What PDC is
Proportion of Days Covered is a claims-based adherence measure. For a given medication over a measurement window, it divides the number of days the patient had the drug on hand (from fill and refill dates) by the total days in the window, expressed as a percentage.
The widely used threshold is 80%: a patient with a PDC at or above 80% for a chronic medication is considered adherent. PDC is calculated for high-impact drug classes such as statins, diabetes medications (RASA and non-insulin diabetes drugs), and blood-pressure medications, the same classes that appear as Medicare Star Ratings adherence measures.
PDC improves when patients refill on time. Rivvi runs refill and adherence outreach as real two-way conversations from a branded pharmacy number, reminding patients before they run out, resolving pickup and refill barriers, and honoring opt-out, so more patients stay above the 80% line.
PDC, answered
PDC divides the number of days a patient had a medication on hand (derived from prescription fill and refill dates) by the number of days in the measurement period, expressed as a percentage. It is computed per drug class and, when a patient takes multiple drugs in a class, uses the combined covered days.
A PDC of 80% or higher is the standard threshold for being considered adherent to a chronic medication. Medicare Star Ratings adherence measures count the share of eligible members who reach that 80% threshold for statins, diabetes medications, and blood-pressure medications.
PDC and the Medication Possession Ratio (MPR) both estimate adherence from fill data, but PDC counts covered days without letting overlapping early refills inflate the score above 100%, so it is more conservative. PDC is the measure CMS uses for Star Ratings adherence.
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