No independent association of serum phosphorus with risk for death or progression to end-stage renal disease in a large screen for chronic kidney disease

Relationship between serum phosphorus and mortality in non-dialysis chronic kidney disease patients: evidence from NHANES 2001-2018

BACKGROUND

Hyperphosphatemia is common in chronic kidney disease (CKD), associated with higher mortality in dialysis patients. Its impact in non-dialysis patients, especially those with preserved kidney function, remains uncertain.

METHODS

A prospective cohort study was conducted using data from the National Health and Nutrition Examination Survey (2001-2008). Serum phosphorus was analyzed as a continuous variable, or categorized into three groups: < 3.5 mg/dL, 3.5 to < 4.5 mg/dL, and ≥ 4.5 mg/dL. Cox proportional hazards models were used to analyze the association between phosphorus with all-cause and cardiovascular disease (CVD) mortality, with or without adjustment for age, sex, race, hemoglobin, estimated glomerular filtration rate (eGFR), serum albumin, serum calcium, 25(OH)D, obesity, hypertension, diabetes, and CVD.

RESULTS

A total of 7694 participants were included in the analysis, representing 28 million CKD patients in the United States. During mean 92 months of follow up, 2708 all-cause deaths (including 969 CVD deaths) were observed. Per 1 mg/dL increase in phosphorus was associated with a 13% and 24% increased risk of all-cause mortality (hazard ratio [HR], 1.13; 95%CI, 1.02-1.24) and CVD mortality (HR, 1.24; 95%CI, 1.07-1.45), respectively. Compared with the < 3.5 mg/dL, phosphorus ≥ 4.5 mg/dL was associated with a 28% and 57% increased risk of all-cause mortality (HR, 1.28; 95%CI, 1.05-1.55) and CVD mortality (HR, 1.57; 95CI, 1.19-2.08), respectively. In participants with eGFR < 60 ml/min/1.73m2, elevated phosphorus (≥ 4.5 mg/ dL) were significantly associated with increased risk of all-cause mortality (HR, 1.36; 95%CI, 1.07-1.72). No significant association was observed in eGFR ≥ 60 ml/min/1.73m2 group (HR, 1.31; 95%CI, 0.86-1.99). This correlation does not differ significantly between subgroups defined by eGFR level (P for interaction = 0.889).

CONCLUSION

Serum phosphorus above 4.5 mg/dL is significantly associated with a 28% and 57% increased risk of all-cause and CVD death in non-dialysis CKD patients, respectively. This relationship still demonstrated in patients with eGFR < 60 ml/min/1.73m2. However, for population with eGFR ≥ 60 ml/min/1.73m2, further verification is needed.

The association of normal-range serum phosphorus with immunoglobulin A nephropathy progression: a retrospective cohort study

PURPOSE

The relationship between serum phosphorus and immunoglobulin A (IgA) nephropathy progression remains uncertain, especially normal-range serum phosphorus. Therefore, we herein examined the relationship between the normal-range serum phosphorus and the progression of IgA nephropathy.

METHODS

One hundred sixty-two patients with primary IgA nephropathy were divided into three groups according to tertiles of baseline serum phosphorus (first tertile: 0.73-1.04 mmol/L; second tertile: 1.04-1.21 mmol/L; third tertile: 1.21-1.60 mmol/L). Estimated glomerular filtration rate (eGFR) was calculated using the chronic kidney disease epidemiology collaboration. The composite outcome was defined as a decrease of at least 50% in eGFR from baseline or end-stage kidney disease (ESKD). The association of serum phosphorus with IgA nephropathy progression was estimated using Cox proportional hazards models, adjusting for potential confounders.

RESULTS

During a median 16 month follow-up period, 15 patients reached a composite outcome. In the crude Cox proportional hazard model, baseline serum phosphorus as a continuous variable was associated with increased risk for adverse renal outcomes [hazard ratio (HR) = 63.510, 95% confidence interval (CI) = 3.953-1020.284, P = 0.003], and the high tertile of serum phosphorus group had an increased risk of the composite outcome by using the low tertile group as the reference (HR = 11.895, 95% CI = 1.522-92.993, P = 0.018). After adjustment for traditional risk factors, the high tertile of serum phosphorus group was significantly related to IgA nephropathy progression compared with the low tertile group (HR = 9.424, 95% CI = 1.019-87.165, P = 0.048).

CONCLUSIONS

Relatively higher serum phosphorus levels within the normal range were significantly associated with the progression of IgA nephropathy.

Association of mineral and bone biomarkers with adverse cardiovascular outcomes and mortality in the German Chronic Kidney Disease (GCKD) cohort

Mineral and bone disorder (MBD) in chronic kidney disease (CKD) is tightly linked to cardiovascular disease (CVD). In this study, we aimed to compare the prognostic value of nine MBD biomarkers to determine those associated best with adverse cardiovascular (CV) outcomes and mortality. In 5 217 participants of the German CKD (GCKD) study enrolled with an estimated glomerular filtration rate (eGFR) between 30-60 mL·min-1 per 1.73 m2 or overt proteinuria, serum osteoprotegerin (OPG), C-terminal fibroblast growth factor-23 (FGF23), intact parathyroid hormone (iPTH), bone alkaline phosphatase (BAP), cross-linked C-telopeptide of type 1 collagen (CTX1), procollagen 1 intact N-terminal propeptide (P1NP), phosphate, calcium, and 25-OH vitamin D were measured at baseline. Participants with missing values among these parameters (n = 971) were excluded, leaving a total of 4 246 participants for analysis. During a median follow-up of 6.5 years, 387 non-CV deaths, 173 CV deaths, 645 nonfatal major adverse CV events (MACEs) and 368 hospitalizations for congestive heart failure (CHF) were observed. OPG and FGF23 were associated with all outcomes, with the highest hazard ratios (HRs) for OPG. In the final Cox regression model, adjusted for CV risk factors, including kidney function and all other investigated biomarkers, each standard deviation increase in OPG was associated with non-CV death (HR 1.76, 95% CI: 1.35-2.30), CV death (HR 2.18, 95% CI: 1.50-3.16), MACE (HR 1.38, 95% CI: 1.12-1.71) and hospitalization for CHF (HR 2.05, 95% CI: 1.56-2.69). Out of the nine biomarkers examined, stratification based on serum OPG best identified the CKD patients who were at the highest risk for any adverse CV outcome and mortality.

The Usefulness of Calcium/Magnesium Ratio in the Risk Stratification of Early Onset of Renal Replacement Therapy

Background: A growing number of studies have reported a close relationship between high serum calcium (Ca)/low serum magnesium (Mg) and vascular calcification. Endothelial dysfunction and vascular inflammation seem plausible risk factors for the enhanced progression of kidney disease. The aim of this study was to evaluate the role of the Ca/Mg ratio as a predictor of the early onset of renal replacement therapy (RRT). Methods: This was a prospective study conducted in an outpatient low-clearance nephrology clinic, enrolling 693 patients with stages 4−5 of CKD. Patients were divided into two groups according to the start of renal replacement therapy (RRT). Results: The kidney’s survival at 120 months was 60% for a Ca−Mg ratio < 6 and 40% for a Ca−Mg ratio ≥ 6 (p = 0.000). Patients who started RRT had lower levels of Hb, Ca, Mg, albumin, and cholesterol and higher values of phosphorus, the Ca/Mg ratio, and PTH. High values of phosphorus and the Ca/Mg ratio and low levels of Mg and GFR were independent predictors of entry into RRT. A high Ca/Mg ratio, high phosphorus levels, and low levels of GFR were associated with a cumulative risk for initiation of RRT. Conclusions: In our population, the Ca/Mg ratio is an independent predictive factor for the initiation of a depurative technique.

CKD-MBD Biomarkers and CKD Progression: an Analysis by the Joint Model

BACKGROUND

Biomarkers of the CKD- Bone Mineral Disorder (CKD-BMD have been implicated in CKD progression in follow up studies focusing on single measurements of individual biomarkers made at baseline only. The simultaneous relationship between the time trend of these biomarkers over the course of CKD and renal outcomes has never been tested.

METHODS

We applied the Joint Model (JM) to investigate the longitudinal relationship between repeated measurements of CKD-MBD biomarkers and a combined renal endpoint (eGFR reduction >30%, dialysis or transplantation) in 729 stage 2-5 CKD patients over a 36 months follow up.

RESULTS

In the survival sub-model of the JM the longitudinal series of PTH values was directly and independently related to the risk of renal events [HR (1ln PTH) = 2.0 (from 1.5 to 2.8), p<0.001)] and this was also true for repeated measurements of serum phosphate [HR(1mg/dl) = 1.3924 (from 1.1459 to 1.6918), p = 0.001], serum calcium [HR(1mg/dl) = 0.7487 (from 0.5843 to 0.9593), p = 0.022], baseline FGF23 [HR(1pg/ml) = 1.001 (from 1.00 to 1.002), p = 0.045] and 1,25 dihydroxy Vitamin D [HR (1pg/ml) = 0.9796 (from 0.9652 to 0.9942), p = 0.006].

CONCLUSION

Repeated measurements of serum PTH, calcium and phosphate as well as baseline FGF23 and 1,25 dihydroxy vitamin D are independently related with the progression to kidney failure in a cohort of stage 2-5 CKD patients. This longitudinal study generates the hypothesis that interventions at multiple levels on BMD biomarkers can mitigate renal function loss in this population.

Association between Serum Inorganic Phosphorus Levels and Adverse Outcomes in Chronic Kidney Disease: The Fukushima CKD Cohort Study

Objective Although an association between serum inorganic phosphorus levels and a poor prognosis has been noted in dialysis patients, these associations have been insufficiently reported in non-dialysis-dependent chronic kidney disease (NDD-CKD) patients. This study attempted to determine the association between serum inorganic phosphorus levels and adverse outcomes in Japanese NDD-CKD patients. Methods We investigated the relationships between serum inorganic phosphorus levels and adverse outcomes, such as kidney events, cardiovascular events, and all-cause death, in Japanese NDD-CKD patients using longitudinal data from the Fukushima CKD Cohort Study with a median follow-up period of 2.8 years. The study evaluated 822 patients with NDD-CKD enrolled between June 2012 and July 2014. A kidney event was defined as a combination of doubling of the baseline serum creatinine or end-stage renal disease. Cox regression was performed to analyze the relationships of the quartile of the serum inorganic phosphorus with kidney events, cardiovascular events, and all-cause death. Results The frequency of kidney events per 1,000 person-years exhibited a U-shaped distribution based on serum inorganic phosphorus levels, with these levels not significantly associated with an increased risk of cardiovascular events and all-cause death. A multivariable Cox regression analysis showed an increased risk of kidney events for the highest quartile of the serum inorganic phosphorus levels (≥3.7 mg/dL) versus the second quartile (2.9-3.2 mg/dL, hazard ratio, 3.30; 95% confidence interval, 1.50-7.28; p=0.003). There were no significant associations between the serum calcium levels and adverse outcomes. Conclusion Serum inorganic phosphorus levels were associated with an increased risk of CKD progression in Japanese NDD-CKD patients.

Serum Phosphorus and Albumin in Patients Undergoing Peritoneal Dialysis: Interaction and Association With Mortality

Hyperphosphatemia and hypoalbuminemia confer worse clinical outcomes, whether these risk factors interact to predispose to mortality is unclear. In this prospective cohort study, 2,118 patients undergoing incident continuous ambulatory peritoneal dialysis (CAPD) were enrolled and categorized into four groups based on the changing point regarding mortality at 1.5 mmol/L for serum phosphorus and 35 g/L for serum albumin. Risks of all-cause and cardiovascular mortality were examined independently and interactively in overall and subgroups. There was no association between serum phosphorus with all-cause and cardiovascular mortality, but significant interactions (p = 0.02) between phosphorus and albumin existed in overall population. Patients in subgroup with high phosphorus and low albumin were at greater risk of all-cause (HR 1.95, 95%CI 1.27–2.98, p = 0.002) but not cardiovascular mortality (HR 0.37, 95%CI 0.10–1.33, p = 0.13), as compared to those with low phosphorus and high albumin. In contrast, patients with both low parameters had a higher risk of all-cause (HR 1.75, 95%CI 1.22–2.50, p = 0.002) and cardiovascular mortality (HR 1.92, 95%CI 1.07–3.45, p = 0.03). Notably, an elevated risk of both all-cause and cardiovascular mortality was observed in those with low serum albumin, irrespective of phosphorus levels, suggesting low albumin may be useful to identify a higher-risk subgroup of patients undergoing CAPD with different serum phosphorus levels.

Serum phosphate and chronic kidney and cardiovascular disease: Phosphorus potential implications in general population

It has already been established that in end-stage renal disease, hyperphosphatemia causes soft tissue calcification including vascular calcifications. It has also been supported that there is a connection between increased serum phosphate and morbidity in subjects, who suffer from renal disease. However, studies in these populations conferred mixed results. Several warnings are included in the role of serum phosphorus on cardiovascular disease in normal populations. Homeostasis of serum phosphate is obtained by the cooperation between regulatory hormones, cellular receptors and bone metabolic factors. There is the probability that one or more phosphate regulatory factors, rather than phosphate directly, may be responsible for observed associations with calcification and cardiovascular events in normal populations. Experimental studies have shown that the restriction of dietary phosphate prevents the progression of kidney dysfunction, although high dietary phosphate aggravates the renal function. In the current review, we discuss the role of serum phosphorus on progression of renal dysfunction and cardiovascular outcomes in chronic kidney disease patients and its involvement in important health risks in the general population.

Serum phosphorus and calcium levels, and kidney disease progression in immunoglobulin A nephropathy

BACKGROUND

Disorders of calcium and phosphorus metabolism have been reported to be associated with all-cause and cardiovascular mortality in patients requiring long-term dialysis therapy. However, its role in disease progression is not well established in patients without dialysis, especially in immunoglobulin A (IgA) nephropathy. We aim to evaluate the association of serum phosphorus and calcium and progression of IgA nephropathy.

METHODS

We assessed 2567 patients with IgA nephropathy at the First Affiliated Hospital, College of Medicine, Zhejiang University. Serum phosphorus and calcium were collected at the time of kidney biopsy and at each visit. The associations of serum phosphorus and serum calcium with composite kidney disease progression events, defined as 50% estimated glomerular filtration rate (eGFR) decline and kidney failure, were examined using Cox models and restricted cubic splines.

RESULTS

During a median follow-up of 31.9 months, 248 (10%) patients reached composite kidney disease progression events. A linear relationship was observed between serum phosphorus and composite kidney disease progression events. With higher levels of phosphorus, the risk of kidney disease progression events increased {hazard ratio [HR] 3.54 [95% confidence interval (CI) 1.37-9.12]; P = 0.009}. Compared with the first quartile group, the HR of kidney disease progression events was 1.66 (95% CI 0.91-301) for the second quartile, 1.67 (95% CI 0.91-3.08) for the third and 2.62 (95% CI 1.44-4.77) for the fourth (P for trend = 0.002). The association between serum phosphorus and kidney disease progression was detectable [HR 8.94 (95% CI 2.33-34.21); P = 0.001] within the subgroup with eGFR <60 mL/min/1.73 m2 but not among patients with eGFR ≥60 mL/min/1.73 m2 [HR 0.87 (95% CI 0.17-4.44); P = 0.87]. After adjustment for traditional risk factors, a higher level of serum calcium was not associated with kidney disease progression events [HR 0.33 (95% CI 0.10-1.09)].

CONCLUSIONS

Higher serum phosphorus rather than serum calcium was independently associated with kidney disease progression in IgA nephropathy.

Influence of vitamin D treatment on functional expression of drug disposition pathways in human kidney proximal tubule cells during simulated uremia

Effects of cholecalciferol (VitD₃) and calcitriol (1,25-VitD₃), on the expression and function of major vitamin D metabolizing enzymes (cytochrome P450 [CYP]2R1, CYP24A1) and select drug transport pathways (ABCB1/P-gp, SLCO4C1/OATP4C1) were evaluated in human kidney proximal tubule epithelial cells (hPTECs) under normal and uraemic serum conditions.hPTECs were incubated with 10% normal or uraemic serum for 24 h followed by treatment with 2% ethanol vehicle, or 100 and 240 nM doses of VitD₃, or 1,25-VitD₃ for 6 days. The effects of treatment on mRNA and protein expression and functional activity of select CYP enzymes and transporters were assessedUnder uraemic serum, treatment with 1,25-VitD₃ resulted in increased mRNA but decreased protein expression of CYP2R1. Activity of CYP2R1 was not influenced by serum or VitD analogues. CYP24A1 expression was increased with 1,25-VitD₃ under normal as well as uraemic serum, although to a lesser extent. ABCB1/P-gp mRNA expression increased under normal and uraemic serum, with exposure to 1,25-VitD₃. SLCO4C1/OATP4C1 exhibited increased mRNA but decreased protein expression, under uraemic serum + 1,25-VitD₃. Functional assessments of transport showed no changes regardless of exposure to serum or 1,25-VitD₃.Key findings indicate that uraemic serum and VitD treatment led to differential effects on the functional expression of CYPs and transporters in hPTECs.

Dietary Phosphorus as a Marker of Mineral Metabolism and Progression of Diabetic Kidney Disease

Phosphorus is an essential nutrient that is critically important in the control of cell and tissue function and body homeostasis. Phosphorus excess may result in severe adverse medical consequences. The most apparent is an impact on cardiovascular (CV) disease, mainly through the ability of phosphate to change the phenotype of vascular smooth muscle cells and its contribution to pathologic vascular, valvular and other soft tissue calcification. Chronic kidney disease (CKD) is the most prevalent chronic disease manifesting with the persistent derangement of phosphate homeostasis. Diabetes and resulting diabetic kidney disease (DKD) remain the leading causes of CKD and end-stage kidney disease (ESRD) worldwide. Mineral and bone disorders of CKD (CKD-MBD), profound derangement of mineral metabolism, develop in the course of the disease and adversely impact on bone health and the CV system. In this review we aimed to discuss the data concerning CKD-MBD in patients with diabetes and to analyze the possible link between hyperphosphatemia, certain biomarkers of CKD-MBD and high dietary phosphate intake on prognosis in patients with diabetes and DKD. We also attempted to clarify if hyperphosphatemia and high phosphorus intake may impact the onset and progression of DKD. Careful analysis of the available literature brings us to the conclusion that, as for today, no clear recommendations based on the firm clinical data can be provided in terms of phosphorus intake aiming to prevent the incidence or progression of diabetic kidney disease.

Joint Longitudinal Low Calcium High Phosphorus Trajectory Associates with Accelerated Progression, Acute Coronary Syndrome and Mortality in Chronic Kidney Disease

The effects of long-term disturbance of the mineral metabolism on patients with chronic kidney disease (CKD) are unclear. We investigated whether the longitudinal Ca-P (joint calcium and phosphorus) trajectories are associated with incident end-stage renal disease (ESRD), acute coronary syndrome (ACS), and all-cause mortality in patients with CKD. We conducted a prospective cohort study by using data from a 13-year multidisciplinary pre-ESRD care registry. The final study population consisted of 4,237 CKD patients aged 20–90 years with data gathered from 2003 to 2015. Individuals’ Ca-P trajectories were defined using group-based multi-trajectory modeling into three distinct patterns: reference, moderately abnormal, and severely abnormal. Times to ESRD, ACS, and death were analyzed using multiple Cox regression. Compared with those with a “reference” Ca-P trajectory, the adjusted hazard ratios (aHRs) (95% confidence interval [CI]) for incidental ESRD were 5.92 (4.71–7.44) and 15.20 (11.85–19.50) for “moderately abnormal” and “severely abnormal” Ca-P trajectories, respectively. The corresponding aHRs for ACS were 1.94 (1.49–2.52) and 3.18 (2.30–4.39), and for all-cause mortality, they were 1.88 (1.64–2.16) and 2.46 (2.05–2.96) for “moderately abnormal” and “severely abnormal” Ca-P trajectories, respectively. For outcomes of progression to ESRD, the detrimental effects of abnormal Ca-P trajectories were more substantial in patients with CKD stage 3 than those with CKD stage 4 or 5 (p-value for interaction < 0.001). Future studies should validate reliable longitudinal cut-offs of serum phosphorus and consider the “lowering phosphorus— the lower the better, the earlier the better” approach to phosphorus control in CKD.

Renal resistive index in chronic kidney disease patients: Possible determinants and risk profile

BACKGROUND

High ultrasound renal resistive index (RI) predicts poor cardiorenal outcomes in chronic kidney disease (CKD) and has recently emerged as a marker of nephroprotective drugs response. Thus, having a risk profile of CKD patients with abnormal RI may be relevant for the clinicians.

METHODS

Consecutive patients referred to our non-dialysis CKD clinic from 01/01/2016 to 01/12/2016, were evaluated by clinical and ultrasound analysis. Inclusion criteria were age >18 years and presence of CKD defined as estimated glomerular filtration rate (eGFR)<60 mL/min/1.73m2 and/or proteinuria>0.150g/24h. Renal artery stenosis, solitary kidney, acute kidney injury were the main exclusion criteria. RI value was the mean of three measures in segmental arteries in each kidney. Univariate analysis was performed to evaluate associations between continuous RI and clinical variables. Multivariate linear regression analysis, based on stepwise method with an elimination criterion of p<0.10, was used to assess the independent correlates of RI as continuous variable.

RESULTS

We studied 73 patients (69.9% men). Mean RI was 0.67±0.09. Frequencies of diabetes and cardiovascular disease (CVD) were 19.2% and 20.6% and median eGFR 54.1 [30.0-84.6] mL/min/1.73m2. From low (<0.65) to intermediate (0.65-0.70) to high (>0.70) RI categories, eGFR and haemoglobin levels were decreased while diabetes, cardiovascular disease (CVD), phosphate and smokers were higher. At univariate analysis, RI was significantly associated with age, presence of diabetes, CVD, serum phosphorus, eGFR, Urea and haemoglobin. Multi-adjusted stepwise regression analysis showed that lower eGFR levels (p<0.001), diabetes (p = 0.042), CVD (p = 0.009), smoking habit (p = 0.021) and higher serum phosphorus levels (p = 0.001) were associated with higher continuous RI. Serum phosphorus showed Area Under the Curves (AUC) values of 0.714 and 0.664 for discriminating RI cut-offs of 0.70 and 0.65.

CONCLUSIONS

This analysis suggests that RI is higher in CKD patients with CVD, diabetes, smoking habit and higher serum phosphorus, regardless of eGFR. Further studies are needed to verify whether higher RI indicates more complex pathway of intrarenal damage, besides and beyond kidney function.

Role of dietary phosphate restriction in chronic kidney disease

AIM

Patients with progressive chronic kidney disease (CKD) develop positive phosphate balance that is associated with increased cardiovascular risk and mortality. Modification of dietary phosphate is a commonly used strategy to improve outcomes but is complicated by the need for adequate dietary protein. Surprisingly, the evidence for patient-level benefits from phosphate restriction is tenuous, and the justification for using any phosphate binder for pre-dialysis patients is questionable.

METHODS

The evidence for dietary phosphate modification was reviewed, along with the possible role of a smart phone application (app) that provides information on phosphate, sodium, potassium and nutrients in over 50 000 Australian foods. A pilot study of healthy participants assigned to dietetic advice and standard diet sheets, or dietetic advice, diet sheets and use of the smart phone app was performed.

RESULTS

Following baseline studies, 25 participants commenced the sodium and phosphate restricted diet. After 2 weeks, both groups showed non-significant trends to reduction in urinary phosphate and sodium. App users referred to information on the app more frequently than the control group participants referred to written instructions, found referring to the app more convenient, felt they learned more new information, were more motivated to maintain the diet and were more likely to recommend their information source to family or friends (all P < 0.05).

CONCLUSIONS

Maintaining phosphate balance remains an important goal of CKD management, although diets incorporating very low phosphate and protein contents may worsen patient outcomes. For selected patients, a smart phone app may improve dietary acceptance and compliance.

Magnesium and Progression of Chronic Kidney Disease: Benefits Beyond Cardiovascular Protection?

Experimental and clinical studies have demonstrated that magnesium deficiency leads to hypertension, insulin resistance, and endothelial dysfunction, and is associated with an increased risk of cardiovascular events. Given that cardiovascular disease and CKD share similar risk factors, the low magnesium status may also contribute to CKD progression. In fact, lower serum magnesium levels and lower dietary magnesium intake are associated with an increased risk of incident CKD and progression to end-stage kidney disease. Because these associations are independent of traditional risk factors, other pathways might be involved in the relationship between magnesium deficiency and the risk of CKD progression. Recent evidence has shown that magnesium suppresses phosphate-induced vascular calcification. Magnesium impairs the crystallization of calcium phosphate-more specifically, the maturation of calciprotein particles. Considering that phosphate overload causes kidney damage, magnesium might counteract the phosphate toxicity to the kidney, as in the case of vascular calcification. This hypothesis is supported by an in vitro observation that magnesium alleviates proximal tubular cell injury induced by high phosphate. Potential usefulness of magnesium as a treatment option for phosphate toxicity in CKD should be further investigated by intervention studies.

Nicotinic acid and related compounds: A meta-analysis of their use for hyperphosphatemia in dialysis patients

BACKGROUND

Studies indicate that nicotinic acid and related compounds may decrease phosphorus concentrations effectively by reducing the absorption in the gastrointestinal tract. However, the efficacy and safety of oral niacin treatments have only been investigated in a limited number of small-scale studies.

METHODS

We performed this meta-analysis by pooling 12 qualified relevant preclinical and clinical trials to evaluate the association of nicotinic acid (and its related compounds) treatment and hyperphosphatemia among dialysis patients. Baseline and after treatment data were collected from the studies to evaluate drug efficacy, effect on lipid profile, and drug safety. To evaluate drug efficacy, subgroups were created based on different exposure time (i.e., 4 wks, 8 wks, 12 wks, and 24 wks) and each subgroup was compared against baseline data. In the assessment of lipid profile and drug safety, results of 8-week treatment were compared against baseline data.

RESULTS

Our study showed that in the efficacy assessment of drug treatment, serum phosphorus concentration was only significantly reduced in the 4-week (SMD, 0.68; 95% CI, 0.40 to 0.97; P = .000; n = 8), and 8-week (SMD, 1.05; 95% CI, 0.68 to 1.42; P = .000; n = 10) treatment groups. The calcium × phosphorus product showed significantly reduced concentration in all the drug exposure time settings, and no rebound was detected (4-wk treatment: SMD, 0.61; 95% CI, 0.18 to 1.04; P = .005; n = 5; 8-wk treatment: SMD, 0.76; 95% CI, 0.32 to 1.18, P = .001; n = 8; and 12-wks treatment: SMD, 0.28, 95% CI, -0.06 to 0.61; P = .103; n = 3). Lipid profile monitoring showed that high-density lipoprotein (HDL) and triglycerides (TG) significantly changed after 8 weeks of treatment (HDL: SMD, -0.63; 95% CI, -1.03 to 0.24; P = .002; n = 5) and TG: SMD, 0.25; 95% CI, 0.02 to 0.49; P = .033; n = 5). Assessment of drug safety detected significant association for incidence of diarrhea (8% incidence rate; 95% CI, 4% to 12%; P = .001) and total adverse event (41% incidence rate, 95% CI: 12% to 69%, P = .001).

CONCLUSION

Our study concludes that nicotinic acid and related compounds can significantly reduce serum phosphorus concentration with additive antilipemic effects. We also recommend that the safety of this drug be further studied, as our results suggest significant incidence of adverse events.

A novel fluorescent probe-based flow cytometric assay for mineral-containing nanoparticles in serum

Calciprotein particles, nanoscale aggregates of insoluble mineral and binding proteins, have emerged as potential mediators of phosphate toxicity in patients with Chronic Kidney Disease. Although existing immunochemical methods for their detection have provided compelling data, these approaches are indirect, lack specificity and are subject to a number of other technical and theoretical shortcomings. Here we have developed a rapid homogeneous fluorescent probe-based flow cytometric method for the detection and quantitation of individual mineral-containing nanoparticles in human and animal serum. This method allows the discrimination of membrane-bound from membrane-free particles and different mineral phases (amorphous vs. crystalline). Critically, the method has been optimised for use on a conventional instrument, without the need for manual hardware adjustments. Using this method, we demonstrate a consistency in findings across studies of Chronic Kidney Disease patients and commonly used uraemic animal models. These studies demonstrate that renal dysfunction is associated with the ripening of calciprotein particles to the crystalline state and reveal bone metabolism and dietary mineral as important modulators of circulating levels. Flow cytometric analysis of calciprotein particles may enhance our understanding of mineral handling in kidney disease and provide a novel indicator of therapeutic efficacy for interventions targeting Chronic Kidney Disease-Mineral Bone Disorder.

Association between plasma phosphorus and renal outcome: A prospective cohort of patients majorly with glomerulonephritis

AIM

Studies investigating the association between blood phosphorus and renal outcomes yielded inconsistent results, and studies from Asian population are extremely limited. We initiated the present cohort study, aiming to prospectively examine the association between blood phosphorus and adverse renal outcomes in a prospective chronic kidney disease (CKD) cohort of Chinese patients majorly with glomerulonephritis.

METHODS

A total of 1430 patients were involved in the study. Linear regression analyses were used to assess the relationship between phosphorus and the slope of estimated glomerular filtration rate (eGFR). Cox regression analyses were used to assess the association between phosphorus and composite outcomes, which were defined as the presence of at least one of: eGFR halving, end stage renal disease, or death.

RESULTS

During follow-up for an average of 41.4 months, 196 patients developed composite outcomes. The time-average plasma phosphorus was independently associated with the slope of eGFR (β = -0.18, 95% CI: -4.42 to -2.19, P < 0.001). Each 1 mg/dL increases of baseline and time-average phosphorus were respectively associated with a 1.33 (95% confidence interval (CI): 1.09-1.63; P = 0.005) and 2.79 (95%CI: 2.21-3.52; P < 0.001) fold higher risk of composite outcomes. Compared with participants in the bottom quartile of time-average phosphorus, those in the top quartile were at increased risk of composite outcomes, with a hazard ratio of 6.52 (95% CI: 3.05-13.90; P < 0.001).

CONCLUSION

Plasma phosphorus level is an independent risk factor of adverse renal outcomes in Chinese CKD patients majorly with glomerulonephritis. Compared with baseline value, time-average phosphorus has a stronger relationship with renal prognosis.

Epidemiology of low-proteinuric chronic kidney disease in renal clinics

CKD patients with low-grade proteinuria (LP) are common in nephrology clinics. However, prevalence, characteristics, and the competing risks of ESRD and death as the specific determinants, are still unknown. We analyzed epidemiological features of LP status in a prospective cohort of 2,340 patients with CKD stage III-V referred from ≥6 months in 40 nephrology clinics in Italy. LP status was defined as proteinuria <0.5 g/24h according to current KDIGO guidelines. Patients with higher proteinuria constituted the control group (CON). LP patients were 54.5% of the whole cohort. As compared to CON, LP were older (70.0±12.1 vs 65.4±14.1 y), and less likely to be male (55.8 vs 62.0%) and diabetic (27.6 vs 34.1%), and had hypertension as the most common cause of CKD (39.8%). They had higher eGFR (34.8±13.5 vs 26.8±13.2 mL/min/1.73m²) and hemoglobin (12.7±1.7 vs 12.3±1.7 g/dL), while systolic blood pressure (137±18 vs 140±18 mmHg) and serum phosphorus (3.7±0.8 vs 3.9±0.8 mg/dL) were lower [P<0.001 for all comparisons]. Over a median follow-up of 48 months, an inverse relative risk of ESRD and death was observed in LP (death>>ESRD; P = 0.002) versus CON (ESRD>>death; P<0.0001). Modifiable risk factors were also different in LP, with smoking, lower hemoglobin, and proteinuria being associated with higher mortality risk while lower BMI and higher phosphorus predicting ESRD at multivariable Cox analyses [P<0.05 for all]. Therefore, in nephrology clinics, LP patients are the majority and show distinctive basal features. More important, they are more exposed to death than ESRD and do present specific modifiable determinants of either outcome; indeed, in LP, while smoking plays a role for mortality, lower BMI and higher phosphorus levels -even if in the normal range- are predictors of ESRD. These data support the need to further study the low proteinuric CKD population to guide management.

Effects of Magnesium on the Phosphate Toxicity in Chronic Kidney Disease: Time for Intervention Studies

Magnesium, an essential mineral for human health, plays a pivotal role in the cardiovascular system. Epidemiological studies in the general population have found an association between lower dietary magnesium intake and an elevated risk of cardiovascular events. In addition, magnesium supplementation was shown to improve blood pressure control, insulin sensitivity, and endothelial function. The relationship between magnesium and cardiovascular prognosis among patients with chronic kidney disease (CKD) has been increasingly investigated as it is becoming evident that magnesium can inhibit vascular calcification, a prominent risk of cardiovascular events, which commonly occurs in CKD patients. Cohort studies in patients receiving dialysis have shown a lower serum magnesium level as a significant risk for cardiovascular mortality. Interestingly, the cardiovascular mortality risk associated with hyperphosphatemia is alleviated among those with high serum magnesium levels, consistent with in vitro evidence that magnesium inhibits high-phosphate induced calcification of vascular smooth muscle cells. Furthermore, a harmful effect of high phosphate on the progression of CKD is also attenuated among those with high serum magnesium levels. The potential usefulness of magnesium as a remedy for phosphate toxicity should be further explored by future intervention studies.

Ferritin Elevation and Improved Responsiveness to Erythropoiesis-Stimulating Agents in Patients on Ferric Citrate Hydrate

Introduction

In hemodialysis patients on ferric citrate hydrate, the increase in ferritin level is mainly due to the administration of the compound. We investigated possible other factors associated with ferritin level and how erythropoietin resistance index and erythropoiesis in those patients were affected. We looked at ferritin-elevating factors using data from a Japanese phase III long-term clinical trial of ferric citrate hydrate.

Methods

The factors with a strong association with ferritin levels at week 28 were selected by the process of variable selection. In addition, selected factors were analyzed by Mixed Model for Repeated Measurement. Subjects were divided into 3 groups by quantiles (<Q1, Q1-Q3, Q3<) of the most strongly correlated factors. Then the least-squares means of change of ferritin at each time point for each group were calculated. Finally, the differences of the least-squares means were examined. Changes of both erythropoiesis-stimulating agent dose and erythropoietin resistance index for each group were investigated. The differences in mean erythropoietin resistance index between groups at baseline, week 28, and week 52 were analyzed using t tests.

Results

Dose of ferric citrate hydrate showed the strongest correlation with change of ferritin and the second strongest was the reduction of erythropoiesis-stimulating agents. The mean erythropoietin resistance index was lowered in group <Q1. Group <Q1 showed significantly lower levels of ferritin at baseline.

Discussion

It is suggested that not only iron load but also the erythropoiesis-stimulating agent dose reduction may be involved in ferritin elevation during ferric citrate hydrate treatment, resulting in a decrease of erythropoietin resistance index.

PTH levels and not serum phosphorus levels are a predictor of the progression of kidney disease in elderly patients with advanced chronic kidney disease

BACKGROUND

At present, there is a high incidence of elderly patients with advanced chronic kidney disease (CKD) and it is important to know the long term progression and the factors that influence it.

OBJECTIVES

To analyse the progression of advanced CKD in elderly patients and the influence of bone-mineral metabolism.

METHODS

Retrospective study of 125 patients ≥70years of age with CKD stages 4-5 who started follow-up from January 1, 2007 to December 31, 2008, showing the progression of CKD (measured by the slope of the regression line of the estimated glomerular filtration rate [eGFR] by MDRD-4) over 5years.

RESULTS

Progression in the entire group (median and 25th and 75th percentiles): -1.15 (-2.8/0.17) ml/min/1.73m²/year, CKD-4: -1.3 (-2.8/0.03) ml/min/1.73m²/year, CKD-5: -1.03 (-3.0/0.8) ml/min/1.73m²/year; the slope of the regression line was positive in 35 patients (28%: CKD does not progress) and negative in 90 patients (72%: CKD progresses). Negative correlation (Spearman) (slower progression): PTH, albumin/Cr ratio and daily Na excretion (all baseline measurements). No correlation with eGFR, serum P, urinary P excretion, protein intake and intake of P (all baseline measurements). In the linear regression analysis (dependent variable: slope of progression): albuminuria and PTH (both at baseline measurements) influenced this variable independently. Logistic regression (progresses vs. does not progress): PTH, albuminuria and eGFR (all at baseline measurements) influenced significantly.

CONCLUSIONS

In our group of elderly patients, impairment of renal function is slow, particularly in CKD-5 patients. Albuminuria and PTH at baseline levels are prognostic factors in the evolution of renal function.

Fibroblast Growth Factor 23 and Risk of CKD Progression in Children

BACKGROUND AND OBJECTIVES

Plasma fibroblast growth factor 23 (FGF23) concentrations increase early in the course of CKD in children. High FGF23 levels associate with progression of CKD in adults. Whether FGF23 predicts CKD progression in children is unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We tested the hypothesis that high plasma FGF23 is an independent risk factor for CKD progression in 419 children, aged 1-16 years, enrolled in the Chronic Kidney Disease in Children (CKiD) cohort study. We measured plasma FGF23 concentrations at baseline and determined GFR annually using plasma disappearance of iohexol or the CKiD study estimating equation. We analyzed the association of baseline FGF23 with risk of progression to the composite end point, defined as start of dialysis or kidney transplantation or 50% decline from baseline GFR, adjusted for demographics, baseline GFR, proteinuria, other CKD-specific factors, and other mineral metabolites.

RESULTS

At enrollment, median age was 11 years [interquartile range (IQR), 8-15], GFR was 44 ml/min per 1.73 m2 (IQR, 33-57), and FGF23 was 132 RU/ml (IQR, 88-200). During a median follow-up of 5.5 years (IQR, 3.5-6.6), 32.5% of children reached the progression end point. Higher FGF23 concentrations were independently associated with higher risk of the composite outcome (fully adjusted hazard ratio, 2.52 in the highest versus lowest FGF23 tertile; 95% confidence interval, 1.44 to 4.39, P=0.002; fully adjusted hazard ratio, 1.33 per doubling of FGF23; 95% confidence interval, 1.13 to 1.56, P=0.001). The time to progression was 40% shorter for participants in the highest compared with the lowest FGF23 tertile. In contrast, serum phosphorus, vitamin D metabolites, and parathyroid hormone did not consistently associate with progression in adjusted analyses.

CONCLUSIONS

High plasma FGF23 is an independent risk factor for CKD progression in children.

Cost-effectiveness of phosphate binders among patients with chronic kidney disease not yet on dialysis: a long way to go

Hyperphosphatemia management is integral to the management of patients with chronic kidney disease. This mineral abnormality is associated with greater costs, but so is its management, especially with the use novel phosphate binders. The economic evaluation of these pharmaceutical agents is increasingly needed to provide evidence for value of money spent and inform resource allocation. Recently, Nguyen et al. explored the economical attractiveness of Sevelamer relative to Calcium Carbonate among patients with chronic kidney disease not yet on dialysis and concluded that the former was cost-effective. The current commentary discusses the results of this analysis and sheds light on the methodological challenges of economic evaluations in this field.

The Impact of Normal Range of Serum Phosphorus on the Incidence of End-Stage Renal Disease by A Propensity Score Analysis

Background

Although hyperphosphatemia is deemed a risk factor of the progression of chronic kidney disease (CKD), it remains unclear whether the normal range of serum phosphorus likewise deteriorates CKD. A propensity score analysis was applied to examine the causal effect of the normal range of serum phosphorus on the incidence of end-stage renal disease (ESRD).

Methods

A retrospective CKD cohort of 803 participants in a single institution was analyzed. Propensity score was estimated using 22 baseline covariates by multivariate binary logistic regression for the different thresholds of time-averaged phosphorus (TA-P) in the normal range of serum phosphorus incremented by 0.1 mg/dL from 3.3 to 4.5 mg/dL.

Results

The incidence rate of ESRD was 33.9 per 1,000 person-years over median follow-up of 4.3 years. Total patients showed the mean baseline phosphorus of 3.37 mg/dL and were divided to quartile. The higher quartile was associated with the parameters consistent with the advancement of CKD. A stratified Cox regression showed the highest hazard ratio (HR) at TA-P 3.4 mg/dL (HR 17.60, 95% CI 3.92–78.98) adjusted for baseline covariates such as sex, age, diabetic nephropathy, estimated GFR, serum albumin, Na-Cl, phosphorus, LDL-C and proteinuria. Adjusted HRs remained high up to TA-P 4.2 mg/dL (HR 2.22, 95% CI 1.33–3.71). After propensity score matching conducted at the thresholds of TA-P 3.4, 3.6, 3.8 and 4.0 mg/dL, the higher levels of TA-P showed the higher HRs by Kaplan-Meier analysis (p < 0.05 by stratified log-rank test). The numbers needed to treat were calculated as 3.9 to 5.3 over 5 years.

Conclusions

The propensity score analysis shows that even the normal range of serum phosphorus clearly accelerates CKD progression to ESRD. Our results encourage clinicians to target serum phosphorus to inhibit CKD progression in the manner of ‘the lower the better.’

Con: Phosphate binders in chronic kidney disease

Phosphate binders are prescribed to chronic kidney disease (CKD) patients based on associations of serum phosphate concentrations with mortality and calcification, experimental evidence for direct calcifying effects of phosphate on vascular smooth muscle tissue and the central importance of phosphate retention in CKD-mineral and bone disorder (CKD-MBD). Current knowledge regarding phosphate metabolism in CKD provides important insight into disease mechanisms and supports future clinical trials of phosphate binders in CKD patients to determine the impact of these medications on clinically relevant outcomes. The risks and benefits of phosphate binders cannot be inferred from association studies of serum phosphate concentrations, which are inconsistent and subject to confounding, animal-experimental data, which are based on conditions that differ from human disease, or physiological arguments, which are limited to known regulatory factors. Many interventions that targeted biochemical pathways suggested by association studies and suspected biological importance have yielded null or harmful results. Clinical trials of phosphate binders are of high clinical and scientific importance to nephrology. Demonstration of reduced rates of clinical disease in such trials could lead to important health benefits for CKD patients, whereas negative results would refocus efforts to understand and treat CKD-MBD. Clinical trials that employ highly practical or 'pragmatic' designs represent an optimal approach for determining the safety and effectiveness of phosphate binders in real-world settings. Absent clinical trial data, observational studies of phosphate binders in large CKD populations could provide important information regarding the benefits, risks and/or unintended side effects of these medications.

Sex, Age, and the Association of Serum Phosphorus With All-Cause Mortality in Adults With Normal Kidney Function

BACKGROUND

High serum phosphorus levels are associated with cardiovascular morbidity and mortality in kidney disease. Although serum phosphorus levels possibly influence on mortality in individuals without kidney disease, this is uncertain because of the variable sex- and age-based distribution of serum phosphorus levels.

STUDY DESIGN

Observational cohort study.

SETTING & PARTICIPANTS

Clinical and biochemical data were collected from 138,735 adults undergoing routine health checkups in 3 tertiary hospitals. Individuals with estimated glomerular filtration rates < 60 mL/min/1.73 m2 and urine dipstick albumin ≥ 1+ were excluded.

PREDICTOR

Sex-specific quartiles of serum phosphorus and sex.

OUTCOMES

All-cause mortality.

RESULTS

The study included 92,756 individuals. Generally, women showed higher serum phosphorus levels than men. In women, serum phosphorus levels increased with age until 60 years old, then decreased with age. Men with higher serum phosphorus levels were younger and less likely to have hypertension, whereas women with higher serum phosphorus levels were older and more likely to have diabetes and hypertension. During a median follow-up of 75 months, 1,646 participants died. In the overall population, higher serum phosphorus levels were an independent predictor for all-cause mortality after adjustment (adjusted HR for the highest vs. lowest quartile, 1.34; 95% CI, 1.15-1.56; P<0.001). We observed that this increased risk was present in men but not in women (adjusted HR of 1.43 [95% CI, 1.22-1.68] vs. 1.01 [95% CI, 0.76-1.33]), but interaction by sex was not significant (P=0.8).

LIMITATIONS

A single phosphorus measurement and low power to test for interactions by sex and age.

CONCLUSIONS

We demonstrated that higher serum phosphorus levels influenced all-cause mortality in individuals with normal kidney function. Our findings suggest that the association may differ by sex, but future studies with adequate power to test for effect modification are needed to confirm our findings.

Novel iron-containing phosphate binders for treatment of hyperphosphatemia

INTRODUCTION

Hyperphosphatemia is a frequent complication of chronic kidney disease and is associated with increased mortality. Despite side effects, risk of accumulation and high costs, phosphate binders (PBs) have become the crucial cornerstone of therapy. The iron-containing PB sucroferric oxyhydroxide (SO) and ferric citrate hydrate (FCH) have entered the market and other candidates are prior market entry.

AREAS COVERED

A literature search was performed using MEDLINE and EMBASE databases to identify references on iron-containing PB with particular regard to efficacy, safety and potential benefits. Additional hand searches were conducted along with a full-text review of any citation that appeared relevant.

EXPERT OPINION

On the highly competitive market, where the 'ideal' PB is still unknown, novel substances that offer clear benefits over available drugs are desired. Although SO and FCH showed similar efficacy and safety compared to sevelamer, head-to-head studies with lanthanum carbonate are absent. Clinical 1-year data in a limited patient cohort suggested improved adherence for SO and a large randomized controlled trial showed significant reduction in hospitalizations and costs for FCH. Additional large randomized controlled trials have now to prove these possible advantages. Cost-effectiveness in comparison to other PB and the exclusion of significant harms under long-term treatment will determine the future use of both drugs.

Dysmagnesemia in Hospitalized Patients: Prevalence and Prognostic Importance

OBJECTIVE

To examine the prevalence of serum magnesium (Mg) alterations and outcomes in hospitalized patients.

PATIENTS AND METHODS

All admissions to Mayo Clinic in Rochester, Minnesota, from January 1, 2009, through December 31, 2013 (288,120 patients), were screened. Admission Mg from each unique patient and relevant clinical data were extracted from the institutional electronic database.

RESULTS

After excluding patients aged less than 18 years, those without Mg measurement, and readmission episodes, a total of 65,974 patients were studied. Magnesium levels of 2.1 mg/dL or higher were found in 20,777 patients (31.5%), and levels less than 1.7 mg/dL were noted in 13,320 (20.2%). Hypomagnesemia was common in patients with hematologic/oncological disorders, and hypermagnesemia was common in those with cardiovascular disease. The lowest hospital mortality, assessed by restricted cubic spline and percentage death, occurred in patients with Mg levels between 1.7 and 1.89 mg/dL. An Mg level of less than 1.7 mg/dL was independently associated with an increased risk of hospital mortality after adjusting for all variables except the admission diagnosis; risk for longer hospital stay and being discharged to a care facility were increased in the fully adjusted model. An elevated Mg level of 2.3 mg/dL or higher was a predictor for all adverse outcomes. The magnitude of Mg elevations in patients with levels of 2.3 mg/dL or higher (N=7908) was associated with worse hospital mortality in a dose-response manner. In patients with cardiovascular diseases, Mg levels of 1.5 to 1.69 mg/dL and 2.3 mg/dL or higher both independently predicted poor outcomes including hospital mortality.

CONCLUSION

Dysmagnesemia in hospitalized patients is common, with hypermagnesemia being most prevalent. Compared with hypomagnesemia, hypermagnesemia is a stronger predictor for poor outcomes. Magnesium supplementation for patients without Mg deficiency should be avoided in the absence of randomized controlled trials documenting a benefit.

Magnesium modifies the association between serum phosphate and the risk of progression to end-stage kidney disease in patients with non-diabetic chronic kidney disease

It is known that magnesium antagonizes phosphate-induced apoptosis of vascular smooth muscle cells and prevents vascular calcification. Here we tested whether magnesium can also counteract other pathological conditions where phosphate toxicity is involved, such as progression of chronic kidney disease (CKD). We explored how the link between the risk of CKD progression and hyperphosphatemia is modified by magnesium status. A post hoc analysis was run in 311 non-diabetic CKD patients who were divided into four groups according to the median values of serum magnesium and phosphate. During a median follow-up of 44 months, 135 patients developed end-stage kidney disease (ESKD). After adjustment for relevant clinical factors, patients in the lower magnesium-higher phosphate group were at a 2.07-fold (95% CI: 1.23-3.48) risk for incident ESKD and had a significantly faster decline in estimated glomerular filtration rate compared with those in the higher magnesium-higher phosphate group. There were no significant differences in the risk of these renal outcomes among the higher magnesium-higher phosphate group and both lower phosphate groups. Incubation of tubular epithelial cells in high phosphate and low magnesium medium in vitro increased apoptosis and the expression levels of profibrotic and proinflammatory cytokine; these changes were significantly suppressed by increasing magnesium concentration. Thus, magnesium may act protectively against phosphate-induced kidney injury.

SELF-REPORTED MEDICATION ADHERENCE IN PATIENTS WITH END-STAGE KIDNEY DISEASE UNDERGOING ONLINE-HAEMODIAFILTRATION

INTRODUCTION

Non-adherence to therapeutic regimens is a recognised problem in the dialysis population that compromises the opportunity to achieve maximum treatment effect and, therefore, might lead to increased morbidity and mortality. In this study, we aimed to evaluate the prevalence of self-reported medication non-adherence in patients with end-stage kidney disease (ESKD) undergoing online-haemodiafiltration (OL-HDF), as well as to evaluate the factors that could affect medication adherence.

PATIENTS AND METHODS

We evaluated 122 patients with ESKD undergoing OL-HDF. Patients' reported medication adherence was measured by the Measure Treatment Adherence (MTS) scale. Social support was evaluated by the abbreviated Lubben Social Network Scale (LSNS); depression status by the Geriatric Depression Scale (GDS). Socio-demographic, co-morbidity and clinical data were also evaluated.

RESULTS

Our results showed that 10.7% of patients with ESKD perceived themselves as non-adherent to medication. When two groups of patients (adherent and non-adherents) were compared, significantly higher levels of triglycerides, and higher diastolic and systolic blood pressure were found in the non-adherent group. Significant correlations were found between the MTS score, and diastolic blood pressure, age and GDS score. Multiple regression analysis identified age and the GDS score as independent variables significantly associated with the MTS score.

CONCLUSIONS

Non-adherence to therapeutic regimens in patients with ESKD is associated with higher levels of triglycerides and higher blood pressure and are, therefore, at a higher cardiovascular risk. Moreover, we found that age and depression status are important variables in non-adherence to therapeutic regimens.

Serum Phosphorus and Progression of CKD and Mortality: A Meta-analysis of Cohort Studies

BACKGROUND

Recent studies have indicated that phosphorus may play an independent pathogenic role in chronic kidney disease (CKD) progression, but some of those studies were underpowered and yielded inconsistent results.

STUDY DESIGN

Systematic review and meta-analysis.

SETTING & POPULATION

Non-dialysis-dependent patients with CKD (transplant recipients were excluded).

SELECTION CRITERIA FOR STUDIES

Studies assessing the risk ratio of serum phosphorus level on kidney failure and mortality for non-dialysis-dependent patients with CKD published from January 1950 to June 2014 were included following systematic searching of MEDLINE, EMBASE, and the Cochrane Library.

PREDICTOR

Serum phosphorus level.

OUTCOME

Kidney failure, defined as doubled serum creatinine level, 50% decline in estimated glomerular filtration rate, or end-stage kidney disease.

RESULTS

In 12 cohort studies with 25,546 patients, 1,442 (8.8%) developed kidney failure and 3,089 (13.6%) died. Overall, every 1-mg/dL increase in serum phosphorus level was associated independently with increased risk of kidney failure (hazard ratio, 1.36; 95% CI, 1.20-1.55) and mortality (hazard ratio, 1.20; 95% CI, 1.05-1.37).

LIMITATIONS

Existence of potential residual confounding could not be excluded.

CONCLUSIONS

This meta-analysis suggests an independent association between serum phosphorus level and kidney failure and mortality among non-dialysis-dependent patients with CKD and suggests that large-scale randomized controlled trials should target disordered phosphorus homeostasis in CKD.

Predictors of health-related quality of life perceived by end-stage renal disease patients under online hemodiafiltration

PURPOSE

Patients' perception of health-related quality of life (HRQOL) is a consistent and powerful predictor of the outcome of end-stage renal disease (ESRD) patients under dialysis. This study aims to identify factors that could affect the HRQOL of ESRD patients under online hemodiafiltration (OL-HDF).

METHODS

We evaluated 322 ESRD patients under OL-HDF (59.63% males; 64.9 ± 14.3 years old) from five dialysis units in the north of Portugal. Socio-demographic data, comorbidities, hematological data, iron status, dialysis adequacy, nutritional and inflammatory markers were collected from patients records. Patient's reported HRQOL score was assessed by using the Kidney Disease Quality of Life-Short Form (KDQOL-SF).

RESULTS

ESRD patients showed a mean (± SD) of 53.17% (± 15.31%) in SF-36 total score, 50.17% (± 9.51%) in the SF-36 mental component summary (MCS) and 49.75% (± 9.44%) in the SF-36 physical component summary (PCS). Red cell distribution width (RDW), feminine gender and diabetes were found as significant predictors of SF-36 total score of HRQOL, which accounts for 12% of the total explained variance. Patient satisfaction, RDW, body mass index and gender were identified as predictors for the PCS, which accounts for 22% of total explained variance. Furthermore, patient satisfaction and dry weight were found as predictors for MCS. These predictors accounted for 28% of the total explained variance.

CONCLUSIONS

Our results showed that the coexistence of diabetes, gender and erythropoietic disturbances are predictors of HRQOL in patients under OL-HDF and suggest that more attention should be given to woman patients, to the improvement of anemia and to diabetic patients, who are more prone to perceive a worst HRQOL.

A 12-week, double-blind, placebo-controlled trial of ferric citrate for the treatment of iron deficiency anemia and reduction of serum phosphate in patients with CKD Stages 3-5

BACKGROUND

Iron deficiency anemia and serum phosphate levels > 4.0mg/dL are relatively common in chronic kidney disease stages 3 to 5 and are associated with higher risks of progressive loss of kidney function, cardiovascular events, and mortality.

STUDY DESIGN

Double-blind, placebo-controlled, randomized trial.

SETTING & PARTICIPANTS

149 patients with estimated glomerular filtration rates < 60 mL/min/1.73 m(2), iron deficiency anemia (hemoglobin, 9.0-12.0 g/dL; transferrin saturation [TSAT]≤ 30%, serum ferritin ≤ 300 ng/mL), and serum phosphate levels ≥ 4.0 to 6.0mg/dL. Use of intravenous iron or erythropoiesis-stimulating agents was prohibited.

INTERVENTION

Randomization to treatment for 12 weeks with ferric citrate coordination complex (ferric citrate) or placebo.

OUTCOMES & MEASUREMENTS

Coprimary end points were change in TSAT and serum phosphate level from baseline to end of study. Secondary outcomes included change from baseline to end of treatment in values for ferritin, hemoglobin, intact fibroblast growth factor 23 (FGF-23), urinary phosphate excretion, and estimated glomerular filtration rate.

RESULTS

Ferric citrate treatment increased mean TSAT from 22% ± 7% (SD) to 32% ± 14% and reduced serum phosphate levels from 4.5 ± 0.6 to 3.9 ± 0.6 mg/dL, while placebo exerted no effect on TSAT (21% ± 8% to 20% ± 8%) and less effect on serum phosphate level (4.7 ± 0.6 to 4.4 ± 0.8 mg/dL; between-group P<0.001 for each). Ferric citrate increased hemoglobin levels (from 10.5 ± 0.8 to 11.0 ± 1.0 g/dL; P<0.001 vs placebo), reduced urinary phosphate excretion 39% (P<0.001 vs placebo), and reduced serum intact FGF-23 levels from a median of 159 (IQR, 102-289) to 105 (IQR, 65-187) pg/mL (P=0.02 vs placebo). The incidence and severity of adverse effects were similar between treatment arms.

LIMITATIONS

The study is limited by relatively small sample size and short duration and by having biochemical rather than clinical outcomes.

CONCLUSIONS

Short-term use of ferric citrate repletes iron stores, increases hemoglobin levels, and reduces levels of serum phosphate, urinary phosphate excretion, and FGF-23 in patients with chronic kidney disease stages 3 to 5.

Nutrition for the prevention and treatment of chronic kidney disease in diabetes

The prevention and treatment of chronic kidney disease (CKD) in diabetes through diet and lifestyle have been a topic of much interest over the years. Consideration of the type and amount of carbohydrate, protein and fat is required for optimal blood glucose control, for clinical outcomes related to renal function and for consideration of risk reduction for cardiovascular disease. Controversy has existed regarding the clinical significance of a protein-controlled diet, not to mention the ideal recommended intake in view of the benefits and risks. Furthermore, the level of CKD with which to implement dietary changes should also be considered. This review seeks to provide guidance and clarity concerning the nutritional management of CKD in diabetes.

The use of fibroblast growth factor 23 testing in patients with kidney disease

The emergence of fibroblast growth factor 23 as a potentially modifiable risk factor in CKD has led to growing interest in its measurement as a tool to assess patient risk and target therapy. This review discusses the analytical and clinical challenges faced in translating fibroblast growth factor 23 testing into routine practice. As for other bone mineral markers, agreement between commercial fibroblast growth factor 23 assays is poor, mainly because of differences in calibration, but also, these differences reflect the variable detection of hormone fragments. Direct comparison of readout from different assays is consequently limited and likely hampers setting uniform fibroblast growth factor 23-directed targets. Efforts are needed to standardize assay output to enhance clinical use. Fibroblast growth factor 23 is robustly associated with cardiovascular and renal outcomes in patients with CKD and adds value to risk assessments based on conventional risk factors. Compared with most other mineral markers, fibroblast growth factor 23 shows better intraindividual temporal stability, with minimal diurnal and week-to-week variability, but substantial interindividual variation, maximizing discriminative power for risk stratification. Conventional therapeutic interventions for the CKD-mineral bone disorder, such as dietary phosphate restriction and use of oral phosphate binders or calcimimetics, are associated with variable efficacy at modulating circulating fibroblast growth factor 23 concentrations, like they are for other mineral metabolites. Dual therapy with dietary phosphate restriction and noncalcium-based binder use achieves the most consistent fibroblast growth factor 23-lowering effect and seems best monitored using an intact assay. Additional studies are needed to evaluate whether strategies aimed at reducing levels or antagonizing its action have beneficial effects on clinical outcomes in CKD patients. Moreover, a better understanding of the mechanisms driving fibroblast growth factor 23 elevations in CKD is needed to inform the use of therapeutic interventions targeting fibroblast growth factor 23 excess. This evidence must be forthcoming to support the use of fibroblast growth factor 23 measurement and fibroblast growth factor 23-directed therapy in the clinic.

A randomized multicenter trial of paricalcitol versus calcitriol for secondary hyperparathyroidism in stages 3-4 CKD

BACKGROUND AND OBJECTIVES

Calcitriol is used to treat secondary hyperparathyroidism in patients with CKD. Paricalcitol is less calcemic and phosphatemic in preclinical studies and in some trials in dialysis patients, but head-to-head comparisons in nondialysis patients are lacking. A large meta-analysis of trials concluded that these agents did not consistently reduce parathyroid hormone (PTH) and increased the risk of hypercalcemia and hyperphosphatemia. Therefore, the objective of this multicenter trial was to compare the rate of hypercalcemia between calcitriol and paricalcitol, while suppressing PTH 40%-60%.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Patients with stages 3-4 CKD (n=110) with a PTH level >120 pg/ml were recruited and randomized to 0.25 μg/d of calcitriol or 1 μg/d of paricalcitol between April 2009 and July 2011. Subsequent dose adjustments were by protocol to achieve 40%-60% PTH suppression below baseline. The primary endpoint was the rate of confirmed hypercalcemia of >10.5 mg/dl between groups.

RESULTS

Forty-five patients in each group completed the 24 weeks of treatment. Both agents suppressed PTH effectively (-52% with paricalcitol and -46% with calcitriol; P=0.17), although the paricalcitol group reached a 40% reduction in PTH sooner at a median 8 weeks (interquartile range [IQR], 4, 12) versus 12 weeks (IQR, 8, 18; P=0.02) and had a lower pill burden of 240 (IQR, 180, 298) versus 292 (IQR, 231, 405; P=0.01). Confirmed hypercalcemia was very low in both groups (three with paricalcitol and one with calcitriol) and was not significantly different (P=0.36). Both groups had small increases in calcium and phosphorus levels (0.3-0.4 mg/dl in each electrolyte) and significant decreases in alkaline phosphatase, a marker of high bone turnover, with no significant differences between groups.

CONCLUSIONS

These results show that both calcitriol and paricalcitol achieved sustained PTH and alkaline phosphatase suppression in stages 3-4 CKD, with small effects on serum calcium and phosphorus and a low incidence of hypercalcemia.

Serum phosphorus in people with chronic kidney disease: you are what you eat

This issue of Kidney International includes two important articles about serum phosphorus and its treatment. The article by Cannata-Andía and colleagues describes a rigorous observational study of the association between serum phosphorus level, phosphate binder use, and clinical outcomes including all-cause and cardiovascular mortality. The article by Mehrotra and colleagues addresses the association between serum phosphorus, socioeconomic status, and mortality among participants in the US-based KEEP program.

Serum phosphorus and mortality in the Third National Health and Nutrition Examination Survey (NHANES III): effect modification by fasting

BACKGROUND

Serum phosphorus levels have been associated with mortality in some but not all studies. Because dietary intake prior to measurement can affect serum phosphorus levels, we hypothesized that the association between serum phosphorus level and mortality is strongest in those who have fasted longer.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

Nationally representative sample of 12,984 participants 20 years or older in the Third National Health and Nutrition Examination Survey (1988-1994).

FACTORS

Serum phosphorus level, fasting duration (dichotomized as ≥ 12 or < 12 hours).

OUTCOMES

All-cause and cardiovascular mortality determined by death certificate data from the National Death Index.

MEASUREMENTS

Serum phosphorus measured in a central laboratory and fasting duration recorded as time since food or drink other than water was consumed.

RESULTS

Individuals fasting 12 or more hours had lower serum phosphorus levels than those fasting less than 12 hours (3.34 vs 3.55 mg/dL; P < 0.001) and higher correlation with repeat measurement (0.66 vs 0.53; P = 0.002). In multivariable-adjusted Cox regression models, the highest quartile of serum phosphorus was associated with increased mortality in participants fasting 12 or more hours (adjusted HR, 1.74; 95% CI, 1.38-2.20; reference, lowest quartile) but not in participants fasting less than 12 hours (adjusted HR, 1.08; 95% CI, 0.89-1.32; P for interaction = 0.002). Relationships were consistent using 8 hours as the fasting cutoff point or cardiovascular mortality as the outcome.

LIMITATIONS

Observational study, lack of fibroblast growth factor 23 or intact parathyroid hormone measurements.

CONCLUSIONS

Fasting but not nonfasting serum phosphorus levels were associated with increased mortality. Risk prognostication based on serum phosphorus may be improved using fasting levels.

Phosphorus and the kidney: What is known and what is needed

A major role of the kidneys is to maintain phosphorus homeostasis. High serum phosphorus has been linked to all-cause and cardiovascular mortality in chronic kidney disease (CKD) both before and after initiation of renal replacement therapy. Considering the clinical implications of uncontrolled hyperphosphatemia, maintenance of phosphorus concentrations within an optimum range is standard of care in this patient population. Recently, the epidemiologic associations between serum phosphorus and worse outcome have been extended to the general population. This becomes even more important in view of the increasing dietary phosphorus intake in the American diet due in large part to the greater consumption of foods processed with phosphate additives. A greater understanding of mechanisms and epidemiology of altered phosphorus metabolism and disease in CKD may help clarify the possible role of excess dietary phosphorus as a health risk factor in the general population.

A within-patient analysis for time-varying risk factors of CKD progression

Recent data suggest that nonlinear GFR trajectories are common among patients with CKD, but the modifiable risk factors underlying these changes in CKD progression rate are unknown. Analyses relating baseline risk factors to subsequent GFR decline are suboptimal because these relationships often attenuate as follow-up time increases and these analyses do not account for temporal changes in risk factors. We identified 74 participants in the African American Study of Kidney Disease and Hypertension who had both a period of rapid GFR decline and an extended period of stability during a follow-up period of ≥12 years. We performed a within-patient comparison of time-varying risk factors measured during the periods of GFR decline and stability and identified several risk factors associated with faster GFR decline: more hospitalization episodes and hospitalization days per year; higher BP, serum phosphorus, and urine protein-to-creatinine ratio; lower serum albumin and urine sodium-to-potassium ratio; slower rate of decline of serum urea nitrogen, serum creatinine, serum uric acid, and serum phosphorus; and faster rate of decline of serum hematocrit and serum bicarbonate. By allowing each patient to serve as his or her own control, this novel, within-patient analytic approach holds considerable promise as a means to identify time-varying risk factors associated with stabilization of GFR or acceleration of GFR decline.

Dietary phosphorus and kidney disease

High serum phosphate is linked to poor health outcome and mortality in chronic kidney disease (CKD) patients before or after the initiation of dialysis. Therefore, maintenance of normal serum phosphate levels is a major concern in the clinical care of this population with dietary phosphorus restriction and/or use of oral phosphate binders considered to be the best corrective care. This review discusses (1) evidence for an association between serum phosphate levels and bone and cardiovascular disease (CVD) in CKD patients as well as progression of kidney disease itself; (2) the relationship between serum phosphate and dietary phosphorus intake; and (3) implications from these data for future research. Increasing our understanding of the relationship between altered phosphorus metabolism and disease in CKD patients may clarify the potential role of excess dietary phosphorus as a risk factor for disease in the general population.