Biochemical detection and psychosocial correlates of antihypertensive adherence in hypertension: initial observations from a cross-sectional study in two Irish tertiary care centres

Background

Non-adherence to antihypertensive drugs (AHDs) contributes to poor blood pressure (BP) control, yet self-reported adherence measures are unreliable. Chemical adherence testing (CAT) using liquid chromatography–high resolution mass spectrometry (LC-HRMS) provides objective assessment, but integration with psychosocial profiling is limited.

Purpose

We aimed to determine the prevalence and patterns of antihypertensive non-adherence using CAT and explore associated psychosocial, clinical and demographic characteristics in specialist hypertension clinics. We hypothesised that CAT-defined non-adherence would be associated with patient-level psychosocial characteristics.

Methods

In this prospective cross-sectional study, 171 consecutive patients attending two Irish tertiary hypertension centres underwent unannounced spot urine CAT. Participants completed validated measures of self-reported adherence (MARS-5), beliefs about medicines (BMQ), health literacy, anxiety and depression (HADS), and patient–provider communication. Absence of ≥2 prescribed AHDs defined clinically significant non-adherence. Univariable Firth penalised logistic regression was used due to sparse events.

Results

Only 2/171 participants self-reported non-adherence. CAT detected all prescribed AHDs in 132 (77%), partial detection in 32 (19%), and none in 7 (4%). Among 145 participants prescribed ≥2 agents, 10 (7%) were missing ≥2 agents.

Self-reported adherence and MARS-5 scores did not differ between groups. No demographic predictors were identified.

Indifference (55%) and acceptance (39%) were the most common BMQ profiles. Compared with the Accepting group, the Sceptical group had higher odds of non-adherence (OR 20.56, 95% CI 2.27–265.82; p=0.008). Higher depression scores were also associated with non-adherence (OR 1.17 per unit increase; 95% CI 1.01–1.36; p=0.03). Health literacy, anxiety, illness coherence and perceived physician communication were not associated with adherence.

Non-adherent participants had higher unadjusted mean office SBP (156 vs 136 mmHg; p<0.005) and higher mean 24-hour ambulatory SBP (166 vs 132 mmHg; p=0.017). Amlodipine showed 96% detection (n=75), while nebivolol had the lowest detection (55%, n=11).

Conclusion

Biochemically confirmed non-adherence was not identified by self-report and was unrelated to demographic factors. Depressive symptoms and sceptical medication beliefs were associated with CAT-detected non-adherence and higher BP. To our knowledge, the association between an attitudinal belief profile and objectively measured non-adherence has not previously been described in CAT-based hypertension cohorts. Integration of biochemical and psychosocial assessment may help identify patients who could benefit from targeted adherence interventions.