKD-MBD biomarkers and all-cause, CV and non-CV mortality. Effect modification between biomarkers was also assessed. RESULTS: In 1294 patients, the prevalence of CKD-MBD at baseline was 94%. Both PTH [adjusted hazard ratio (aHR) 1.12, 95% confidence interval (CI) 1.03-1.23, P = .01] and phosphate (aHR 1.35, 95% CI 1.00-1.84, P = .05), but not calcium (aHR 1.11, 95% CI 0.57-2.17, P = .76), were associated with all-cause mortality. Calcium was not independently associated with mortality, but modified the effect of phosphate, with the highest mortality risk found in patients with both hypercalcemia and hyperphosphatemia. PTH level was associated with CV mortality, but not with non-CV mortality, whereas phosphate was associated with both CV and non-CV mortality in most models. CONCLUSIONS: CKD-MBD is very common in older non-dialysis patients with advanced CKD. PTH and phosphate are independently associated with all-cause mortality in this population. While PTH level is only associated with CV mortality, phosphate seems to be associated with both CV and non-CV mortality.

Work status and work ability of patients receiving kidney replacement therapy: results from a European survey.

BACKGROUND: Employment is important for the quality of life and financial security of patients of working age receiving kidney replacement therapy (KRT). We aimed to examine self-reported work status and general, physical and mental work ability and to determine associations between demographic, disease-related, work-related and macroeconomic factors and employment. . METHODS: Europeans from 37 countries, ages 19-65 years, treated with dialysis or kidney transplantation, filled out the web-based or paper-based cross-sectional EDITH kidney patient survey between November 2017 and January 2019. We performed descriptive analyses and multivariable generalized logistic mixed models. RESULTS: Of the 3544 patients, 36.5% were employed and working [25.8% of dialysis patients, 53.9% of kidney transplant recipients (KTRs)]. The mean general work ability was 5.5 out of 10 (dialysis: 4.8, KTRs: 6.5). Non-working patients (all: 4.1, dialysis: 3.9, KTRs: 4.7) scored lower than working patients (all: 7.7, dialysis 7.3, KTRs: 8.0). Working dialysis patients scored lower on physical and mental work ability (7.1 and 8.1) than working KTRs (8.0 and 8.4; P < 0.001). Impaired physical work ability (42.7%) was more prevalent than impaired mental work ability (26.7%). Male sex, age 40-49 years, higher education, home dialysis or kidney transplantation as current treatment, treatment history including kidney transplantation, absence of diabetes mellitus, better general work ability and higher country gross domestic product were positively associated with employment (P < 0.05). CONCLUSIONS: Low employment rates and impaired work ability were prevalent among European patients receiving KRT. Demographic, disease-related, work-related and macro-economic factors were associated with employment.

Using datasets to ascertain the generalizability of clinical cohorts: the example of the European QUALity study on the treatment of advanced chronic kidney disease.

BACKGROUND: Cohort studies are among the most robust of observational studies but have issues with external validity. This study assesses threats to external validity (generalizability) in the European QUALity (EQUAL) study, a cohort study of people >65 years of age with Stage 4/5 chronic kidney disease. METHODS: Patients meeting the EQUAL inclusion criteria were identified in The Health Improvement Network database and stratified into those attending renal units, a secondary care cohort (SCC) and a not primary care cohort (PCC). Survival, progression to renal replacement therapy (RRT) and hospitalization were compared. RESULTS: The analysis included 250, 633 and 2464 patients in EQUAL, PCC and SCC. EQUAL had a higher proportion of men compared with PCC and SCC (60.0% versus 34.8% versus 51.4%). Increasing age ≥85 years {odds ratio [OR] 0.25 [95% confidence interval (CI) 0.15-0.40]} and comorbidity [Charlson Comorbidity Index ≥4, OR 0.69 (95% CI 0.52-0.91)] were associated with non-participation in EQUAL. EQUAL had a higher proportion of patients starting RRT at 1 year compared with SCC (8.1% versus 2.1%; P < 0.001). Patients in the PCC and SCC had increased risk of hospitalization [incidence rate ratio 1.76 (95% CI 1.27-2.47) and 2.13 (95% CI 1.59-2.86)] and mortality at 1 year [hazard ratio 3.48 (95% CI 2.1-5.7) and 1.7 (95% CI 1.1-2.7)] compared with EQUAL. CONCLUSIONS: This study provides evidence of how participants in a cohort study can differ from the broader population of patients, which is essential when considering external validity and application to local practice.

Converting from face-to-face to postal follow-up and its effects on participant retention, response rates and errors: lessons from the EQUAL study in the UK.

BACKGROUND: Prospective cohort studies are challenging to deliver, with one of the main difficulties lying in retention of participants. The need to socially distance during the COVID-19 pandemic has added to this challenge. The pre-COVID-19 adaptation of the European Quality (EQUAL) study in the UK to a remote form of follow-up for efficiency provides lessons for those who are considering changing their study design. METHODS: The EQUAL study is an international prospective cohort study of patients ≥65 years of age with advanced chronic kidney disease. Initially, patients were invited to complete a questionnaire (SF-36, Dialysis Symptom Index and Renal Treatment Satisfaction Questionnaire) at research clinics every 3-6 months, known as "traditional follow-up" (TFU). In 2018, all living patients were invited to switch to "efficient follow-up" (EFU), which used an abbreviated questionnaire consisting of SF-12 and Dialysis Symptom Index. These were administered centrally by post. Response rates were calculated using returned questionnaires as a proportion of surviving invitees, and error rates presented as the average percentage of unanswered questions or unclear answers, of total questions in returned questionnaires. Response and error rates were calculated 6-monthly in TFU to allow comparisons with EFU. RESULTS: Of the 504 patients initially recruited, 236 were still alive at the time of conversion to EFU; 111 of these (47%) consented to the change in follow-up. In those who consented, median TFU was 34 months, ranging from 0 to 42 months. Their response rates fell steadily from 88% (98/111) at month 0 of TFU, to 20% (3/15) at month 42. The response rate for the first EFU questionnaire was 60% (59/99) of those alive from TFU. With this improvement in response rates, the first EFU also lowered errors to baseline levels seen in early follow-up, after having almost trebled throughout traditional follow-up. CONCLUSIONS: Overall, this study demonstrates that administration of shorter follow-up questionnaires by post rather than in person does not negatively impact patient response or error rates. These results may be reassuring for researchers who are trying to limit face-to-face contact with patients during the COVID-19 pandemic.

Patient-Reported Measures and Lifestyle Are Associated With Deterioration in Nutritional Status in CKD Stage 4-5: The EQUAL Cohort Study.

OBJECTIVE: The aim of this study was to explore the changes in nutritional status before dialysis initiation and to identify modifiable risk factors of nutritional status decline in older adults with advanced renal disease. DESIGN AND METHODS: The European Quality Study on treatment in advanced chronic kidney disease (EQUAL) is a prospective, observational cohort study involving six European countries. We included 1,103 adults >65 years with incident estimated glomerular filtration rate <20 mL/min/1.73 m2 not on dialysis, attending nephrology care. Nutritional status was assessed with the 7-point Subjective Global Assessment tool (7-p SGA), patient-reported outcomes with RAND-36 and the Dialysis Symptom Index. Logistic regression was used to estimate the associations between potential risk factors and SGA decline. RESULTS: The majority of the patients had a normal nutritional status at baseline, 28% were moderately malnourished (SGA ≤5). Overall, mean SGA decreased by -0.18 points/year, (95% confidence interval -0.21; -0.14). More than one-third of the study participants (34.9%) deteriorated in nutritional status (1 point decline in SGA) and 10.9% had a severe decline in SGA (≥2 points). The proportion of patients with low SGA (≤5) increased every 6 months. Those who dropped in SGA also declined in estimated glomerular filtration rate and mental health score. Every 10 points decrease in physical function score increased the odds of decline in SGA by 23%. Lower physical function score at baseline, gastrointestinal symptoms, and smoking were risk factors for impaired nutritional status. There was an interaction between diabetes and physical function on SGA decline. CONCLUSIONS: Nutritional status deteriorated in more than one-third of the study participants during the first year of follow-up. Lower patient-reported physical function, more gastrointestinal symptoms, and current smoking were associated with decline in nutritional status.

Kidney Failure Prediction Models: A Comprehensive External Validation Study in Patients with Advanced CKD.

BACKGROUND: Various prediction models have been developed to predict the risk of kidney failure in patients with CKD. However, guideline-recommended models have yet to be compared head to head, their validation in patients with advanced CKD is lacking, and most do not account for competing risks. METHODS: To externally validate 11 existing models of kidney failure, taking the competing risk of death into account, we included patients with advanced CKD from two large cohorts: the European Quality Study (EQUAL), an ongoing European prospective, multicenter cohort study of older patients with advanced CKD, and the Swedish Renal Registry (SRR), an ongoing registry of nephrology-referred patients with CKD in Sweden. The outcome of the models was kidney failure (defined as RRT-treated ESKD). We assessed model performance with discrimination and calibration. RESULTS: The study included 1580 patients from EQUAL and 13,489 patients from SRR. The average c statistic over the 11 validated models was 0.74 in EQUAL and 0.80 in SRR, compared with 0.89 in previous validations. Most models with longer prediction horizons overestimated the risk of kidney failure considerably. The 5-year Kidney Failure Risk Equation (KFRE) overpredicted risk by 10%-18%. The four- and eight-variable 2-year KFRE and the 4-year Grams model showed excellent calibration and good discrimination in both cohorts. CONCLUSIONS: Some existing models can accurately predict kidney failure in patients with advanced CKD. KFRE performed well for a shorter time frame (2 years), despite not accounting for competing events. Models predicting over a longer time frame (5 years) overestimated risk because of the competing risk of death. The Grams model, which accounts for the latter, is suitable for longer-term predictions (4 years).

Development and testing of an artificial intelligence tool for predicting end-stage kidney disease in patients with immunoglobulin A nephropathy.

We have developed an artificial neural network prediction model for end-stage kidney disease (ESKD) in patients with primary immunoglobulin A nephropathy (IgAN) using a retrospective cohort of 948 patients with IgAN. Our tool is based on a two-step procedure of a classifier model that predicts ESKD, and a regression model that predicts development of ESKD over time. The classifier model showed a performance value of 0.82 (area under the receiver operating characteristic curve) in patients with a follow-up of five years, which improved to 0.89 at the ten-year follow-up. Both models had a higher recall rate, which indicated the practicality of the tool. The regression model showed a mean absolute error of 1.78 years and a root mean square error of 2.15 years. Testing in an independent cohort of 167patients with IgAN found successful results for 91% of the patients. Comparison of our system with other mathematical models showed the highest discriminant Harrell C index at five- and ten-years follow-up (81% and 86%, respectively), paralleling the lowest Akaike information criterion values (355.01 and 269.56, respectively). Moreover, our system was the best calibrated model indicating that the predicted and observed outcome probabilities did not significantly differ. Finally, the dynamic discrimination indexes of our artificial neural network, expressed as the weighted average of time-dependent areas under the curve calculated at one and two years, were 0.80 and 0.79, respectively. Similar results were observed over a 25-year follow-up period. Thus, our tool identified individuals who were at a high risk of developing ESKD due to IgAN and predicted the time-to-event endpoint. Accurate prediction is an important step toward introduction of a therapeutic strategy for improving clinical outcomes.

Mortality in Children Treated With Maintenance Peritoneal Dialysis: Findings From the International Pediatric Peritoneal Dialysis Network Registry.

RATIONALE & OBJECTIVE: Research on pediatric kidney replacement therapy (KRT) has primarily focused on Europe and North America. In this study, we describe the mortality risk of children treated with maintenance peritoneal dialysis (MPD) in different parts of the world and characterize the associated demographic and macroeconomic factors. STUDY DESIGN: Prospective cohort study. SETTING & PARTICIPANTS: Patients younger than 19 years at inclusion into the International Pediatric Peritoneal Dialysis Network registry, who initiated MPD between 1996 and 2017. EXPOSURE: Region as primary exposure (Asia, Western Europe, Eastern Europe, Latin America, North America, and Oceania). Other demographic, clinical, and macroeconomic (4 income groups based on gross national income) factors also were studied. OUTCOME: All-cause MPD mortality. ANALYTICAL APPROACH: Patients were observed for 3 years, and the mortality rates in different regions and income groups were calculated. Cause-specific hazards models with random effects were fit to calculate the proportional change in variance for factors that could explain variation in mortality rates. RESULTS: A total of 2,956 patients with a median age of 7.8 years at the start of KRT were included. After 3 years, the overall probability of death was 5%, ranging from 2% in North America to 9% in Eastern Europe. Mortality rates were higher in low-income countries than in high-income countries. Income category explained 50.1% of the variance in mortality risk between regions. Other explanatory factors included peritoneal dialysis modality at start (22.5%) and body mass index (11.1%). LIMITATIONS: The interpretation of interregional survival differences as found in this study may be hampered by selection bias. CONCLUSIONS: This study shows that the overall 3-year patient survival on pediatric MPD is high, and that country income is associated with patient survival.

Kidney function and symptom development over time in elderly patients with advanced chronic kidney disease: results of the EQUAL cohort study.

BACKGROUND: Initiation of renal replacement therapy often results from a combination of kidney function deterioration and symptoms related to chronic kidney disease (CKD) progression. We investigated the association between kidney function decline and symptom development in patients with advanced CKD. METHODS: In the European Quality study on treatment in advanced CKD (EQUAL study), a European prospective cohort study, patients with advanced CKD aged ≥65 years and a kidney function that dropped <20 mL/min/1.73 m2 were followed for 1 year. Linear mixed-effects models were used to assess the association between kidney function decline and symptom development. The sum score for symptom number ranged from 0 to 33 and for overall symptom severity from 0 to 165, using the Dialysis Symptom Index. RESULTS: At least one kidney function estimate with symptom number or overall symptom severity was available for 1109 and 1019 patients, respectively. The mean (95% confidence interval) annual kidney function decline was 1.70 (1.32; 2.08) mL/min/1.73 m2. The mean overall increase in symptom number and severity was 0.73 (0.28; 1.19) and 2.93 (1.34; 4.52) per year, respectively. A cross-sectional association between the level of kidney function and symptoms was lacking. Furthermore, kidney function at cohort entry was not associated with symptom development. However, each mL/min/1.73 m2 of annual kidney function decline was associated with an extra annual increase of 0.23 (0.07; 0.39) in the number of symptoms and 0.87 (0.35; 1.40) in overall symptom severity. CONCLUSIONS: A faster kidney function decline was associated with a steeper increase in both symptom number and severity. Considering the modest association, our results seem to suggest that repeated thorough assessment of symptom development during outpatient clinic visits, in addition to the monitoring of kidney function decline, is important for clinical decision-making.

Renal function decline in older men and women with advanced chronic kidney disease-results from the EQUAL study.

INTRODUCTION: Understanding the mechanisms underlying the differences in renal decline between men and women may improve sex-specific clinical monitoring and management. To this end, we aimed to compare the slope of renal function decline in older men and women in chronic kidney disease (CKD) Stages 4 and 5, taking into account informative censoring related to the sex-specific risks of mortality and dialysis initiation. METHODS: The European QUALity Study on treatment in advanced CKD (EQUAL) study is an observational prospective cohort study in Stages 4 and 5 CKD patients ≥65 years not on dialysis. Data on clinical and demographic patient characteristics were collected between April 2012 and December 2018. Estimated glomerular filtration rate (eGFR) was calculated using the CKD Epidemiology Collaboration equation. eGFR trajectory by sex was modelled using linear mixed models, and joint models were applied to deal with informative censoring. RESULTS: We included 7801 eGFR measurements in 1682 patients over a total of 2911 years of follow-up. Renal function declined by 14.0% [95% confidence interval (CI) 12.9-15.1%] on average each year. Renal function declined faster in men (16.2%/year, 95% CI 15.9-17.1%) compared with women (9.6%/year, 95% CI 6.3-12.1%), which remained largely unchanged after accounting for various mediators and for informative censoring due to mortality and dialysis initiation. Diabetes was identified as an important determinant of renal decline specifically in women. CONCLUSION: In conclusion, renal function declines faster in men compared with women, which remained similar after adjustment for mediators and despite a higher risk of informative censoring in men. We demonstrate a disproportional negative impact of diabetes specifically in women.

International prescribing patterns and polypharmacy in older people with advanced chronic kidney disease: results from the European Quality study.

BACKGROUND: People with chronic kidney disease (CKD) are at high risk of polypharmacy. However, no previous study has investigated international prescribing patterns in this group. This article aims to examine prescribing and polypharmacy patterns among older people with advanced CKD across the countries involved in the European Quality (EQUAL) study. METHODS: The EQUAL study is an international prospective cohort study of patients ≥65 years of age with advanced CKD. Baseline demographic, clinical and medication data were analysed and reported descriptively. Polypharmacy was defined as ≥5 medications and hyperpolypharmacy as ≥10. Univariable and multivariable linear regressions were used to determine associations between country and the number of prescribed medications. Univariable and multivariable logistic regression were used to determine associations between country and hyperpolypharmacy. RESULTS: Of the 1317 participants from five European countries, 91% were experiencing polypharmacy and 43% were experiencing hyperpolypharmacy. Cardiovascular medications were the most prescribed medications (mean 3.5 per person). There were international differences in prescribing, with significantly greater hyperpolypharmacy in Germany {odds ratio (OR) 2.75 [95% confidence interval (CI) 1.73-4.37]; P < 0.001, reference group UK}, the Netherlands [OR 1.91 (95% CI 1.32-2.76); P = 0.001] and Italy [OR 1.57 (95% CI 1.15-2.15); P = 0.004]. People in Poland experienced the least hyperpolypharmacy [OR 0.39 (95% CI 0.17-0.87); P = 0.021]. CONCLUSIONS: Hyperpolypharmacy is common among older people with advanced CKD, with significant international differences in the number of medications prescribed. Practice variation may represent a lack of consensus regarding appropriate prescribing for this high-risk group for whom pharmacological treatment has great potential for harm as well as benefit.

Points of attention when conducting etiological research.

Epidemiological studies often aim to investigate the causal contribution of a risk factor to a disease or other outcome. In etiological research, one is usually interested in the (biological) mechanism(s) underlying the studied relationship. Inappropriate conduct of an etiological study may have major implications for the correctness of the results and interpretation of the findings. Therefore, in this paper, we aim to describe step by step how etiological research should be carried out, together with its  common pitfalls. These steps involve finding and formulating a well-defined etiological research question, choosing an appropriate study design including a suitable comparison group, adequate modelling, and adequate reporting and interpretation of the results.

Results from the ERA-EDTA Registry indicate a high mortality due to COVID-19 in dialysis patients and kidney transplant recipients across Europe.

The aim of this study was to investigate 28-day mortality after COVID-19 diagnosis in the European kidney replacement therapy population. In addition, we determined the role of patient characteristics, treatment factors, and country on mortality risk with the use of ERA-EDTA Registry data on patients receiving kidney replacement therapy in Europe from February 1, 2020, to April 30, 2020. Additional data on all patients with a diagnosis of COVID-19 were collected from 7 European countries encompassing 4298 patients. COVID-19-attributable mortality was calculated using propensity score-matched historic control data and after 28 days of follow-up was 20.0% (95% confidence interval 18.7%-21.4%) in 3285 patients receiving dialysis and 19.9% (17.5%-22.5%) in 1013 recipients of a transplant. We identified differences in COVID-19 mortality across countries, and an increased mortality risk in older patients receiving kidney replacement therapy and male patients receiving dialysis. In recipients of kidney transplants ≥75 years of age, 44.3% (35.7%-53.9%) did not survive COVID-19. Mortality risk was 1.28 (1.02-1.60) times higher in transplant recipients compared with matched dialysis patients. Thus, the pandemic has had a substantial effect on mortality in patients receiving kidney replacement therapy, a highly vulnerable population due to underlying chronic kidney disease and a high prevalence of multimorbidity.

Results in the ESPN/ERA-EDTA Registry suggest disparities in access to kidney transplantation but little variation in graft survival of children across Europe.

One of the main objectives of the European health policy framework is to ensure equitable access to high-quality health services across Europe. Here we examined country-specific kidney transplantation and graft failure rates in children and explore their country- and patient-level determinants. Patients under 20 years of age initiating kidney replacement therapy from January 2007 through December 2015 in 37 European countries participating in the ESPN/ERA-EDTA Registry were included in the analyses. Countries were categorized as low-, middle-, and high-income based on gross domestic product. At five years of follow-up, 4326 of 6909 children on kidney replacement therapy received their first kidney transplant. Overall median time from kidney replacement therapy start to first kidney transplantation was 1.4 (inter quartile range 0.3-4.3) years. The five-year kidney transplantation probability was 48.8% (95% confidence interval: 45.9-51.7%) in low-income, 76.3% (72.8-79.5%) in middle-income and 92.3% (91.0-93.4%) in high-income countries and was strongly associated with macro-economic factors. Gross domestic product alone explained 67% of the international variation in transplantation rates. Compared with high-income countries, kidney transplantation was 76% less likely to be performed in low-income and 58% less likely in middle-income countries. Overall five-year graft survival in Europe was 88% and showed little variation across countries. Thus, despite large disparities transplantation access across Europe, graft failure rates were relatively similar. Hence, graft survival in low-risk transplant recipients from lower-income countries seems as good as graft survival among all (low-, medium-, and high-risk) graft recipients from high-income countries.

Where to look for the most frequent biases?

Study quality depends on a number of factors, one of them being internal validity. Such validity can be affected by random and systematic error, the latter also known as bias. Both make it more difficult to assess a correct frequency or the true relationship between exposure and outcome. Where random error can be addressed by increasing the sample size, a systematic error in the design, the conduct or the reporting of a study is more problematic. In this article, we will focus on bias, discuss different types of selection bias (sampling bias, confounding by indication, incidence-prevalence bias, attrition bias, collider stratification bias and publication bias) and information bias (recall bias, interviewer bias, observer bias and lead-time bias), indicate the type of studies where they most frequently occur and provide suggestions for their prevention.

Intention to treat and per protocol analysis in clinical trials.

In clinical epidemiology, experimental studies usually take the form of randomized controlled clinical trials (RCTs). The data analysis of an RCT can be performed by using two complementary strategies, that is according to the intention to treat (ITT) principle and the per protocol (PP) analysis. By using the ITT approach, investigators aim to assess the effect of assigning a drug whereas by adopting the PP analysis, researchers investigate the effect of receiving the assigned treatment, as specified in the protocol. Both ITT and PP analyses are essentially valid but they have different scopes and interpretations dependent on the context.