AQP1 Promoter Variant, Water Transport, and Outcomes in Peritoneal Dialysis

BACKGROUND

Variability in ultrafiltration influences prescriptions and outcomes in patients with kidney failure who are treated with peritoneal dialysis. Variants in AQP1, the gene that encodes the archetypal water channel aquaporin-1, may contribute to that variability.

METHODS

We gathered clinical and genetic data from 1851 patients treated with peritoneal dialysis in seven cohorts to determine whether AQP1 variants were associated with peritoneal ultrafiltration and with a risk of the composite of death or technique failure (i.e., transfer to hemodialysis). We performed studies in cells, mouse models, and samples obtained from humans to characterize an AQP1 variant and investigate mitigation strategies.

RESULTS

The common AQP1 promoter variant rs2075574 was associated with peritoneal ultrafiltration. Carriers of the TT genotype at rs2075574 (10 to 16% of patients) had a lower mean (±SD) net ultrafiltration level than carriers of the CC genotype (35 to 47% of patients), both in the discovery phase (506±237 ml vs. 626±283 ml, P = 0.007) and in the validation phase (368±603 ml vs. 563±641 ml, P = 0.003). After a mean follow-up of 944 days, 139 of 898 patients (15%) had died and 280 (31%) had been transferred to hemodialysis. TT carriers had a higher risk of the composite of death or technique failure than CC carriers (adjusted hazard ratio, 1.70; 95% confidence interval [CI], 1.24 to 2.33; P = 0.001), as well as a higher risk of death from any cause (24% vs. 15%, P = 0.03). In mechanistic studies, the rs2075574 risk variant was associated with decreases in AQP1 promoter activity, aquaporin-1 expression, and glucose-driven osmotic water transport. The use of a colloid osmotic agent mitigated the effects of the risk variant.

CONCLUSIONS

A common variant in AQP1 was associated with decreased ultrafiltration and an increased risk of death or technique failure among patients treated with peritoneal dialysis. (Funded by the Swiss National Science Foundation and others.).

Modeling Length of Stay as an Optimized Two-class Prediction Problem

Objectives: To develop a predictive model for the outcome length of stay at the Intensive Care Unit (ICU LOS), including the choice of an optimal dichotomization threshold for this outcome. Reduction of prediction problems of this type of outcome to a two-class problem is a common strategy to identify high-risk patients.

Methods: Threshold selection and model development are performed simultaneously. From the range of possible threshold values, the value is chosen for which the corresponding predictive model has maximal precision based on the data. To compare the precision of models for different dichotomizations of the outcome, the MALOR performance statistic is introduced. This statistic is insensitive to the prevalence of positive cases in a two-class prediction problem.

Results: The procedure is applied to data from cardiac surgery patients to dichotomize the outcome ICU LOS. The class probabilitytree method is used to develop predictive models. Within our data, the best model precision is found at the threshold of seven days.

Conclusions: The presented method extends existing procedures for predictive modeling with optimization of the outcome definition for predictive purposes. The method can be applied to all prediction problems where the outcome variable needs to be dichotomized, and is insensitive to changes in the prevalence of positive cases with different dichotomization thresholds.

Single nucleotide variants in the protein C pathway and mortality in dialysis patients

BACKGROUND

The protein C pathway plays an important role in the maintenance of endothelial barrier function and in the inflammatory and coagulant processes that are characteristic of patients on dialysis. We investigated whether common single nucleotide variants (SNV) in genes encoding protein C pathway components were associated with all-cause 5 years mortality risk in dialysis patients.

METHODS

Single nucleotides variants in the factor V gene (F5 rs6025; factor V Leiden), the thrombomodulin gene (THBD rs1042580), the protein C gene (PROC rs1799808 and 1799809) and the endothelial protein C receptor gene (PROCR rs867186, rs2069951, and rs2069952) were genotyped in 1070 dialysis patients from the NEtherlands COoperative Study on the Adequacy of Dialysis (NECOSAD) cohort) and in 1243 dialysis patients from the German 4D cohort.

RESULTS

Factor V Leiden was associated with a 1.5-fold (95% CI 1.1-1.9) increased 5-year all-cause mortality risk and carriers of the AG/GG genotypes of the PROC rs1799809 had a 1.2-fold (95% CI 1.0-1.4) increased 5-year all-cause mortality risk. The other SNVs in THBD, PROC, and PROCR were not associated with 5-years mortality.

CONCLUSION

Our study suggests that factor V Leiden and PROC rs1799809 contributes to an increased mortality risk in dialysis patients.

Role of hemostatic factors on the risk of venous thrombosis in people with impaired kidney function

BACKGROUND

Factors explaining the association between impaired kidney function and venous thrombosis have not been identified so far. The aim of our study was to determine whether the association between impaired kidney function and venous thrombosis can be explained by the concurrent presence of genetic or acquired venous thrombosis risk factors.

METHODS AND RESULTS

The glomerular filtration rate was estimated (eGFR) in 2473 venous thrombosis patients and 2936 controls from a population-based case-control study. Kidney function was grouped into 6 categories based on percentiles of the eGFR in the controls (>50th [reference], 10th-50th, 5th-10th, 2.5th-5th, 1st-2.5th, and <1st percentile). Several hemostatic factors showed a procoagulant shift with decreasing kidney function in controls, most notably factor VIII and von Willebrand factor. Compared with eGFR >50th percentile, factor VIII levels (adjusted mean difference, 60 IU/dL for the <1st eGFR percentile category) and von Willebrand factor levels (adjusted mean difference, 60 IU/dL for the <1st eGFR percentile category) increased with each percentile category. The odds ratios for venous thrombosis similarly increased across the categories from 1.1 (95% confidence interval, 0.9-1.3) for the 10th to 50th percentile to 3.7 (95% confidence interval, 2.4-5.7) for the <1st percentile category. Adjustment for factor VIII or von Willebrand factor attenuated these odds ratios, indicating an effect of eGFR on thrombosis through these factors. Adjustments for other risk factors for venous thrombosis did not affect the odds ratios.

CONCLUSION

Impaired kidney function affects venous thrombosis risk via concurrently raised factor VIII and von Willebrand factor levels.

PERMANENT GENETIC RESOURCES: Polymorphic microsatellite loci and interspecific cross-amplification in the parasitoid wasps Megastigmus stigmatizans and Megastigmus dorsalis

We isolated and characterized 19 polymorphic microsatellite loci in the congeneric parasitoid wasps Megastigmus stigmatizans and Megastigmus dorsalis associated with cynipid oak galls. Loci isolated from species-specific libraries showed extensive cross-amplification, resulting in a total of 15 polymorphic loci for M. stigmatizans and 13 for M. dorsalis.

Type of arteriovenous vascular access and association with patency and mortality

BACKGROUND

There are only a few risk factors known for primary patency loss in patients with an arteriovenous graft or fistula. Furthermore, a limited number of studies have investigated the association between arteriovenous access modality and primary patency loss and mortality. The aim of this study was to investigate risk factors for patency loss and to investigate the association between graft versus fistula use and outcomes (patency loss and mortality).

METHODS

We prospectively followed 919 incident hemodialysis patients and calculated hazard ratios (HRs) for putative risk factors of primary patency loss using Cox regression. Furthermore, HRs were calculated to study the association between graft versus fistula use and two-year primary patency loss and two-year mortality.

RESULTS

Cardiovascular disease, prior catheter use, lowest tertile of albumin, highest tertile of hsCRP, and lowest tertile of fetuin-A were associated with primary patency loss in both patients with grafts and fistulas. Increased age, female sex, and diabetes mellitus were only associated with primary patency loss in patients with a fistula. We did not observe an association between primary patency loss and BMI, residual GFR, levels of calcium, phosphorus, and total cholesterol. Furthermore, graft use as compared with fistula use was associated with an 1.4-fold (95% CI 1.0-1.9) increased risk of primary patency loss and with an 1.5-fold(95% CI 1.0-2.2) increased mortality risk.

CONCLUSION

Cardiovascular disease, prior catheter use, albumin, hsCRP, and fetuin-A are risk factors for patency loss. Graft use as compared with fistula use was associated with an increased risk of patency loss and mortality.

Risk of venous thrombosis in patients with chronic kidney disease: identification of high-risk groups

BACKGROUND

Although an association between venous thrombosis and chronic kidney disease has recently been established, it is unknown which patients with chronic kidney disease are most likely to benefit from thromboprophylaxis.

OBJECTIVE

The aim of this study was to assess the association between venous thrombosis and chronic kidney disease in combination with arterial thrombosis, malignancy, surgery and thrombophilia to identify high-risk groups as a basis for personalized prevention.

METHODS

This study included 2473 consecutive patients with first venous thrombosis and 2936 controls from a case-control study (the MEGA study).

RESULTS

Moderately decreased kidney function (eGFR 30-60 mL min(-1) ) was associated with a 2.5-fold (95% CI, 1.9-3.4) increased risk and severely decreased kidney function (eGFR < 30 mL min(-1) ) was associated with a 5.5-fold (95% CI 1.8-16.7) increased risk of venous thrombosis, compared with those with normal kidney function (eGFR > 90 mL min(-1) ). The risk of venous thrombosis was additionally increased for moderately and severely reduced kidney function in combination with arterial thrombosis (odds ratio, 4.9; 95% CI, 2.2-10.9), malignancy (5.8; 95% CI, 2.8-12.1), surgery (14.0; 95%, CI 5.0-39.4), immobilization (17.1; 95% CI, 6.8-43.0) or thrombophilia (odds ratios, 4.3-9.5), with particularly high risks when three or more risk factors were present (odds ratio, 56.3; 95% CI, 7.6-419.3).

CONCLUSION

Decreased kidney function is associated with an increased risk of venous thrombosis. The risk increased substantially in the presence of one or more other risk factors for thrombosis.

Risk of venous thrombosis in patients with major illnesses: results from the MEGA study

BACKGROUND

The risk of venous thrombosis associated with major illnesses is not well known, and neither is the risk associated with the combined effect of immobilization and thrombophilia. The aim of this study was to assess the effect on the development of venous thrombosis of several major illnesses in combination with immobilization, body mass index, and thrombophilia, to identify high-risk groups that may provide a basis for personalized prevention.

METHODS

This study included 4311 consecutive patients with a first episode of venous thrombosis, and 5768 controls from a case-control study (MEGA study). We calculated odds ratios (ORs) for venous thrombosis for patients with a self-reported history of major illnesses.

RESULTS

Venous thrombosis risk was increased for all investigated major illnesses: liver disease, OR 1.7 (95% confidence interval [CI]1.0-2.9); kidney disease, OR 3.7 (95% CI 2.3-5.9); rheumatoid arthritis, OR 1.5 (95% CI 1.2-1.9); multiple sclerosis, OR 2.4 (95% CI 1.3-4.3); heart failure, OR 1.7 (95% CI 1.2-2.3); hemorrhagic stroke, OR 4.9 (95% CI 2.4-9.9); arterial thrombosis, OR 1.5 (95% CI 1.2-1.8); and the presence of any of the above major illnesses, OR 1.7 (95% CI 1.5-1.9). Combinations of major illnesses with immobilization and increased factor VIII (OR 79.9; 95% CI 33.2-192.2), increased FIX (OR 35.3; 95% CI 14.2-87.8), increased von Willebrand factor (OR 88.0; 95% CI 33.9-228.3), FV Leiden (OR 84.2; 95% CI 19.5-363.6), and blood group non-O (OR 53.1; 95% CI 30.9-91.4) were associated with increased venous thrombosis risks.

CONCLUSIONS

All of the major illnesses reported here were associated with an increased risk of venous thrombosis. These risks were most pronounced at the time of immobilization or in the presence of thrombophilia.

Mortality due to pulmonary embolism, myocardial infarction, and stroke among incident dialysis patients

BACKGROUND

It is has been suggested that dialysis patients have lower mortality rates for pulmonary embolism than the general population, because of platelet dysfunction and bleeding tendency. However, there is limited information whether dialysis is indeed associated with a decreased mortality risk from pulmonary embolism.

OBJECTIVE

The aim of our study was to evaluate whether mortality rate ratios for pulmonary embolism were lower than for myocardial infarction and stroke in dialysis patients compared with the general population.

METHODS

Cardiovascular causes of death for 130,439 incident dialysis patients registered in the ERA-EDTA Registry were compared with the cardiovascular causes of death for the European general population.

RESULTS

The age- and sex-standardized mortality rate (SMR) from pulmonary embolism was 12.2 (95% CI 10.2-14.6) times higher in dialysis patients than in the general population. The SMRs in dialysis patients compared with the general population were 11.0 (95% CI 10.6-11.4) for myocardial infarction, 8.4 (95% CI 8.0-8.8) for stroke, and 8.3 (95% CI 8.0-8.5) for other cardiovascular diseases. In dialysis patients, primary kidney disease due to diabetes was associated with an increased mortality risk due to pulmonary embolism (HR 1.9; 95% CI 1.0-3.8), myocardial infarction (HR 4.1; 95% CI 3.4-4.9), stroke (HR 3.5; 95% CI 2.8-4.4), and other cardiovascular causes of death (HR 3.4; 95% CI 2.9-3.9) compared with patients with polycystic kidney disease.

CONCLUSIONS

Dialysis patients were found to have an unexpected highly increased mortality rate for pulmonary embolism and increased mortality rates for myocardial infarction and stroke.

Estimation and asymptotic theory for transition probabilities in Markov renewal multi-state models

In this paper we discuss estimation of transition probabilities for semi-Markov multi-state models. Non-parametric and semi-parametric estimators of the transition probabilities for a large class of models (forward going models) are proposed. Large sample theory is derived using the functional delta method and the use of resampling is proposed to derive confidence bands for the transition probabilities. The last part of the paper concerns the presentation of the main ideas of the R implementation of the proposed estimators, and data from a renal replacement study are used to illustrate the behavior of the estimators proposed.

The -174G/C variant of IL6 as risk factor for mortality and technique failure in a large cohort of peritoneal dialysis patients

BACKGROUND

Functional variants in the IL6 gene, in particular the -174G/C polymorphism (rs1800795), affect the mortality risk in dialysis patients. Peritoneal dialysis (PD) patients harbouring the C allele of the -174G/C polymorphism of IL6 showed faster peritoneal transport. The aim of this study was to investigate this IL6 variant as risk factor for mortality and technique failure in a large cohort of Caucasian PD patients.

METHODS

A Dutch multicentre cohort of 398 incident PD patients (NECOSAD) was analysed. Survival analysis was performed for death and technique failure with a maximum follow-up of 5 years. A combined PD cohort from Amsterdam (Academic Medical Center, N = 71) and Brussels (Université catholique de Louvain Medical School, N = 102) was used for independent replication.

RESULTS

In NECOSAD, 105 patients died on dialysis [incidence rate 10.3/100 person-years (py)], and 138 patients experienced technique failure (16.2/100 py), with peritonitis as important cause. Patients with the C/C genotype had a 71% increased mortality risk compared to patients with the G/G genotype (95% confidence interval 0.98-2.98); this effect was mainly a long-term effect: a 2.7-fold increased mortality risk was found in patients having survived 2 years since the start on dialysis, and a 1.7-fold increased risk for the combined end point (mortality or technique failure). In the combined replication cohort, no increased risks were found in patients with the C/C genotype.

CONCLUSIONS

The C/C genotype of the -174G/C polymorphism was associated with an increased mortality risk in 398 Dutch incident PD patients. The existence of substantial differences between the two academic replication cohorts and the discovery cohort from NECOSAD and the limited power of these cohorts prevented an independent replication of the NECOSAD findings.

Time course of peritoneal function in automated and continuous peritoneal dialysis

BACKGROUND AND OBJECTIVES

In automated peritoneal dialysis (APD), a patient's peritoneal membrane is more intensively exposed to fresh dialysate than it is in continuous ambulatory peritoneal dialysis (CAPD). Our aim was to study, in incident peritoneal dialysis (PD) patients, the influence of APD-compared with that of CAPD-on peritoneal transport over 4 years.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

Patients were included if at least 2 annual standard permeability analyses (SPAs) performed with 3.86% glucose were available while the patient was using the same modality with which they had started PD (APD or CAPD). Patients were followed until their first modality switch. Differences in the pattern of SPA outcomes over time were tested using repeated-measures models adjusted for age, sex, comorbidity, primary kidney disease, and year of PD start.

RESULTS

The 59 CAPD patients enrolled were older than the 47 APD patients enrolled (mean age: 58 ± 14 years vs 49 ± 14 years; p < 0.01), and they had started PD earlier (mean start year: 2000 vs 2002). Over time, no differences in solute (p > 0.19) or fluid transport (p > 0.13) were observed. Similarly, free water transport (p = 0.43) and small-pore transport (p = 0.31) were not different between the modalities. Over time, patients on APD showed a faster decline in effective lymphatic absorption rate (ELAR: p = 0.02) and in transcapillary ultrafiltration (TCUF: p = 0.07, adjusted p = 0.05). Further adjustment did not change the results.

CONCLUSIONS

Compared with patients starting on CAPD, those starting on APD experienced a faster decline in ELAR and TCUF. Other transport parameters were not different over time between the groups.

The role of psychosocial factors in ethnic differences in survival on dialysis in the Netherlands

INTRODUCTION

Ethnic minority patients on dialysis are reported to have better survival rates relative to Caucasians. The reasons for this finding are not fully understood and European studies are scarce. This study examined whether ethnic differences in survival could be explained by patient characteristics, including psychosocial factors.

METHODS

We analysed data of the Netherlands Cooperative Study on the Adequacy of Dialysis study, an observational prospective cohort study of patients who started dialysis between 1997 and 2007 in the Netherlands. Ethnicity was classified as Caucasian, Black or Asian, assessed by local nurses. Data collected at the start of dialysis treatment included demographic, clinical and psychosocial characteristics. Psychosocial characteristics included data on health-related quality of life (HRQoL), mental health status and general health perception. Cox proportional hazards analysis was used to explore ethnic survival differences.

RESULTS

One thousand seven hundred and ninety-one patients were Caucasian, 45 Black and 108 Asian. The ethnic groups differed significantly in age, residual glomerular filtration rate, diabetes mellitus, erythropoietin use, plasma calcium, parathormone and creatinine, marital status and general health perception. No ethnic differences were found in HRQoL and mental health status. Crude hazard ratios (HRs) for mortality for Caucasians compared to Blacks and Asians were 3.1 [95% confidence interval (CI) 1.6-5.9] and 1.1 (95% CI 0.9-1.5), respectively. After adjustment for a range of potential explanatory variables, including psychosocial factors, the HRs were 2.5 (95% CI 1.2-4.9) compared with Blacks and 1.2 (95% CI 0.9-1.6) compared with Asians.

CONCLUSIONS

Although patient numbers were rather small, this study demonstrates, with 95% confidence, better survival for Black compared to Caucasian dialysis patients and equal survival for Asian compared to Caucasian dialysis patients in the Netherlands. This could not be explained by patient characteristics, including psychosocial factors.

Cardiovascular and noncardiovascular mortality among men and women starting dialysis

BACKGROUND AND OBJECTIVES

Although women have a survival advantage in the general population, women on dialysis have similar mortality to men. We hypothesized that this paired mortality risk during dialysis may be explained by a relative excess of cardiovascular-related mortality in women.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We compared 5-year age-stratified cardiovascular and noncardiovascular mortality rates, relative risks, and hazard ratios in a European cohort of incident adult dialysis patients (European Renal Association-European Dialysis and Transplant Association [ERA-EDTA] Registry) with the European general population (Eurostat). Cause of death was recorded by ERA-EDTA codes in dialysis patients and by International Statistical Classification of Diseases codes in the general population.

RESULTS

Overall, sex did not have a predictive effect on outcome in dialysis. Stratification into age categories and causes of death showed greater noncardiovascular mortality in young women (<45 years). In other age categories (45 to 55 and >55 years), women presented lower cardiovascular mortality. This cardiovascular benefit was, however, smaller than in the general population. Stratification by diabetic nephropathy showed that diabetic women in all age categories remained at increased mortality risk compared with men, an effect mainly attributed to the noncardiovascular component.

CONCLUSIONS

Mortality rates and causes of death in men and women on dialysis vary with age. Increased noncardiovascular mortality may explain the loss of the survival advantage of women on dialysis. Both young and diabetic women starting dialysis are at a higher mortality risk than equal men.

Venous and arterial thrombosis in dialysis patients

Whether the risk of both venous and arterial thrombosis is increased in dialysis patients as compared to the general population is unknown. In addition, it is unknown which subgroups are at highest risk. Furthermore, it is unknown whether having a history of venous thrombosis or arterial thrombosis prior to dialysis treatment increases mortality risk. A total of 455 dialysis patients were followed for objectively verified symptomatic thrombotic events between January 1997 and June 2009. The incidence rates in dialysis patients as compared to the general population was 5.6-fold (95% CI 3.1-8.9) increased for venous thrombosis, 11.9-fold (95% CI 9.3-14.9) increased for myocardial infarction, and 8.4-fold (95% CI 5.7-11.5) increased for ischaemic stroke. The combination of haemodialysis, lowest tertile of albumin, history of venous thrombosis, and malignancy was associated with subsequent venous thrombosis. Increased age, renal vascular disease, diabetes, high cholesterol levels, history of venous thrombosis, and history of arterial thrombosis were associated with subsequent arterial thrombosis. The all-cause mortality risk was 1.9-fold (95% CI 1.1-3.3) increased for patients with a history of venous thrombosis and 1.9-fold (95% CI 1.4-2.6) increased for patients with a history of arterial thrombosis. A potential limitation of this study was that in some risk categories associations with venous thrombosis did not reach statistical significance due to small numbers. In conclusion, dialysis patients have clearly elevated risks of venous thrombosis and arterial thrombosis and occurrence of venous thrombosis or arterial thrombosis prior to the start of dialysis is associated with an increased mortality risk.

Genetic association studies: discovery of the genetic basis of renal disease

Genetic association studies are a means to investigate the causal role of genes in diseases in order to unravel pathways involved in the etiology of disease. There are two types of genetic association studies: hypothesis-driven studies, i.e. candidate gene studies, targeting genes with a known or presumed role in pathways or diseases of interest, and non-hypothesis-driven studies, i.e. genome-wide association studies, aiming for the discovery of new genetic associations. This educational article is an introduction to genetic association studies for nephrologists and researchers in the domain of kidney disease.

Bone alkaline phosphatase and mortality in dialysis patients

BACKGROUND AND OBJECTIVES

Serum alkaline phosphatase (AP) is associated with vascular calcification and mortality in hemodialysis patients, but AP derives from various tissues of origin. The aim of this study was to assess the effect of bone-specific AP (BAP) on morbidity and mortality in dialysis patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

From a prospective cohort study of incident dialysis patients in The Netherlands, all patients with measured BAP at 12 months after the start of dialysis (baseline) were included in the analysis (n = 800; mean age, 59 ± 15 years; mean BAP = 18 ± 13 U/L). By Cox regression analyses, we assessed the impact of BAP levels on short-term mortality (6 months) and longer-term mortality (4-year follow-up).

RESULTS

High levels of BAP strongly affected short-term mortality. After adjustment for confounders, patients in the highest BAP tertile had a 5.7-fold increased risk of death within 6 months compared with patients in the lowest tertile. The effect applied to both cardiovascular and noncardiovascular mortality. Furthermore, high levels of BAP were associated with increased cardiovascular mortality in the longer term. In comparison with total AP, the effect sizes related to clinical outcomes were much higher for BAP.

CONCLUSIONS

High levels of BAP were strongly associated with short-term mortality in dialysis patients, pointing out the important impact of bone turnover. Longitudinal assessments of BAP may be useful for the treatment monitoring in clinical practice in dialysis patients.

Decline in residual renal function in automated compared with continuous ambulatory peritoneal dialysis

BACKGROUND AND OBJECTIVES

We compared the decline of RRF in patients starting dialysis on APD with those starting on CAPD, because a faster decline on APD has been suggested.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

NECOSAD patients starting dialysis on APD or CAPD with RRF at baseline were included and followed for 3 years. Residual GFR (rGFR) was the mean of urea and creatinine clearances. Differences in yearly decline of rGFR were estimated in analyses with linear repeated measures models, whereas the risk of complete loss of RRF was estimated by calculating hazard ratios (HRs) for APD compared with CAPD. As-treated (AT) and intention-to-treat (ITT) designs were used. All of the analyses were adjusted for age, gender, comorbidity, and primary kidney disease and stratified according to follow-up and mean baseline GFR.

RESULTS

The 505 CAPD and 78 APD patients had no major baseline differences. No differences were found in the analyses on yearly decline of rGFR. APD patients did have a higher risk of losing RRF in the first year (ITT crude HR 2.43 [confidence interval 95%, 1.48 to 4.00], adjusted 2.66 [1.60 to 4.44]; AT crude 1.89 [1.04 to 3.45], adjusted 2.15 [1.16 to 3.98]). The higher risk of losing all RRF was most pronounced in patients with the highest rGFR at baseline (ITT; crude 3.91 [1.54 to 9.94], adjusted 1.85 to 14.17).

CONCLUSIONS

The risk of losing RRF is higher for patients starting dialysis on APD compared with those starting on CAPD, especially in the first year.

Quality of life in automated and continuous ambulatory peritoneal dialysis

OBJECTIVE

Despite a lack of strong evidence, automated peritoneal dialysis (APD) is often prescribed on account of an expected better quality of life (QoL) than that expected with continuous ambulatory peritoneal dialysis (CAPD). Our aim was to analyze differences in QoL in patients starting dialysis on APD or on CAPD with a follow-up of 3 years.

METHODS

Adult patients in the prospective NECOSAD cohort who started dialysis on APD or CAPD were included 3 months after the start of dialysis. The Medical Outcomes Survey Short Form 36 [SF-36 (Medical Outcomes Trust and QualityMetric, Lincoln, RI, USA)] and Kidney Disease and Quality of Life Short Form [KDQOL-SF (KDQOL Working Group, Santa Monica, CA, USA)] questionnaires were used to measure QoL. Differences in QoL over time were calculated using linear mixed models. Patients were followed until transplantation, death, or a first switch to any other dialysis modality.

RESULTS

The clinical and social characteristics of the 64 APD and 486 CAPD patients were slightly different at baseline. In the crude analysis, the pattern of the mental summary score differed between the modalities (p = 0.03, adjusted p = 0.06), because of a different pattern for role function emotional (p = 0.03, adjusted p = 0.05). The pattern of the physical summary score was not different between the groups. Scores on dialysis staff encouragement had a different pattern over time (p = 0.01), because of an inequality in scores 3 months after the start of dialysis, which disappeared after 18 months on dialysis. Over time, patients on APD scored higher on sexual function. After adjustment for age, sex, glomerular filtration rate, comorbidity, and primary kidney disease, that difference disappeared. This study showed no major differences in QoL on the KDQOL-SF and the SF-36 between the two modalities.

Haemodialysis catheters increase mortality as compared to arteriovenous accesses especially in elderly patients

BACKGROUND

Catheter use has been associated with an increased mortality risk in haemodialysis patients. However, differences in the all-cause and cause-specific mortality risk between catheter use and arteriovenous access use in young and elderly haemodialysis patients have not yet been investigated.

METHODS

In this prospective cohort study of 1109 incident haemodialysis patients from 38 centres in the Netherlands, hazard ratios (HRs) with 95% confidence intervals (95% CIs) were calculated for 2-year all-cause, infection-related and cardiovascular mortality in patients with a catheter as compared to patients with an arteriovenous access stratified for age (< 65 years and ≥ 65 years).

RESULTS

Of the 1109 patients, 919 had an arteriovenous access and 190 had a catheter. The mortality rate was 76 per 1000 person-years in young patients with an arteriovenous access, 129 per 1000 person-years in young patients with a catheter, 222 per 1000 person-years in elderly patients with an arteriovenous access and 427 per 1000 person-years in elderly patients with a catheter. The adjusted HR was 3.15 (95% CI: 2.09-4.75) for elderly patients with a catheter as compared to young patients with an arteriovenous access. The adjusted HRs in elderly patients with a catheter as compared to elderly patients with an arteriovenous access were 1.54 (95% CI: 1.13-2.12) for all-cause mortality, 1.60 (95%: CI 0.62-4.19) for infection-related mortality and 1.67 (95% CI: 1.04-2.68) for cardiovascular mortality.

CONCLUSIONS

Especially, elderly haemodialysis patients with a catheter have an increased all-cause, infection-related and cardiovascular mortality risk as compared to patients with an arteriovenous access.

Chronic kidney disease stages 1-3 increase the risk of venous thrombosis

BACKGROUND

End-stage renal disease has been associated with venous thrombosis (VT). However, the risk of VT in the early stages of chronic kidney disease (CKD) has not yet been investigated. The aim of this study was to investigate whether CKD patients with stage 1-3 disease are at increased risk of VT.

METHODS

Eight thousand four hundred and ninety-five subjects were included in a prospective cohort study, in which renal function and albuminuria were assessed, starting in 1997-1998, and were followed for the occurrence of VT until 1 June 2007. CKD patients were staged according to the Kidney Disease Outcomes Quality Initiative guidelines, on the basis of 24-h urine albumin excretion and estimated glomerular filtration rates. Objectively verified symptomatic VT was considered to be the endpoint.

RESULTS

Of the 8495 subjects, 243 had CKD stage 1, 856 CKD stage 2, and 491 CKD stage 3. During a median follow-up period of 9.2 years, 128 individuals developed VT. The hazard ratios (HRs) for CKD stages 1, 2 and 3 were, respectively, 2.2 [95% confidence interval (CI) 0.9-5.1], 1.9 (95% CI 1.1-3.1) and 1.6 (95% CI 0.9-2.8) relative to those without CKD after adjustment for age, sex, body mass index, hypertension, diabetes, malignancy, and high-sensitivity C-reactive protein. Subjects with CKD stage 3 and albuminuria (≥ 30 mg d(-1)) had an adjusted HR of 3.0, and subjects with CKD stage 3 without albuminuria had an adjusted HR of 1.0.

CONCLUSIONS

CKD stages 1 and 2, and CKD stage 3 in the presence of albuminuria, are risk factors for VT. The risk of VT is more related to albuminuria than to impaired glomerular filtration rate.

Vitamin D status and clinical outcomes in incident dialysis patients: results from the NECOSAD study

BACKGROUND

The majority of dialysis patients suffer from vitamin D deficiency, which might contribute to an adverse health outcome. We aimed to elucidate whether European dialysis patients with low 25-hydroxyvitamin D (25(OH)D) levels are at increased risk of mortality and specific fatal events.

METHODS

This was a prospective cohort study of incident dialysis patients in the Netherlands (the NECOSAD). We selected all patients with measured 25(OH)D at 12 months after the start of dialysis, the baseline for our study. By Cox regression analyses, we assessed the impact of 25(OH)D levels on short-term (6 months of follow-up) as well as longer-term mortality (3 years of follow-up). Associations of 25(OH)D levels with cardiovascular and non-cardiovascular mortality were also determined.

RESULTS

The data from 762 patients (39% females, age 59 ± 15 years, 25(OH)D = 18 ± 11 ng/mL) were available. Fifty-one and 213 patients died during a follow-up of 6 months and 3 years, respectively. After adjustments for possible confounders, the hazard ratio (HR) (with 95% CI) for mortality was 2.0 (1.0-3.8) for short-term and 1.5 (1.0-2.1) for longer-term mortality when comparing patients with 25(OH)D levels ≤ 10 ng/mL with those presenting with 25(OH)D levels > 10 ng/mL. Adjusted HRs for cardiovascular mortality were 2.7 (1.1-6.5) and 1.7 (1.1-2.7) for short- and longer-term mortality, respectively. For non-cardiovascular mortality, we observed no relevant association overall. The impact of 25(OH)D levels on clinical events was modified by parathyroid hormone (PTH) status, with low 25(OH)D levels meaningfully affecting outcomes only in patients with PTH levels above the median of 123 pmol/L.

CONCLUSIONS

Vitamin D deficiency in dialysis patients is associated with an adverse health outcome, in particular with short-term cardiovascular mortality. Intervention studies are urgently needed to evaluate whether vitamin D supplementation improves health outcomes of dialysis patients.

Vitamin D deficiency is associated with sudden cardiac death, combined cardiovascular events, and mortality in haemodialysis patients

Aims

Dialysis patients experience an excess mortality, predominantly of sudden cardiac death (SCD). Accumulating evidence suggests a role of vitamin D for myocardial and overall health. This study investigated the impact of vitamin D status on cardiovascular outcomes and fatal infections in haemodialysis patients.

Methods and results

25-hydroxyvitamin D [25(OH)D] was measured in 1108 diabetic haemodialysis patients who participated in the German Diabetes and Dialysis Study and were followed up for a median of 4 years. By Cox regression analyses, we determined hazard ratios (HR) for pre-specified, adjudicated endpoints according to baseline 25(OH)D levels: SCD (n = 146), myocardial infarction (MI, n = 174), stroke (n = 89), cardiovascular events (CVE, n = 414), death due to heart failure (n = 37), fatal infection (n = 111), and all-cause mortality (n = 545). Patients had a mean age of 66 ± 8 years (54% male) and median 25(OH)D of 39 nmol/L (interquartile range: 28–55). Patients with severe vitamin D deficiency [25(OH)D of≤ 25 nmol/L] had a 3-fold higher risk of SCD compared with those with sufficient 25(OH)D levels >75 nmol/L [HR: 2.99, 95% confidence interval (CI): 1.39–6.40]. Furthermore, CVE and all-cause mortality were strongly increased (HR: 1.78, 95% CI: 1.18–2.69, and HR: 1.74, 95% CI: 1.22–2.47, respectively), all persisting in multivariate models. There were borderline non-significant associations with stroke and fatal infection while MI and deaths due to heart failure were not meaningfully affected.

Conclusion

Severe vitamin D deficiency was strongly associated with SCD, CVE, and mortality, and there were borderline associations with stroke and fatal infection. Whether vitamin D supplementation decreases adverse outcomes requires further evaluation.

Performance of the Cockcroft-Gault, MDRD, and new CKD-EPI formulas in relation to GFR, age, and body size

BACKGROUND AND OBJECTIVES

We compared the estimations of Cockcroft-Gault, Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations to a gold standard GFR measurement using (125)I-iothalamate, within strata of GFR, gender, age, body weight, and body mass index (BMI).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

For people who previously underwent a GFR measurement, bias, precision, and accuracies between measured and estimated kidney functions were calculated within strata of the variables. The relation between the absolute bias and the variables was tested with linear regression analysis.

RESULTS

Overall (n = 271, 44% male, mean measured GFR 72.6 ml/min per 1.73 m(2) [SD 30.4 ml/min per 1.73 m(2)]), mean bias was smallest for MDRD (P < 0.01). CKD-EPI had highest accuracy (P < 0.01 compared with Cockcroft-Gault), which did not differ from MDRD (P = 0.14). The absolute bias of all formulas was related to age. For MDRD and CKD-EPI, absolute bias was also related to the GFR; for Cockcroft-Gault, it was related to body weight and BMI as well. In all extreme subgroups, MDRD and CKD-EPI provided highest accuracies.

CONCLUSIONS

The absolute bias of all formulas is influenced by age; CKD-EPI and MDRD are also influenced by GFR. Cockcroft-Gault is additionally influenced by body weight and BMI. In general, CKD-EPI gives the best estimation of GFR, although its accuracy is close to that of the MDRD.

Mendelian randomization: use of genetics to enable causal inference in observational studies

The aim of aetiologic studies in epidemiology is to investigate whether factors are causally related to diseases and therefore become a potential target for therapeutic interventions. Mendelian randomization enables estimation of causal relationships in observational studies using genetic variants as instrumental variables. An instrumental variable is a variable that can be considered to mimic the coin toss in a randomized study. Given the random assignment of alleles in gamete formation, the use of genetic variants is an alternative method to control for confounding. This educational article describes the approach of Mendelian randomization, its underlying rationale and its necessary assumptions.

CCR5 deletion protects against inflammation-associated mortality in dialysis patients

The CC-chemokine receptor 5 (CCR5) is a receptor for various proinflammatory chemokines, and a deletion variant of the CCR5 gene (CCR5 Delta 32) leads to deficiency of the receptor. We hypothesized that CCR5 Delta 32 modulates inflammation-driven mortality in patients with ESRD. We studied the interaction between CCR5 genotype and levels of high-sensitivity C-reactive protein (hsCRP) in 603 incident dialysis patients from the multicenter, prospective NEtherlands COoperative Study on the Adequacy of Dialysis (NECOSAD) cohort. CCR5 genotype and hsCRP levels were both available for 413 patients. During 5 yr of follow-up, 170 patients died; 87 from cardiovascular causes. Compared with the reference group of patients who had the wild-type CCR5 genotype and hsCRP <or= 10 mg/L (n = 225), those carrying the deletion allele with hsCRP <or= 10 mg/L (n = 55) had similar mortality, and those carrying the wild-type genotype with hsCRP > 10 mg/L (n = 108) had an increased risk for mortality (HR: 1.82; 95% CI: 1.29 to 2.58). However, those carrying the deletion allele with hsCRP > 10 mg/L (n = 25) had a mortality rate similar to the reference group; this seemingly protective effect of the CCR5 deletion was even more pronounced for cardiovascular mortality. We replicated these findings in an independent Swedish cohort of 302 ESRD patients. In conclusion, the CCR5 Delta 32 polymorphism attenuates the adverse effects of inflammation on overall and cardiovascular mortality in ESRD.

Similar survival on automated peritoneal dialysis and continuous ambulatory peritoneal dialysis in a large prospective cohort

BACKGROUND AND OBJECTIVES

Automated peritoneal dialysis (APD) is increasingly used in comparison with continuous ambulatory peritoneal dialysis (CAPD). Although APD is expected to improve survival, convincing evidence of major advantages is lacking. The objective was to investigate whether overall mortality and technique failure of incident dialysis patients treated with APD are different from those treated with CAPD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Patients on APD or CAPD at 3 mo after start of dialysis were selected from a prospective multicenter cohort study in incident dialysis patients (NECOSAD). Overall mortality was studied with an intention-to-treat design; the event was death. Technique failure was studied with an as-treated design; the event was a switch of dialysis modality. Hazard ratios (HRs) were calculated with a follow-up of 5 yr. The HRs were adjusted for gender, age, primary kidney disease, comorbidity, residual GFR, urine production and plasma albumin at 3 mo after inclusion.

RESULTS

Eighty-seven APD and 562 CAPD patients were included. In the intention-to-treat analysis 154 CAPD and 21 APD patients died. The crude HR for overall mortality was 0.98 (95% CI: 0.62-1.54), the adjusted HR was 1.09. In the as-treated analysis 238 CAPD and 34 APD patients switched therapy, whereas 91 CAPD and 7 APD patients died. The crude HR for technique failure was 0.92 (95% CI: 0.64-1.31) and did not change after adjustment.

CONCLUSIONS

No difference was found in overall mortality and technique failure for APD compared with CAPD in incident dialysis patients.

Individual and joint expert judgments as reference standards in artifact detection

OBJECTIVE

To investigate the agreement among clinical experts in their judgments of monitoring data with respect to artifacts, and to examine the effect of reference standards that consist of individual and joint expert judgments on the performance of artifact filters.

DESIGN

Individual judgments of four physicians, a majority vote judgment, and a consensus judgment were obtained for 30 time series of three monitoring variables: mean arterial blood pressure (ABPm), central venous pressure (CVP), and heart rate (HR). The individual and joint judgments were used to tune three existing automated filtering methods and to evaluate the performance of the resulting filters.

MEASUREMENTS

The interrater agreement was calculated in terms of positive specific agreement (PSA). The performance of the artifact filters was quantified in terms of sensitivity and positive predictive value (PPV).

RESULTS

PSA values between 0.33 and 0.85 were observed among clinical experts in their selection of artifacts, with relatively high values for CVP data. Artifact filters developed using judgments of individual experts were found to moderately generalize to new time series and other experts; sensitivity values ranged from 0.40 to 0.60 for ABPm and HR filters (PPV: 0.57-0.84), and from 0.63 to 0.80 for CVP filters (PPV: 0.71-0.86). A higher performance value for the filters was found for the three variable types when joint judgments were used for tuning the filtering methods.

CONCLUSION

Given the disagreement among experts in their individual judgment of monitoring data with respect to artifacts, the use of joint reference standards obtained from multiple experts is recommended for development of automatic artifact filters.

Temporal abstraction for feature extraction: a comparative case study in prediction from intensive care monitoring data

OBJECTIVES

To compare two temporal abstraction procedures for the extraction of meta features from monitoring data. Feature extraction prior to predictive modeling is a common strategy in prediction from temporal data. A fundamental dilemma in this strategy, however, is the extent to which the extraction should be guided by domain knowledge, and to which extent it should be guided by the available data. The two temporal abstraction procedures compared in this case study differ in this respect.

METHODS AND MATERIAL

The first temporal abstraction procedure derives symbolic descriptions from the data that are predefined using existing concepts from the medical language. In the second procedure, a large space of numerical meta features is searched through to discover relevant features from the data. These procedures were applied to a prediction problem from intensive care monitoring data. The predictive value of the resulting meta features were compared, and based on each type of features, a class probability tree model was developed.

RESULTS

The numerical meta features extracted by the second procedure were found to be more informative than the symbolic meta features of the first procedure in the case study, and a superior predictive performance was observed for the associated tree model.

CONCLUSION

The findings indicate that for prediction from monitoring data, induction of numerical meta features from data is preferable to extraction of symbolic meta features using existing clinical concepts.

Prognostic Bayesian networks II: an application in the domain of cardiac surgery

A prognostic Bayesian network (PBN) is new type of prognostic model that implements a dynamic, process-oriented view on prognosis. In a companion article, the rationale of the PBN is described, and a dedicated learning procedure is presented. This article presents an application here of in the domain of cardiac surgery. A PBN is induced from clinical data of cardiac surgical patients using the proposed learning procedure; hospital mortality is used as outcome variable. The predictive performance of the PBN is evaluated on an independent test set, and results were compared to the performance of a network that was induced using a standard algorithm where candidate networks are selected using the minimal description length principle. The PBN is embedded in the prognostic system ProCarSur; a prototype of this system is presented. This application shows PBNs as a useful prognostic tool in medical processes. In addition, the article shows the added value of the PBN learning procedure.

Prognostic Bayesian networks I: rationale, learning procedure, and clinical use

Prognostic models are tools to predict the future outcome of disease and disease treatment, one of the fundamental tasks in clinical medicine. This article presents the prognostic Bayesian network (PBN) as a new type of prognostic model that builds on the Bayesian network methodology, and implements a dynamic, process-oriented view on prognosis. A PBN describes the mutual relationships between variables that come into play during subsequent stages of a care process and a clinical outcome. A dedicated procedure for inducing these networks from clinical data is presented. In this procedure, the network is composed of a collection of local supervised learning models that are recursively learned from the data. The procedure optimizes performance of the network's primary task, outcome prediction, and handles the fact that patients may drop out of the process in earlier stages. Furthermore, the article describes how PBNs can be applied to solve a number of information problems that are related to medical prognosis.

Bayesian networks for multivariate data analysis and prognostic modelling in cardiac surgery

Prognostic models are tools to predict the outcome of disease and disease treatment. These models are traditionally built with supervised machine learning techniques, and consider prognosis as a static, one-shot activity. This paper presents a new type of prognostic model that builds on the Bayesian network methodology that implements a dynamic, process-oriented view on prognosis. In contrast to traditional prognostic models, prognostic Bayesian networks explicate the scenarios that lead to disease outcomes, and can be used to update predictions when new information becomes available. A recursive data analysis strategy for inducing prognostic Bayesian networks from medical data is presented, and applied to data from the field of cardiac surgery. The resulting model outperformed a model that was constructed with off-the-shelf Bayesian network learning software, and had similar performance as class probability trees.

Comparison of two temporal abstraction procedures: a case study in prediction from monitoring data

This paper presents an empirical comparison of two temporal abstraction procedures, that were applied to derive predictive features for a prediction problem in intensive care medicine. The first procedure employs knowledge from practitioners to derive qualitative patterns of state changes; the second procedure searches through a large number of data summaries to discover those that have predictive value. The derived features were used to predict whether postsurgical patients would need mechanical ventilation longer then 24h. The data-driven temporal abstraction procedure was found to provide more informative predictors, resulting in better predictions.