Dietitian intervention may improve patients' ability to restrict their daily intake of phosphorus

 

IMPAIRED BONE mineral metabolism is prevalent in CKD patients, presenting a special challenge for patients and renal health professionals. By stage 5 CKD, an estimated 50% or more of dialysis patients have bone mineral parameters that exceed evidence-based practice guidelines. Newer pharmacologic treatments combined with dietary interventions show promise in normalizing serum phosphorus, calcium, and intact parathyroid hormone (iPTH) levels, with a goal of improving patient outcomes. Hyperphosphatemia and resulting secondary hyperparathyroidism (SHPT), which are common in hemodialysis patients (Block et al, J Am Soc Nephrol. 2004;15:2208-2218), are major contributors to CVD and all-cause mortality in CKD (Melamed et al, Kidney Int. 2006;70:351-357).

 

To assist renal health professionals in improving patient outcomes, the National Kidney Foundation (NKF) Kidney Disease Outcomes Quality Initiatives (K/DOQI) developed evidence-based recommendations, “K/DOQI clinical practice guidelines for bone metabolism and disease in chronic kidney disease” (Am J Kidney Dis. 2003;42:S1-S201). Regarding the importance of diet, K/DOQI clinical practice guidelines acknowledge that “it is critical to provide consistent and regular follow-up during prescription of dietary phosphate restriction while ensuring adequate protein intake.” Recommendations advise limiting phosphorus to 800-1,000 mg daily for serum levels greater than 5.5 mg/dL in stage 5 CKD or if above 4.6 mg/dL in earlier CKD stages, and for iPTH levels higher than 300 pg/mL.

 

Recognizing the need to improve phosphorus control—since “most data indicate that fewer than 30% of dialysis patients are able to maintain phosphorus in the suggested target range” of 3.5 to 5.5 mg/dL—K/DOQI suggests that “successful implementation will require an increased dietitian-to-patient ratio, educational tools to increase patient compliance, as well as studies to further explore the feasibility of dialytic techniques that are better able to control serum phosphorus levels (such as nocturnal or daily hemodialysis), and the widespread availability and affordability of different phosphate binders, regardless of patient insurance.”

 

An example of a dietitian-implemented intervention, “Improving phosphorus control: an intensive educational approach,” was presented by my colleagues and I at the ESRD Network of New England Annual Meeting in 2003. Results of the four-month study of 340 maintenance hemodialysis patients demonstrated that targeted interventions coordinated by registered dietitians (RD) consisting of individual patient instruction with weekly review, educational pamphlets (RD generated, and commercially available), visual presentations (bulletin boards, videos), displays of low phosphorus alternatives (“taste-test”), and phosphate binder reminders significantly improved patient knowledge (post-test vs. pre-test scores) and bone mineral parameters while maintaining adequate serum albumin (3.9 g/dL at both baseline and at four months) and stable dry weight (79.8 and 79.4 kg at baseline and at four months, respectively). Mean phosphorus im-proved from 5.7 mg/dL at baseline to 5.4 mg/dL at four months; iPTH decreased from 317.8 to 251.3 pg/dL. Mean serum calcium remained at an acceptable level (9.1 to 9.3 mg/dL). We concluded that intensive ongoing patient education contributes to improvements in bone metabolism for dialysis patients, with further study needed to examine the duration of results and impact on health outcomes.

 

Complicating dietary management of phosphorus is the growing presence of phosphate additives in processed foods. In addition to the usual high phosphorus foods (dairy products, nuts/seeds, whole grains, dried beans/peas, etc.), patients need to be informed of the “hidden” sources as outlined in a series of articles by Lisa Murphy-Gutekunst, MSEd, RD, CSR, and colleagues in the Journal of Renal Nutrition (2005;15[2-4]:e1-6,e1-6,e1-4). The authors noted that the increasing use of phosphate additives, which are absorbed more efficiently than phosphate from natural food sources (about 100% vs. 60%), “could now contribute up to 1,000 mg of phosphorus per day depending on an individual's food choices.” Since “nutrition facts” labels are not required to provide information about phosphorus content, consumers must be alerted to phosphate salt ingredients (monosodium and disodium phosphate, phosphoric acid, polyphosphates, pyrophosphates, etc.) in “enhanced” meats and other processed foods and beverages. Assisting CKD patients in choosing lower phosphorus foods is key to improving phosphorus control and achieving K/DOQI bone metabolism goals.

 

Approaches to phosphate management from a public health perspective are outlined in a recently paper by Ashwini R. Sehgal, MD, and colleagues in the Journal of Renal Nutrition (2008;18:256-264). In addition to the usual medical and dietary interventions, the authors suggest four public health measures to assist patients in achieving mineral metabolism goals.

 

These include:

• Media/public health messages about food (i.e., changes in advertising to encourage healthier choices)

• The availability of appropriate foods and medications (i.e., subsidies to promote healthier foods; better drug coverage)

• Physical structures such as the location of products in grocery stores (i.e., including tax incentives to draw grocers to poorer communities)

• Appropriate social structures such as food labeling laws (i.e., requiring phosphorus content on nutrition facts labels).