Exploring the implications of different approaches to estimate centre-level adherence using objective adherence data in an adult cystic fibrosis centre - a retrospective observational study.

ABSTRACT

BACKGROUND: Accurate centre-level medication adherence measurement allows identification of highly performing CF centres, drives shared learning and informs quality improvement. Self-reported adherence is unreliable but data-logging nebulisers can capture objective data. However, adherence levels in current literature are limited by the use of agreed prescriptions and convenience sampling. In this single-centre retrospective study, we quantified the differences in centre-level adherence with different methods of calculating adherence (unadjusted vs normative adherence) and different data sampling frames (convenience sampling vs including difficult to obtain data). METHODS: Adherence data were objectively captured using I-neb® from 2013-2016 in Sheffield Adult CF Centre. Adults on non data-logging devices, on ivacaftor or with previous lung transplantation were excluded. Adherence was calculated based on agreed regimen ('unadjusted adherence') or minimum required regimen ('normative adherence'). I-nebs® not brought to clinic were downloaded during home visits. Adults not on any inhaled therapy but with chronic Pseudomonas aeruginosa infection were included by counting their adherence as "0". RESULTS: Of the 131 included adults, 126 provided I-neb® data. Calculating unadjusted adherence from I-nebs® brought to clinics resulted in the highest centre-level adherence (median 41.8% in 2013). Median adherence reduced after sequentially accounting for minimum required regimen (40.0% in 2013), I-nebs® not brought to clinics (32.9% in 2013) and adults not on any inhaled therapy (31.0% in 2013). CONCLUSIONS: Different approaches of calculating adherence produced different adherence levels. Adherence levels based only on agreed regimen among adults who readily brought their nebulisers to clinics can over-estimate the effective adherence of CF centres.