High but not low self-reported statin adherence was confirmed by a novel method based on plasma-statin measurements in coronary outpatients
Authors: Kristiansen O , Sverre E , Peersen K , Fagerland MW , Gjertsen E , Gullestad L , Perk J , Dammen T , Husebye E , Vethe NT , Munkhaugen J 
Published: May 2021

Funding Acknowledgements

Type of funding sources: Public hospital(s). Main funding source(s): Helse Sør-Øst

Background

To what extent self-reported adherence measures correspond with directly measured statin adherence is unknown.

Purpose

 To determine the relationship between, self-reported adherence measures, low density lipoprotein-cholesterol (LDL-C) and directly measured statin adherence in coronary outpatients.

Methods

Patients on atorvastatin (N = 373) participated in a cross-sectional study median 16 months after a coronary event. Adherence to statins the past 7 days, general medication adherence assessed by the 8-item Morisky medication adherence scale (MMAS-8), and the Gehi adherence question was obtained by a self-report questionnaire. Atorvastatin was determined in spot blood plasma samples by a novel liquid-chromatography tandem mass-spectrometry method discriminating between adherence (0-1 doses omitted) and reduced (≥2 doses omitted) adherence. Participants were unaware of the atorvastatin analyses at study participation. 

Results

Mean age was 63 (SD 9) years and 19% were females. Mean atorvastatin dose was 64 (SD 21) mg. The number with reduced adherence by the different measurement methods, Cohens kappa agreement score between the self-reported and direct adherence measures, and LDL-C are shown in the Table. Statin adherence was confirmed by the direct method among 96% reporting high statin adherence the past 7 days, among 95% reporting high adherence on the MMAS-8 and among 94% reporting high adherence on the Gehi adherence question. In contrast, among patients classified with reduced statin adherence by the direct method, only 40% reported reduced statin adherence the past week, 32% reported reduced adherence with the MMAS-8 and 22% with the Gehi adherence question.

Conclusions

The direct method confirmed high, but not low, self-reported statin adherence in this selected sample of coronary outpatients. In patients with elevated LDL-cholesterol, plasma-statin measurements emerges as a potential improvement for clinical statin management.

Adherence measures and LDL cholesterol Directly measured atorvastatin adherence Self-reported statin adherence past 7 days Self-reported medication adherence past month (Gehi) 8-item Morisky medication adherence scale Number with reduced adherence, % 7.8 5.5 3.0 8.4 Cohen"s kappa (95% CI) Reference 0.4 (0.2 to 0.6) 0.3 (0.1 to 0.5) 0.2 (0.1 to 0.4) LDL-C, Adherent, mean (95% CI) 1.9 (1.8 to 1.9) 1.9 (1.8 to 2.0) 1.9 (1.8 to 2.0) 1.9 (1.8 to 1.9) LDL-C, Reduced adherence, mean (95% CI) 2.8 (2.4 to 3.2) 2.8 (2.3 to 3.2) 3.2 (2.5 to 3.8) 2.1 (1.9 to 2.4) LDL-C, Adherent versus reduced adherence P &lt;0.001 P = 0.001 P = 0.004 P = 0.07 Agreement between directly measured atorvastatin adherence, self-reported measures of adherence, and mean low density lipoprotein-cholesterol (LDL-C)