Iron supplementation and mortality in incident dialysis patients: an observational study.

BACKGROUND: Studies on the association between iron supplementation and mortality in dialysis patients are rare and conflicting. METHODS: In our observational single-center cohort study (INVOR study) we prospectively studied 235 incident dialysis patients. Time-dependent Cox proportional hazards models using all measured laboratory values for up to 7.6 years were applied to study the association between iron supplementation and all-cause mortality, cardiovascular and sepsis-related mortality. Furthermore, the time-dependent association of ferritin levels with mortality in patients with normal C-reactive protein (CRP) levels (<0.5 mg/dL) and elevated CRP levels (≧0.5 mg/dL) was evaluated by using non-linear P-splines to allow flexible modeling of the association. RESULTS: One hundred and ninety-one (81.3%) patients received intravenous iron, 13 (5.5%) patients oral iron, whereas 31 (13.2%) patients were never supplemented with iron throughout the observation period. Eighty-two (35%) patients died during a median follow-up of 34 months, 38 patients due to cardiovascular events and 21 patients from sepsis. Baseline CRP levels were not different between patients with and without iron supplementation. However, baseline serum ferritin levels were lower in patients receiving iron during follow up (median 93 vs 251 ng/mL, p<0.001). Iron supplementation was associated with a significantly reduced all-cause mortality [HR (95%CI): 0.22 (0.08-0.58); p = 0.002] and a reduced cardiovascular and sepsis-related mortality [HR (95%CI): 0.31 (0.09-1.04); p = 0.06]. Increasing ferritin concentrations in patients with normal CRP were associated with a decreasing mortality, whereas in patients with elevated CRP values ferritin levels>800 ng/mL were linked with increased mortality. CONCLUSIONS: Iron supplementation is associated with reduced all-cause mortality in incident dialysis patients. While serum ferritin levels up to 800 ng/mL appear to be safe, higher ferritin levels are associated with increased mortality in the setting of concomitant inflammation.

Effect of different immunosuppressive drugs on immune cells from young and old healthy persons.

BACKGROUND: Life expectancy, as well as the average age of patients undergoing solid organ transplantation, increases constantly. Consequently, immunosuppressive therapy is no longer limited to young organ recipients. OBJECTIVE: Here, we investigate how different types of immunosuppressive therapy, namely the calcineurin inhibitors cyclosporin A and tacrolimus, as well as the mTOR inhibitor rapamycin, affect the function of immune cells in young and elderly persons. METHODS: Proliferation, cell viability, cytokine production (IL-2, IFN-γ), H2O2 production and telomere length of phytohemagglutinin (PHA)-stimulated human peripheral blood mononuclear cells (PBMCs) of young (n = 13; median age 27 years) and old (n = 19; median age 71 years) healthy donors were analyzed. RESULTS: The inhibition of proliferation was dampened in PBMCs from elderly donors, especially after incubation with rapamycin. All three immunosuppressive drugs inhibited the production of IL-2 equally well, whereas the production of IFN-γ was less well inhibited by rapamycin. Both calcineurin inhibitors increased H2O2 concentrations after stimulation with PHA and led to a shortening of telomeres in PBMCs from young and old individuals. Rapamycin had only minor effects on H2O2 production and telomere length. CONCLUSION: Our results demonstrate that the effects of immunosuppressive drugs on PBMCs differ between young and elderly persons. Calcineurin inhibitors compared to rapamycin have a more pronounced prosenescence effect. These data indicate that specific treatment regimens for the elderly might therefore be considered.

Comparison and evaluation of cardiac biomarkers in patients with intermittent claudication: results from the CAVASIC study.

BACKGROUND: Plasma concentrations of the peptides midregional proadrenomedullin (MR-proADM), midregional proatrial natriuretic peptide (MR-proANP), and C-terminal endothelin-1 precursor fragment (CT-proET-1) are increased in various cardiovascular conditions. However, there is limited information about the association and comparative performance of these peptides in peripheral arterial disease (PAD). METHODS: The associations of MR-proADM, MR-proANP, and CT-proET-1 plasma concentrations with symptomatic PAD were investigated in the CAVASIC (Cardiovascular Disease in Intermittent Claudication) Study. Study participants were a male cohort of 238 patients with a diagnosis of intermittent claudication (IC) and 245 age- and diabetes-matched controls. Results were compared to those for N-terminal pro-B-type natriuretic peptide (NT-proBNP). RESULTS: Each increase of MR-proADM, MR-proANP, and CT-proET-1 by 1 SD was significantly associated with symptomatic PAD: odds ratio (OR) = 1.78 (95% CI, 1.41-2.25, P < 0.001), OR = 1.32 (95% CI, 1.06-1.66, P = 0.014), and OR = 1.80 (95% CI, 1.43-2.28, P < 0.001), respectively. The association remained significant for all 3 markers after additional adjustment for log C-reactive protein, serum creatinine, HDL cholesterol, and current smoking. When one adjusts for log NT-proBNP and excluding individuals with prevalent cardiovascular disease, MR-proADM and CT-proET-1 still predicted symptomatic PAD. Extended adjustment models including MR-proADM or CT-proET-1 showed significantly improved model fits compared to models including classical cardiac risk factors or NT-proBNP and led to significant reclassification (P < 0.05). CONCLUSIONS: This study in a male cohort of patients with IC and age- and diabetes-matched controls indicates a significant association of high MR-proADM, MR-proANP, and CT-proET-1 concentrations with PAD. MR-proADM and CT-proET-1 provide additive information in comparison to NT-proBNP. Moreover, MR-proADM and CT-proET-1 significantly predict PAD in those patients and controls free from prevalent CVD.

Visualizing interaction effects: a proposal for presentation and interpretation.

OBJECTIVE: Interaction terms are often included in regression models to test whether the impact of one variable on the outcome is modified by another variable. However, the interpretation of these models is often not clear. We propose several graphical presentations and corresponding statistical tests alleviating the interpretation of interaction effects. STUDY DESIGN AND SETTING: We implemented functions in the statistical program R that can be used on interaction terms in linear, logistic, and Cox Proportional Hazards models. Survival data were simulated to show the functionalities of our proposed graphical visualization methods. RESULTS: The mutual modifying effect of the interaction term is grasped by our presented figures and methods: the combined effect of both continuous variables is shown by a two-dimensional surface mimicking a 3D-Plot. Furthermore, significance regions were calculated for the two variables involved in the interaction term, answering the question for which values of one variable the effect of the other variable significantly differs from zero and vice versa. CONCLUSION: We propose several graphical visualization methods to ease the interpretation of interaction effects making arbitrary categorizations unnecessary. With these approaches, researchers and clinicians are equipped with the necessary information to assess the clinical relevance and implications of interaction effects.

Coumarins and survival in incident dialysis patients.

BACKGROUND: The benefit and risk of oral anticoagulation in dialysis patients are debated controversially. METHODS: We prospectively followed 235 dialysis patients of the INVOR Study (Study of Incident Dialysis Patients in Vorarlberg) for up to 7 years and analysed the prevalence and incidence of atrial fibrillation (AF) and the impact of coumarin therapy on survival. Oral anticoagulation was monitored frequently. RESULTS: A total of 748 person-years were recorded with a median follow-up of 2.84 years. Twelve patients (5.1%) had AF at the start of dialysis. During follow-up, 40 patients (17.0%) developed AF, representing an incidence of 5.85 per 100 person-years. AF was positively associated with mortality (P = 0.004). Forty-six (19.6%) of the 235 patients were treated with coumarins. The majority (93.7%) had a clear indication for oral anticoagulation. In 65% of our patients, AF was the indication for coumarins. Patients without coumarins and without AF represented our reference group. The mortality risk of the coumarin-treated patients with AF or an alternative indication for coumarins was slightly lower compared to the reference group [hazard ratio (HR) 95% confidence interval (CI): 0.80 (0.28-2.29), P = 0.679 and 0.42 (0.16-1.10), P = 0.078, respectively]. No patient under sufficient oral anticoagulation experienced a stroke or a fatal bleeding event. Patients with AF and a contraindication for coumarins had a significantly higher mortality risk compared to the reference group [HR (95% CI): 3.90 (2.16-7.04), P < 0.001]. CONCLUSIONS: Our data suggest that coumarins might be less harmful than previously anticipated when clearly indicated and closely monitored.

Interaction of time-varying albumin and phosphorus on mortality in incident dialysis patients.

BACKGROUND AND OBJECTIVES: Hypoalbuminemia and hyperphosphatemia have been shown to be strong predictors of mortality in dialysis patients that might not be independent from each other. We prospectively investigated the relationship and interaction between serum albumin and phosphorus with all-cause mortality in an inception cohort of incident dialysis patients. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: We followed 235 incident dialysis patients in a prospective single-center cohort study (INVOR study) applying a time-dependent Cox proportional hazards model using all measured laboratory values (2887 albumin and 10306 phosphorus values). RESULTS: Eighty-two patients (35%) died during a median follow-up of 35.1 months. Albumin was inversely associated with mortality (hazard ratio [95% confidence interval]: 0.23 [0.14 to 0.36]; P < 0.001), whereas higher phosphorus concentrations showed a trend to an increasing risk for mortality (hazard ratio 1.57 [95% confidence interval 0.97 to 2.54]; P = 0.07). Importantly, we observed a significant interaction between albumin and phosphorus (P = 0.01). The lowest risk was found with concurrent low phosphorus and high albumin values, whereas risk was increased with either concurrent low phosphorus and low albumin values or high phosphorus and high albumin values. CONCLUSIONS: In incident dialysis patients the associations of serum phosphorus and albumin concentrations with mortality are modified by each other over time. Phosphorus-lowering interventions that concomitantly can cause a fall in serum albumin level may be harmful and warrant additional studies. If confirmed, epidemiologic studies and therapeutic guidelines aiming for target values should consider this interplay.

Association of HbA1c values with mortality and cardiovascular events in diabetic dialysis patients. The INVOR study and review of the literature.

BACKGROUND: Improved glycemic control reduces complications in patients with diabetes mellitus (DM). However, it is discussed controversially whether patients with diabetes mellitus and end-stage renal disease benefit from strict glycemic control. METHODS: We followed 78 patients with DM initiating dialysis treatment of the region of Vorarlberg in a prospective cohort study applying a time-dependent Cox regression analysis using all measured laboratory values for up to more than seven years. This resulted in 880 HbA(1c) measurements (with one measurement every 3.16 patient months on average) during the entire observation period. Non-linear P-splines were used to allow flexible modeling of the association with mortality and cardiovascular disease (CVD) events. RESULTS: We observed a decreased mortality risk with increasing HbA(1c) values (HR = 0.72 per 1% increase, p = 0.024). Adjustment for age and sex and additional adjustment for other CVD risk factors only slightly attenuated the association (HR = 0.71, p = 0.044). A non-linear P-spline showed that the association did not follow a fully linear pattern with a highly significant non-linear component (p = 0.001) with an increased risk of all-cause mortality for HbA(1c) values up to 6-7%. Causes of death were associated with HbA(1c) values. The risk for CVD events, however, increased with increasing HbA(1c) values (HR = 1.24 per 1% increase, p = 0.048) but vanished after extended adjustments. CONCLUSIONS: This study considered the entire information collected on HbA(1c) over a period of more than seven years. Besides the methodological advantages our data indicate a significant inverse association between HbA(1c) levels and all-cause mortality. However, for CVD events no significant association could be found.

The association of mid-regional pro-adrenomedullin and mid-regional pro-atrial natriuretic peptide with mortality in an incident dialysis cohort.

High levels of the plasma peptides mid-regional pro-adrenomedullin (MR-proADM) and mid-regional pro-atrial natriuretic peptide (MR-proANP) are associated with clinical outcomes in the general population. Data in patients with chronic kidney disease are sparse. We therefore investigated the association of MR-proANP and MR-proADM levels with all-cause and cardiovascular (CV) mortality, CV events and peripheral arterial disease in 201 incident dialysis patients of the INVOR-Study prospectively followed for a period of up to more than 7 years. The overall mortality rate was 43%, thereof 43% due to CV events. Both baseline MR-proANP and MR-proADM were associated with higher risk of all-cause (HR = 1.44, p = 0.001 and HR = 1.32, p = 0.002, respectively) and CV mortality (HR = 1.75, p<0.001 and HR = 1.41, p = 0.007, respectively) after adjustment for age, sex, previous CV events, diabetes mellitus and time-dependent type of renal replacement therapy. We then stratified patients in high risk (both peptides in the upper tertile), intermediate risk (only one of the two peptides in the upper tertile) and low risk (none in the upper tertile). Although demographic, clinical and laboratory variables were similar among the intermediate and high risk group, to be with both parameters in the upper tertile was associated with a 3-fold higher risk for all-cause (HR = 2.87, p<0.001) and CV mortality (HR = 3.58, p = 0.001). In summary, among incident dialysis patients MR-proANP and MR-proADM were shown to be associated with all-cause and CV mortality, with the highest risk when both parameters were in the upper tertiles.

Sex-specific association of time-varying haemoglobin values with mortality in incident dialysis patients.

BACKGROUND: Previous studies in dialysis patients showed an association between haemoglobin levels and all-cause mortality, however, without addressing sex differences. METHODS: We followed up 235 incident dialysis patients of the region of Vorarlberg in a prospective cohort study applying a time-dependent Cox regression analysis using all the measured laboratory values for up to more than 7 years. In total, 12 242 haemoglobin measurements with a median of 47 (range 3-270) per patient were available to evaluate the impact of haemoglobin levels and their variability on all-cause mortality in a sex-stratified analysis. Non-linear P-splines were used to allow a flexible modelling of the association with mortality. RESULTS: We observed an inverse relationship between the increasing haemoglobin values and the decreasing risk of mortality. The linear component of the non-linear spline was highly significant for both men (P = 0.00005) and women (P = 0.0000000052). The non-linear component was also significant but less pronounced than the linear component. The inverse relationship was clear to see haemoglobin levels of up to 12-13 g/L in women, which reached a plateau for the higher values of haemoglobin. For men, an inverse trend was observed but clearly attenuated when compared to women. After adjustment for additional parameters of inflammation and malnutrition as well as diabetes, the linear component was more significant in women (P = 0.0018) than in men (P = 0.023). CONCLUSIONS: This study applied for the first time a time-dependent Cox regression analysis over a long-term observation period of several years using all available measurements. Besides the methodological advantages, our data indicate a sex-specific linear as well as non-linear effect of haemoglobin levels on all-cause mortality, which was markedly more pronounced in women.

Uric acid as a risk factor for progression of non-diabetic chronic kidney disease? The Mild to Moderate Kidney Disease (MMKD) Study.

The kidney is one of the organs most prominently affected by aging. This can be seen by a loss of renal mass which is caused by a decrease in the number of nephrons resulting in hyperfiltration, hypertrophy and elevations in glomerular pressure. The factors influencing aging of the kidney are not fully elucidated. Epidemiological, experimental and interventional studies resulted in inconsistent results and have not firmly established whether uric acid levels affect progression of Chronic Kidney Disease (CKD). Therefore, we analyzed whether uric acid levels predict the progression of CKD in the Mild to Moderate Kidney Disease Study comprising at baseline 227 Caucasian patients aged 18-65 years with primary non-diabetic CKD of various degrees of renal impairment. Of them, 177 completed a prospective follow-up of 7 years. Primary endpoint was progression of CKD defined as doubling of baseline serum creatinine and/or terminal renal failure. Patients who reached a progression endpoint (n =6 5) were significantly older, had higher baseline serum creatinine and protein excretion rates as well as lower Glomerular Filtration Rate (GFR). Uric acid levels were only higher in patients with progression of disease when patients with uric acid-lowering drugs were excluded from the analysis. Cox regression analysis revealed that increasing uric acid levels predict disease progression only when the analysis was not adjusted for baseline kidney function parameters. As soon as we adjusted the analysis for GFR and proteinuria this association completely vanished. In summary, our prospective 7 year follow-up study in patients with non-diabetic primary CKD did not support uric acid as an independent predictor for CKD progression.