Psychometric properties of perceived barriers to PKU treatment inventory in a Brazilian national sample

What is it about?

Phenylketonuria (PKU) is a lifelong metabolic condition in which strict dietary adherence is critical for maintaining metabolic control. However, various personal, social, economic, and health system–related obstacles can hinder adherence and thereby threaten optimal outcomes. In this study, we validate a 25‑item Perceived Barriers to PKU Treatment Inventory (in two versions: one for patients, one for caregivers) using a diverse Brazilian sample (n = 241 online, n = 42 in person) from 23 Brazilian states. The psychometric evaluation included internal consistency (KR‑20), convergent validity, known‑group validity, discriminant validity via ROC analyses, and a qualitative content analysis of open responses. Our key findings include: The inventory showed adequate reliability. Evidence of convergent validity emerged via negative correlations between barrier scores and self‐rated knowledge/adherence (measured by visual analogue scales). The instrument discriminated between risk groups for poor metabolic control (ROC curve), and optimal cutoffs were proposed for patients and for caregivers. Qualitative data revealed that socioeconomic constraints, system‑level issues, dietary burden, and social support gaps remain central barriers from both patient and caregiver perspectives. Interestingly, differences emerged between in‑person vs online responders, possibly reflecting social desirability bias or sample heterogeneity in disclosure of barriers.

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Why is it important?

Having a validated, brief screening tool to identify perceived barriers to PKU treatment is immensely useful in both clinical and research settings. It enables care teams to stratify risk, tailor interventions, and monitor changes over time in patients and their caregivers. It also underscores that, beyond medical prescription, psychosocial, economic, and systemic factors must be integrally addressed in rare disease adherence strategies.