Self-Motivation Is Associated With Phosphorus Control in End-Stage Renal Disease

Objective

Hyperphosphatemia is common in end-stage renal disease and associates with mortality. Phosphate binders reduce serum phosphorus levels; however, adherence is often poor. This pilot study aims to assess patients' self-motivation to adhere to phosphate binders, its association with phosphorus control, and potential differences by race.

Design and Methods

Cross sectional design. Subjects were enrolled from one academic medical center dialysis practice from July to November 2012. Self-motivation to adhere to phosphate binders was assessed with the autonomous regulation (AR) scale (range: 1-7) and self-reported medication adherence with the Morisky Medication Adherence Scale. Linear regression models adjusting for age, sex, health literacy, and medication adherence were applied to determine associations with serum phosphorus level, including any evidence of interaction by race.

Results

Among 100 participants, mean age was 51 years (±15 years), 53% were male, 72% were non-white, 89% received hemodialysis, and mean serum phosphorus level was 5.7 ± 1.6 mg/dL. More than half (57%) reported the maximum AR score (7). Higher AR scores were noted in those reporting better health overall (P = .001) and those with higher health literacy (P = .01). AR score correlated with better medication adherence (r = 0.22; P = .02), and medication adherence was negatively associated with serum phosphorus (r = −0.40; P < .001). In subgroup analysis among non-whites, higher AR scores correlated with lower serum phosphorus (high vs lower AR score: 5.55 [1.5] vs 6.96 [2.2]; P = .01). Associations between AR score (β 95% confidence interval: −0.37 [−0.73 to −0.01]; P = .04), medication adherence (β 95% confidence interval: −0.25 [−0.42 to −0.07]; P = .01), and serum phosphorus persisted in adjusted analyses.

Conclusions

Self-motivation was associated with phosphate binder adherence and phosphorus control, and this differed by race. Additional research is needed to determine if personalized, culturally sensitive strategies to understand and overcome motivational barriers may optimize mineral bone health in end-stage renal disease.

Introduction

Hyperphosphatemia is a component of chronic kidney disease that is associated with mineral and bone disorders¹ and has been linked to poor outcomes among patients receiving dialysis.² Racial and ethnic disparities exist in the treatment of end-stage renal disease (ESRD),³ and hyperphosphatemia is more common and more severe in non-whites compared to whites.⁴ Hyperphosphatemia can be effectively managed through diet and medication treatments,² but the management is often limited by poor adherence.⁵

Nonadherence in ESRD is associated with increased morbidity and mortality6, 7, 8; however, its importance is often underestimated. Nonadherence in the ESRD population ranges from 22% to 74% and affects all areas of phosphorus management self-care.⁹ Modifiable psychosocial factors have been identified as predictors of nonadherence to phosphate binders⁵ and include depressive symptoms,10, 11 medication beliefs,¹² and knowledge.13, 14

Another potential key factor is a person's sense of autonomous regulation (AR).¹⁵ Patients who view medication adherence as positive are more likely to participate in the behavior.¹⁶ A positive attitude has been shown to be one of the key factors that lessens the burden of treatment and improves adherence in complex patients with chronic conditions.¹⁷ When patients are empowered to make their own health behavior choices, and these positive health behaviors are aligned with the patient's attitude about the behavior, these changes are more likely to persist.¹⁵ In addition to attitudes, self-determination theory includes persons' self-efficacy to perform the behavior as well as their perception of their provider's support (Fig. 1). Patient characteristics including age, sex, and race may influence attitudes. Examining these factors may assist in our understanding of adherence to phosphate binder therapy.

The objective of this pilot study was to examine dialysis subjects' self-motivation to adhere to phosphate binder medication therapy and its association with medication adherence and also phosphorus control. We hypothesized that dialysis subjects with higher AR scores would report higher adherence to their phosphate binders and also have lower serum phosphorus levels. Racial influences on these measures were also examined. We hypothesized that self-motivation to adhere to phosphate binders would differ between white and non-white subjects.