Patient-Reported Factors Associated With Poor Phosphorus Control in a Maintenance Hemodialysis Population

Abstract

The purpose of this study was to determine the influence of patient-reported medication adherence and phosphorus-related knowledge on phosphorus control and pharmacy-reported adherence to phosphorus binding medication among patients on maintenance hemodialysis. Retrospective, cross-sectional cohort study. Seventy-nine hemodialysis patients (mean age 64.2 years, SD = 14 years; 46.8% female) in a stand-alone hemodialysis unit within an integrated learning healthcare system. Ten percent (10%) of subjects were Caucasian, 42% Latino, 19% African American, and 29% Asian. Forty-eight percent had diabetes; 72% had BMI ≥ 30. Inclusion criteria included the provision of survey data and having medication refill data available in the pharmacy system. 77.2% had mean phosphorus levels ≤ 5.5 mg/dL; 22.8% had mean phosphorus levels > 5.5 mg/dL. Subjects were administered the 8-item Morisky Medication Adherence Scale (MMAS-8) and also reported on their phosphorus-related knowledge. Phosphorus levels within an adequate range. The mean serum phosphorus level was 4.96 mg/dL (SD = 1.21). In the well-controlled group, mean phosphorus was 4.44 mg/dL (SD = 0.76). In the poorly controlled group, mean phosphorus was 6.69 mg/dL (SD = 0.74). A total of 61% of patients reported at least some unintentional medication nonadherence, and 48% reported intentional medication nonadherence. Phosphorus-specific knowledge was low, with just under half of patients reporting that they could not name two high-phosphorus foods or identify a phosphorus-related health risk. Phosphorus binder-related nonadherence was substantially higher in the uncontrolled than the controlled group. Adjusting for age, individuals with poorer self-reported binder adherence were less likely to have controlled phosphorus levels (odds ratio = 0.71, P = .06). Phosphorus-related non-adherence, but not low phosphorus-specific knowledge, was associated with poorer phosphorus control. Such findings provide important information for the development of evidence-based strategies for improving phosphorus control among patients on dialysis.