Quality Essentials Review: Evaluating Persistence to Basal Insulin

The PQA Quality Essentials Webinar seriesprovides education on the fundamentals of quality measurement, which is important for effective measure implementation and performance, and information about where and how PQA quality measures are used. 

In the October 20, 2022, PQA Quality Essentials Webinar Rachel Digmann, PharmD, PQA’s Senior Director of Performance Measurement, and Ben Shirley, CPHQ, PQA’s Director of Performance Measurement provided an overview of the history and development of PQA's Persistence to Basal Insulin (PST-INS) measure. Lynn Pezzullo, RPh, CPEHR, CPHQ, PQA's Senior Director of Quality Innovation, served as moderator for the webinar.   

The Persistence to Basal Insulin (PST-INS) measure was endorsed by PQA membership in 2020 and measures the percentage of individuals 18 years or older who were treatment persistent to basal insulin during the measurement year. 

Shirley opened the webinar by explaining how PST-INS was developed to meet a specific need for quality measurement related to insulin, as a noticeable gap exists in federal programs. Additionally, he noted that PQA’s diabetes adherence measure, Proportion of Days Covered – Diabetes All-Class (PDC-DR), excludes individuals using insulin due to the unreliability of the days’ supply field on prescription claims for insulin. 

PQA convened a multistakeholder roundtable to identify potential methodologies for measuring insulin persistence in 2016 and conducted an internal analysis to validate an approach developed by Wei et al. in a 2014 publication. Insulin persistence, as defined by this methodology, was found to be associated with reduced hemoglobin A1C and lower healthcare utilization and costs, outcomes which were reaffirmed by PQA’s own analyses. A measure concept based on this methodology was then developed through PQA’s consensus-based process following initial feasibility testing.  

Shirley went on to clarify the difference between adherence, which is assessed in numerous other PQA measures, and persistence. Adherence measured by proportion of days covered (PDC) captures the extent to which an individual has medication on hand during a treatment period. On the other hand, persistence refers to continuing a treatment for a defined duration; by measuring persistence, one can identify whether or not a patient has discontinued therapy during a given period. 

Digmann then introduced the PST-INS measure specifications. The eligible population includes individuals 18 years or older with at least one prescription claim for basal insulin during the measurement year and a treatment period of at least 91 days. A treatment period is defined as the time from an individual’s index prescription start date to the end of the measurement year. Individuals with gestational diabetes, end-stage renal disease, hospice care, or at least one prescription claim for mixed insulin or regular U-500 insulin during the measurement year are excluded.  

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To qualify for the measure numerator, an individual must have continued use of basal insulin throughout their treatment period. This continued use, or persistence, is determined when all refills for basal insulin occur on or prior to their expected refill dates. A reference table is used to estimate days’ supply based on the type of basal insulin and quantity dispensed; the reference table is empirically derived using a representative dataset from a broad population.  

PST-INS is intended to be used in a health plan performance program. As such, a program administrator would create the reference table using data from all plans and then utilize it to calculate measure rates for individual plans. The resulting estimated days’ supply is then used to determine a prescription’s expected refill date following a dispensing event. 

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Digmann walked attendees through an example of how a reference table is used to estimate days’ supply, determine expected refill dates, and compare actual refill dates to expected dates to evaluate whether an individual is persistent to basal insulin. 

Shirley and Digmann addressed frequently asked questions about the reference table used in PST-INS, including the methodology needed to generate the table and the reason for its use in the measure. The two went on to answer additional questions submitted by attendees related to how the measure considers patients who switch between types or strengths of insulin, and further clarified details about the reference table. Individuals were also referred to the PQA Technical Assistance form for additional questions. 

You can listen to the full recording of this Quality Essentials Webinar, a one-hour presentation with audience Q&A, on PQA’s YouTube channel. PQA members can access the presentation slides in the Member Resources Library.  

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