Clinical Practice Guidelines for Bone Metabolism and Disease in Chronic Kidney Disease: An Overview

George R. Bailie, PharmD, PhD, FCCP; Shaul G. Massry, MD

Disclosures

Pharmacotherapy. 2005;25(12):1687-1707. 

In This Article

Guideline 4: Restriction of Dietary Phosphorus in Patients with Chronic Kidney Disease

Guideline Statements

4.1 - Dietary phosphorus should be restricted to 800-1000 mg/day (adjusted for dietary protein needs) when the serum phosphorus concentrations are elevated to greater than 4.6 mg/dl (1.49 mmol/L) at stages 3 and 4 of CKD (O), and greater than 5.5 mg/dl (1.78 mmol/L) in those with kidney failure, stage 5 (E).

4.2 - Dietary phosphorus should be restricted to 800-1000 mg/day (adjusted for dietary protein needs) when the plasma concentrations of iPTH are elevated above the target range for the CKD stage (E) ( Table 3 ).

4.3 - Serum phosphorus concentrations should be monitored every month after the start of dietary phosphorus restriction (O).

Association of Serum Phosphorus Concentration with Glomerular Filtration Rate

Pharmacists should understand the relationship between changes in plasma PTH and serum phosphorus concentrations, and decreasing GFR. Serum phosphorus concentrations in patients with CKD remain within or close to the normal range or until the GFR declines to 20-30 ml/minute/1.73 m2 (stage 4 CKD). Therefore, it may appear at first consideration that dietary phosphorus intervention is not necessary in patients with CKD stages 1, 2, or 3. However, phosphorus retention occurs early in the course of CKD (perhaps as early as stage 1) and participates in the development of secondary hyperparathyroidism. Parathyroid hormone concentrations in blood become elevated when GFR decreases to 60 ml/minute/1.73 m2, and the plasma PTH concentration is a better marker in the early course of CKD for the need to begin dietary phosphorus restriction than is serum phosphorus concentration. Serum calcium and creatinine concentrations may also remain relatively unaltered in the early stages of CKD; therefore, they also are unsuitable as early markers. By stages 4 and 5, serum phosphorus concentrations are elevated, and the need for dietary phosphorus restriction becomes obvious.

Dietary Phosphorus Control

Consistent instruction and regular follow-up during prescription of dietary phosphorus restriction is critical. In patients with early stages of CKD (stages 2 and 3), compliance with dietary phosphorus restriction is difficult and requires intensive support. Community pharmacists may well have a role to play in helping to improve dietary restrictions, since they tend to have frequent encounters with patients with CKD. Compliance with dietary phosphorus restriction in clinical practice is believed to be in the range of 35-91%.[9,20] Pharmacists in the community setting may be in a position to provide regular and routine counseling and provide written instruction about foods that have high phosphorus content. In patients with advanced CKD (stages 4 and 5), restriction of dietary phosphorus is more easily accomplished because concomitant dietary protein restriction (< 0.6 g/kg/day) may often be prescribed. A suitable source listing the phosphorus content of foods may be found at the United States Department of Agriculture National Nutrient Database for Standard Reference (http://www.nal.usda.gov/fnic/foodcomp/Data/SR16-1/wtrank/16-1w305.pdf).

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