Why Medication Adherence Measurement Could Be Misleading for Your Practice

Understanding Medication Adherence Metrics: A Critical Overview

Medication adherence is pivotal for effective healthcare, particularly in chronic disease management, and the most widely recognized metric for gauging adherence is the Proportion of Days Covered (PDC). The Centers for Medicare & Medicaid Services (CMS) uses PDC as a cornerstone for quality ratings related to various chronic conditions such as diabetes and hypertension. Recent findings by Zheng et al. (2026) challenge the reliability of PDC measures, particularly regarding the date parameters used to calculate this important metric.

Does the Date Matter? A Deeper Dive

As revealed in the research, the timing of adjudication (the point when a claim is billed) might not accurately align with when a patient truly begins using their medication. The discrepancies become especially evident with systems implementing automatic refills or those utilizing mail-order pharmacies. Patients are unlikely to begin their medication on the same day it is filled. Furthermore, delays between the prescription being written and filled can significantly cloud the clarity of adherence metrics. Zheng’s paper highlights staggering statistics: nearly 25% of new chronic prescriptions are not filled within a week, and only 81% are filled within 30 days. This raises the question: does the choice of date—prescribing date, filling date, or selling date—affect the accuracy of adherence assessments?

The Two Faces of PDC: Exposure vs. Adherence

Zheng et al. introduce an important differentiation between two PDC definitions: the standard Exposure PDC and the revised Adherence PDC, the latter of which adjusts for significant treatment gaps. For instance, if a patient has a substantial gap in medication fills—120 days—in which the maximum allowable gap (MaxGap) is set at 90 days, only the duration exceeding the MaxGap will count as a non-adherent gap. This adjustment can notably influence adherence readings. Their study, which examined Surescripts data from between 2009 and 2019, underscores varying results for these two measures. While the Exposure PDC showed a range in adherence scores from a median of 0.747 to 0.794, with significant variability leading to misclassification of over 15% of patients using written dates, the Adherence PDC consistently revealed elevated adherence rates between 0.959 and 0.977—indicating that traditional metrics may not tell the whole truth.

Implications for Concierge Medical Practices

For medical professionals, particularly those in concierge practices focused on personalized care, understanding the nuances of medication adherence measurement can prove beneficial. As these practices thrive on delivering superior service and optimized patient care, insights drawn from Zheng’s analysis could empower practice owners to implement better adherence tracking and patient management strategies.

Implementing comprehensive methods that incorporate both Adherence PDC assessments alongside patient interviews and self-reported adherence metrics can provide a holistic view of medication compliance among patients. Such approaches minimize the risk of relying solely on retrospective pharmacy data, thereby enhancing patient care quality.

Looking Forward: A Call to Action

In light of the evidence presented, it becomes increasingly crucial for concierge medical practices to deepen their understanding of medication adherence metrics. By adopting a multi-faceted approach regarding adherence assessments, physicians can not only avoid pitfalls that misclassify patient compliance but also enrich the health outcomes for their clientele. Engaging patients with educational outreach regarding their medications, the importance of adherence, and accurate self-reporting practices will prove essential in fostering better health outcomes that align with best practices in healthcare management.