Background: Elevated serum phosphorus (P) and calcium-P product (CaXP) are associated with cardiac mortality in dialysis patients. A CaXP <55 is considered acceptable by most authorities. Because nutrition practices can modulate CaXP, we designed a survey to study the impact of the patients' levels of education and disease awareness on their CaXP.
Methods: A survey questionnaire with 5 didactic questions pertaining to hyperphosphatemia and P-binders and 5 questions related to patient attitudes and beliefs was administered to all patients in a hemodialysis unit. The association of CaXP >55 with the patients' level of education, their score on the survey (didactic part, score 0 to 5), parathyroid hormone (PTH) levels, hyperkalemia, hypertension, and vascular disease were studied.
Results: Of the 117 patients (61 men, age 56.5 +/- 18 years) who participated in the survey, 49 (42%) had CaXP >55 and 100 (85%) were on P binders. Thirty-seven (31.6%) had at least some college education. Eighty-seven patients (74%) failed to identify foods rich in P; 61% were unaware of complications related to high CaXP. Patients with CaXP >55 were less likely to have college education (20% versus 39%, P =.04), and had lower survey scores (2.4 +/- 1.3 versus 2.6 +/- 1.4, P = NS). Patients with college education scored higher (2.9 +/- 1.1 versus 2.3 +/- 1.4, P =.014). Furthermore, CaXP >55 was significantly associated with hyperkalemia (P =.02), high PTH levels (P <.001), and hypertension (P =.02), but not with >Kt/V, URR, type of hemodialysis access, or vascular diseases.
Conclusion: The majority of patients in the survey were ignorant of basic facts pertaining to high P and CaXP. The association of CaXP >55 with hyperkalemia, and not with Kt/V, suggests dietary noncompliance rather than inadequate dialysis. Patients with less education were more likely to have CaXP >55. Because this related mostly to misperception of simple facts that affect dietary habits, there is need for focused counseling of these patients at a level appropriate for their literacy skills.