The Association Between Prescribed Dietary Phosphate Restriction and Mortality Among Hemodialysis Patients
To determine the relationship between prescribed dietary phosphate restriction and mortality among hemodialysis patients.
Study Design and Study Population
This is a post-hoc analysis of the Hemodialysis (HEMO) Study which was selected because it is one of the few large-scale prospective studies among dialysis patients in which dietary prescription was recorded. Data was available for 1751 patients and prescribed dietary phosphate was recorded at baseline and annually thereafter.
Intervention or Observation
The primary purpose of the HEMO Study was to test the effects of dialysis dose and dialytic membrane flux on clinical outcomes. This post-hoc analysis is an observational study of survival related to daily phosphate intakes of £ 870, 871-999, 1000, 1001-2000 mg and no restriction with a median followup time of 2.3 years. There were 817 deaths and a total of 4690 patient years at risk.
Primary and Secondary End-Points
Primary: Survival and all-cause mortality related to prescribed phosphate intake.
Secondary: Comorbidity, Kt/V, serum albumin, phosphate, corrected calcium and PTH levels. Anthropometric data, normalized protein, catabolic rate, appetite assessment and nutritional supplements completed the nutritional evaluation.
Statistics: Marginal structural proportional hazard models were fit to estimate the adjusted association between dietary phosphate restriction and mortality in the setting of time-dependent confounding.
The major conclusion is that prescribed dietary phosphate restriction is not associated with improved survival among prevalent hemodialysis patients once adjustments are made for a multitude of variables.
There is no correlation with serum phosphate and the precise use of phosphate binders was not available in this study although used extensively.
It appears that an increased level of restriction may be associated with greater mortality in some subgroups (eg. females, blacks and dialysis via a graft). Better survival and a more permissive prescribed dietary phosphate appeared in nonblacks, patients with a serum phosphate < 5.5 mg/dl and those not taking Vitamin D.
Hyperphosphatemia is common among hemodialysis patients with conventional hemodialysis and prescribed dietary phosphate restriction is recommended by KDIGO but on the basis of a 2d recommendation ie. weak recommendation with very low quality of evidence.
Previous publication of observational studies appear to support an increased mortality with rising levels of serum phosphate and there is evidence that the use of phosphate binders is associated with better survival.
The data for phosphate binders in this study is incomplete and serum phosphate levels showed no relationship to survival.
The relationship of phosphate to survival in hemodialysis patients is complex and this study appears to refute the assumption that prescribed dietary phosphate restriction leads to improved serum phosphate levels and better survival.
Phosphate restriction may be associated with protein malnutrition and inadequate caloric intake. The source of phosphate may also be important and inorganic phosphates added to processed foods as preservatives may have little or no impact on adequate nutrition.
Reviewed by Reviewed by Dr. Paul Barre