The dietary counseling given to maintenance dialysis patients may be inadequate
DESPITE regular dietary instruction, patients undergoing dialysis have a poor knowledge of die-
tary phosphorus compared with other nutrients important in CKD, according to researchers at the
University of WisconsinMedicalSchool in Madison.
Judson B. Pollock, MD, and Jonathan B. Jaffery, MD, studied 29 hemodialysis (HD) patients and 18 peritoneal dialysis (PD) patients. The study population consisted of 30 men and 17 women and had an average age of 58.6 years. All patients received once-monthly dietary instruction customized by a dietitian based on each patient's laboratory data and fluid-volume status.
The researchers measured nutrient knowledge using a 25-item Chronic Kidney Disease Know-ledge Assessment Tool for Nutrition (CKDKAT-N). This questionnaire has 25 multiple choice questions reflecting knowledge of four nutrients relevant to maintenance dialysis patients: phosphorus, protein, sodium, and potassium. Fif-teen questions concern phosphorus. Drs. Pollock and Jaffery also measured functional health literature using the short form of the Test of Functional Health Literacy in Adults (S-TOFHLA). S-TOFHLA is a 36-item test that involves short reading passages with multiple-choice answers. It is administered in seven minutes. Results are scored on a scale of 0-36, with 0-16 iden-tifying inadequate health literacy, 17-22 marginal health literacy, and 23-36 adequate health literacy.
The mean CKDKAT-N scores for the HD and PD groups were 12.5 and 14, respectively, a nonsignificant difference, the authors reported in the Journal of Renal Nutrition (2007; published online ahead of print).
Among HD patients, the S-TOFHLA ranking showed that 18 had adequate health literacy, whereas four had marginal and seven had inadequate literacy. Among PD pa-tients, 17 had adequate health literacy and one had inadequate literacy. HD and PD patients had an average of 0.8 and 2.4 years of post-secondary education, respectively, a significant difference between the groups.
The study population overall correctly answered only about 38% of phosphorus-related questions, whereas they correctly answered about 71% of questions related to protein, sodium, and potassium. Despite differences in education level and health literacy between the HD and PD groups, the group had similar nutrition knowledge.
The authors concluded: “The mounting evidence that individual education, adequate health literacy, and dialysis modality do not translate into an improved knowledge of dietary phosphorus suggests that the current standard of dietary consultation by nephrologists, dialysis nurses, and renal dietitians, coupled with judicious phosphate-binder prescription, may not be adequate to overcome this complex problem.”
Drs. Pollock and Jaffery observed that hyperphosphatemia remains common in maintenance dialysis patients despite widespread awareness of the increased morbidity and mortality associated with elevated serum phosphorus levels. They noted that in the DOPPS cohort from 1996 to 2001, 52% of patients had phosphorus levels about the target range even though 81% of subjects were treated with binder medications.
Other studies also show widespread ignorance of phosphorus in the dialysis population. For instance, in a study of 117 dialysis patients, Rajiv D. Poduval, MD, and colleagues found that 74% of them failed to identify foods rich in phosphorus and 61% were unaware of complications related to high calcium-phosphorus product, according to a paper published in the Journal of Renal Nutrition (2003;13:219-223).
Some studies suggest that educational counseling may be effective in helping patients control phosphorus intake. For example, Adamasco Cupisti, MD, and colleagues showed that HD patients with hyperphosophatemia (serum phosphorus above 5.5 mg/dL) decreased dietary phosphorus and calcium intake, and had improved calcium-phosphate product after intensive dietary intervention and counseling. Their study included 43 stable adult HD patients, 20 of whom had hyperphosphatemia. A dietitian performed individual assessments of dietary habits for all patients. The hyperphosphatemia patients had individual dietary counseling, including education about which foods provide less phosphorus while preserving the same protein (favorable phosphorus-to-protein ratio). The patients received information about food processing, with special attention paid to foods containing extra phosphorus as an additive. Preferable food choices and recipes were proposed, taking into account patients' dietary habits and lifestyle to lower the distress caused by dramatic changes, which could negatively affect compliance, the authors noted. Investigators reinforced verbal counseling using printed materials containing information on high- and low-phosphorus foods, as well as recipe examples when required.
Phosphate and calcium intake decreased significantly by 100 mg on average but dietary protein did not change. Serum calcium-phosphate product decreased significantly from 66.8 to 61 mg2/dL2; serum phosphate showed a nonsignificant trend to decrease.