Hyperphosphataemia and related mortality

Frequent hemodialysis: history of the modality and assessment of outcomes

About 660,000 individuals have end-stage renal disease in the USA, the vast majority of whom are receiving standard, in-center, thrice-weekly hemodialysis (HD). The morbidity and mortality among patients receiving standard HD remain unacceptably high. Studies conducted over the past two decades have provided a substantial amount of information on the advantages and drawbacks of providing more frequent HD treatment, either in-center or at home. In this article I summarize these studies, focusing special attention on the randomized, cross-over study assessing outcomes in children who received either frequent, in-center HD or traditional, thrice-weekly, in-center HD performed by Laskin et al. (Pediatr Nephrol doi: 10.1007/s00467-017-3656-x , 2017).

Hypophosphatemia: nutritional status, body composition, and mortality in hemodialysis patients

PURPOSE

The aim of the present study was to investigate the relationship between serum phosphate levels, clinical parameters, body composition, and mortality.

METHODS

Multicenter longitudinal observational study of a cohort of 3552 patients in hemodialysis (HD) from 34 Nephrocare dialysis units in Portugal with 24 months of follow-up. Patients were divided into three groups depending on their serum phosphorus (<3.5; 3.5-5.5; >5.5 mg/dL). Statistical tests were performed with SPSS, version 20.0. A p < 0.05 was considered significant.

RESULTS

On the one hand, hypophosphatemia was significantly associated with better dialysis adequacy, higher age and overhydration. On the other hand, it was associated with lower albumin, protein intake, creatinine, hemoglobin, calcium, potassium, magnesium, body mass index (BMI), body cell mass index, fat tissue index and lean tissue index. These patients had lower survival rates compared with those with normo- and hyperphosphatemia. Hypophosphatemia was a predictor of death when adjusted for age, diabetes, HD vintage, gender, and Kt/V. Comparing the mortality predictors in hypo- and hyperphosphatemia, we found that low albumin, BMI, and high overhydration increased the mortality risk in the hypophosphatemic group, whereas in hyperphosphatemic patients data were not statistically significant.

CONCLUSION

Currently, a high prevalence of hypophosphatemia exists in Portuguese HD patients. This condition is associated with worst nutritional and body composition parameters. In the context of additional indices of malnutrition (low albumin, low BMI or severe overhydration), hypophosphatemic patients presented higher mortality risk.

Phosphorus metabolism in peritoneal dialysis- and haemodialysis-treated patients

BACKGROUND

Phosphorus control is generally considered to be better in peritoneal dialysis (PD) patients as compared with haemodialysis (HD) patients. Predialysis phosphorus concentrations are misleading as a measure of phosphorus exposure in HD, as these neglect significant dialysis-related fluctuations.

METHODS

Parameters of mineral metabolism, including parathyroid hormone (PTH) and fibroblast growth factor-23 (FGF-23), were determined in 79 HD and 61 PD patients. In PD, phosphorus levels were determined mid-morning. In HD, time-averaged phosphorus concentrations were modelled from measurements before and after the mid-week dialysis session. Weekly renal, dialytic and total phosphorus clearances as well as total mass removal were calculated from urine and dialysate collections.

RESULTS

Time-averaged serum phosphorus concentrations in HD (3.5 ± 1.0 mg/dL) were significantly lower than the mid-morning concentrations in PD (5.0 ± 1.4 mg/dL, P < 0.0001). In contrast, predialysis phosphorus concentrations (4.6 ± 1.4 mg/dL) were not different from PD. PTH and FGF-23 levels were significantly higher in PD. Despite higher residual renal function, total phosphorus clearance was significantly lower in PD (P < 0.0001). Total phosphorus mass removal, conversely, was significantly higher in PD (P < 0.05).

CONCLUSIONS

Our data suggest that the time-averaged phosphorus concentrations in patients treated with PD are higher as compared with patients treated with HD. Despite a better preserved renal function, total phosphorus clearance is lower in patients treated with PD. Additional studies are needed to confirm these findings in a population with a different demographic profile and dietary background and to define clinical implications.

[Indications for parathyroidectomy in renal hyperparathyroidism: comments on the significance of new therapeutics]

New therapeutics for the treatment of chronic kidney disease and secondary hyperparathyroidism, such as calcium and aluminium-free phosphate binders, calcimimetic agents and active vitamin D metabolites may decrease the need for parathyroidectomy. The calcimimetic cinacalcet does not induce a longer lasting regression of renal hyperparathyroidism and autonomous growing of parathyroids and the therapeutic effect is limited to the period of treatment. The classical indications for surgery, hypercalcemia, vascular calcification, severe osteopathy, drug-resistant hyperphosphatemia and calciphylaxis are still valid if patients do not respond to medical therapy under the condition that adynamic bone disease is excluded. Individual operative risk factors and improvement of quality of life are important supplementary factors for the indication for parathyroidectomy.

Did 20 years of technological innovations in hemodialysis contribute to better patient outcomes?

During the past two decades, impressive technological innovations have been introduced in the field of hemodialysis. This review analyzes whether these have been translated into better patient survival. The potential impacts of an increase in dialysis dosage, the preference of high-flux versus low-flux membranes, the choice between convection and diffusion as dialysis strategy, the chemical composition and biologic purity of dialysate, the effect of sodium, potassium, volume profiling, and the intradialytic volume monitoring aiming at improving hemodynamic stability are explored. Studies in which the dialysis dosage was increased were not associated with increased patient survival, whereas the superiority of high-flux over low-flux membranes is not convincingly demonstrated. Although strict evidence is lacking, observational data suggest an advantage of convective over pure diffusive strategies. Longer duration of the dialysis sessions and/or higher frequency of dialysis is probably beneficial, but the results of powerful randomized, controlled trials should be awaited. Sodium profiling has more disadvantages than advantages, whereas potassium profiling mainly in arrhythmia-prone patients with ventricular hypertrophy should be considered. Intradialytic blood volume monitoring has reduced intradialytic hypotension episodes, but hard evidence for improving patient survival is lacking. Overall, the major technological advances in dialysis have not yet been translated into longer patient survival. Optimal predialysis care in preventing the cardiovascular damage that accumulates before the start of dialysis and timely creation of an arteriovenous fistula as vascular access is a more effective and more economic strategy in the long-term outcome of the dialysis patient.

Low-GDP fluid (Gambrosol trio) attenuates decline of residual renal function in PD patients: a prospective randomized study

BACKGROUND

Residual renal function (RRF) impacts outcome of peritoneal dialysis (PD) patients. Some PD fluids contain glucose degradation products (GDPs) which have been shown to affect cell systems and tissues. They may also act as precursors of advanced glycosylation endproducts (AGEs) both locally and systemically, potentially inflicting damage to the kidney as the major organ for AGE elimination. We conducted a clinical study in PD patients to see if the content of GDP in the PD fluid has any influence on the decline of the residual renal function.

METHODS

In a multicentre approach, 80 patients (GFF > or = 3 mL/min/1.732 or creatinine clearance > or =3 mL/min/1.73 m(2)) were randomized to treatment with a PD fluid containing low levels of GDP or standard PD fluid for 18 months. RRF was assessed every 4-6 weeks. Fluid balance, mesothelial cell mass marker CA125, peritoneal membrane characteristics, C-reactive protein (CRP), total protein, albumin, electrolytes and phosphate were measured repeatedly.

RESULTS

Data from 69 patients revealed a significant difference in monthly RRF change: -1.5% (95% CI = -3.07% to +0.03%) with low GDP (43 patients) vs -4.3% (95% CI = -6.8% to -2.06%) with standard fluids (26 patients) (P = 0.0437), independent of angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker medication. Twenty-four-hour urine volume declined more slowly with low-GDP fluid compared to standard fluids (12 vs 38 mL/month, P = 0.0241), and monthly change of phosphate level was smaller (+0.013 vs +0.061 mg/dL, P = 0.0381).

CONCLUSIONS

Our prospective study demonstrates for the first time a significant benefit concerning preservation of RRF and urine volume of using a PD fluid with low GDP levels. These findings suggest that GDPs might affect patient outcome related to RRF.

High levels of serum fibroblast growth factor (FGF)-23 are associated with increased mortality in long haemodialysis patients

BACKGROUND

Fibroblast growth factor (FGF)-23, a novel bone-derived phosphaturic factor involved in mineral metabolism, is increased in chronic kidney disease (CKD); in dialysis patients, it has been linked to increased mortality rates and vascular calcification (VC). The present investigation aimed to study the factors associated with elevated serum FGF-23 levels in patients treated with long haemodialysis (LHD) sessions and to determine whether a relationship exists between serum FGF-23 levels and patient survival.

METHODS

All patients treated in one haemodialysis centre from September 2006 were included in the study. Standard laboratory values, medical history, cardiovascular events and risk factors, medication and FGF-23 levels [ELISA (C-Term) Immutopics] were recorded. Patients received haemodialysis three times a week, on a 5- to 8-h schedule. Patient data were analysed according to FGF-23 quartiles. The effect of FGF-23 on the 2-year survival rate was assessed using the Cox proportional hazard model, adjusted for confounding variables and according to the serum phosphate tertiles.

RESULTS

The study included 219 patients. Serum FGF-23 levels were high: 7060 +/- 13 500 RU/mL (median, 2740 RU/mL). In logistical regressions, only calcaemia (P = 0.002), phosphataemia (P = 0.008) and warfarin use (P = 0.04) were associated with the highest FGF-23 quartile. In the subgroup of patients with an estimated VC score, the third and fourth quartiles of the FGF-23 levels were associated with more severe VC. In multivariate linear regressions, only phosphataemia remained significantly correlated with FGF-23 (P = 0.04). The 2-year mortality rate was significantly higher for haemodialysis patients with serum FGF-23 levels in the higher quartile [P = 0.007; hazard ratio, 2.5 (1.3-5)] than in the first quartile, whereas within the phosphataemia tertiles, the lowest serum FGF-23 quartile was associated with lowered mortality.

CONCLUSION

This study demonstrated a high level of circulating FGF-23 in LHD patients, despite infrequent hyperphosphataemia. However, phosphataemia is still the main factor correlating with serum FGF-23. The association of higher serum FGF-23 levels with mortality and VC, regardless of the serum phosphate levels, has thus been confirmed.

Peripheral vascular calcification in long-haemodialysis patients: associated factors and survival consequences

BACKGROUND

Vascular calcifications (VCs) are frequently observed in chronic kidney disease (CKD) and haemodialysis (HD) patients. They have been associated with numerous factors, particularly hyperphosphataemia, excess calcium load, hypertension and increased mortality rate. The purpose of this study is to measure VCs in long-HD patients with good blood pressure and phosphate control, with the occasional use of sevelamer, using a plain radiological score to identify the associated factors and effects on the 1-year survival rate.

METHODS

We studied HD patients from one centre using a semi-quantitative score ranging from 0 to 3 according to the severity and extent of VCs. The following patients' characteristics were compared according to their VC scores: medical history, treatments, blood pressure, standard biological data, fibroblast growth factor (FGF) 23, osteoprotegerin (OPG), whole PTH, beta-crosslaps, bone alkaline phosphatases and bone mineral density scores. One-year survival analyses were also performed.

RESULTS

Among the 250 HD patients of the centre, 161 were studied; the mean age was 67.2 +/- 13 years, 45% of the subjects were females, 35% were diabetics, and they had been on dialysis for between 1-486 months (median: 45 months) with a 3 x 5-3 x 8 h dialysis schedule using 1.5 mmol/l dialysate calcium and providing a mean 2.25 +/- 0.5 Kt/V. Only 17% of the patients were free from VCs and 11% had severe VCs. The factors associated with VCs were classified into 'classic' (age, diabetes, male gender, tobacco use, inflammation, more frequent warfarin treatment and peripheral vascular and cardiac diseases) and 'non-traditional' (higher FGF-23 and OPG serum levels, low albumin serum levels and low alfacalcidol and CaCO(3) use). In logistic regression, only age, diabetes and FGF-23 serum levels were associated with VC scores of 2 and 3. The patients with a score of 3 had a higher 1-year mortality rate (RR 2.1; P = 0.01) as compared to patients with a 0 score.

CONCLUSION

A plain radiological score showed the high prevalence (83%) of VCs in HD patients in spite of a long and intensive dialysis strategy and adherence to guidelines. The main associated factors were classic factors such as ageing and diabetes. No relationship was found with blood pressure and phosphataemia that remained well controlled in long dialysis; the association with FGF-23 serum levels may aggregate some non-traditional risk factors. The harmful effects of VCs on survival require their systematic assessment and optimization of the potentially modifiable associated factors in CKD and HD patients.

Phosphorus control in peritoneal dialysis patients

Hyperphosphatemia is independently associated with an increased risk of death among dialysis patients. In this study, we have assessed the status of phosphate control and its clinical and laboratory associations in a large international group of patients on chronic peritoneal dialysis (PD) treatment. This cross-sectional multicenter study was carried out in 24 centers in three different countries (Canada, Greece, and Turkey) among 530 PD patients (235 women, 295 men) with a mean+/-s.d. age of 55+/-16 years and mean duration of PD of 33+/-25 months. Serum calcium (Ca(2+)), ionized Ca(2+), phosphate, intact parathyroid hormone (iPTH), 25-hydroxy vitamin D(3), 1,25-dihydroxy vitamin D(3), total alkaline phosphatase, and bone alkaline phosphatase concentrations were investigated, along with adequacy parameters such as Kt/V, weekly creatinine clearance, and daily urine output. Mean Kt/V was 2.3+/-0.65, weekly creatinine clearance 78.5+/-76.6 l, and daily urine output 550+/-603 ml day(-1). Fifty-five percent of patients had a urine volume of <400 ml day(-1). Mean serum phosphorus level was 4.9+/-1.3 mg per 100 ml, serum Ca(2+) 9.4+/-1.07 mg per 100 ml, iPTH 267+/-356 pg ml(-1), ionized Ca(2+) 1.08+/-0.32 mg per 100 ml, calcium phosphorus (Ca x P) product 39+/-19 mg(2)dl(-2), 25(OH)D(3) 8.3+/-9.3 ng ml(-1), 1,25(OH)(2)D(3) 9.7+/-6.7 pg ml(-1), total alkaline phosphatase 170+/-178 U l(-1), and bone alkaline phosphatase 71+/-108 U l(-1). While 14% of patients were hypophosphatemic, with a serum phosphorus level lower than 3.5 mg per 100 ml, most patients (307 patients, 58%) had a serum phosphate level between 3.5 and 5.5 mg per 100 ml. Serum phosphorus level was 5.5 mg per 100 ml or greater in 28% (149) of patients. Serum Ca(2+) level was > or =9.5 mg per 100 ml in 250 patients (49%), between 8.5 and 9.5 mg per 100 ml in 214 patients (40%), and lower than 8.5 mg per 100 ml in 66 patients (12%). Ca x P product was >55 mg(2)dl(-2) in 136 patients (26%) and lower than 55 mg(2)dl(-2) in 394 patients (74%). Serum phosphorus levels were positively correlated with serum albumin (P<0.027) and iPTH (P=0.001), and negatively correlated with age (P<0.033). Serum phosphorus was also statistically different (P = 0.013) in the older age group (>65 years) compared to younger patients; mean levels were 5.1+/-1.4 and 4.5+/-1.1 mg per 100 ml, respectively, in the two groups. In our study, among 530 PD patients, accepted uremic-normal limits of serum phosphorus control was achieved in 58%, Ca x P in 73%, serum Ca(2+) in 53%, and iPTH levels in 24% of subjects. Our results show that chronic PD, when combined with dietary measures and use of phosphate binders, is associated with satisfactory serum phosphorus control in the majority of patients.

Pharmacological control of secondary hyperparathyroidism in chronic hemodialysis patients: cinacalcet is coming to Japan

Secondary hyperparathyroidism has a significant impact on morbidity and mortality due to skeletal and extraskeletal manifestations. Cinacalcet, a newly developed calcimimetic, is reported to decrease parathyroidism, as well as serum levels of phosphorus (P) and calcium (Ca) and therefore Ca x P product. Available evidence has shown that cinacalcet decreases the rate of parathyroidectomy and bone fracture in hemodialysis patients, but the death rate remains the same. Although, it is not yet available in Japan, cinacalcet is expected to be available as a possible drug for patients undergoing hemodialysis due to secondary hyperparathyroidism associated with refractory hyperphosphatemia and hypercalcemia. Except for the high cost, cinacalcet will be a welcome therapeutic option for end-stage renal disease and probably also for pre-end-stage renal disease patients. Dietary phosphate restriction and adequate hemodialysis, however, are still the main strategy for the control of hyperphosphatemia and secondary hyperparathyroidism.