Systolic Blood Pressure and Biochemical Assessment of Adherence

Elevated blood pressure (BP) is common in the emergency department (ED), but the relationship between antihypertensive medication adherence and BP in the ED is unclear. This cross-sectional study tested the hypothesis that higher antihypertensive adherence is associated with lower systolic BP (SBP) in the ED among adults with hypertension who sought ED care at an academic hospital from July 2012 to April 2013. Biochemical assessment of antihypertensive adherence was performed using a mass spectrometry blood assay, and the primary outcome was average ED SBP. Analyses were stratified by number of prescribed antihypertensives (<3, ≥3) and adjusted for age, sex, race, insurance, literacy, numeracy, education, body mass index, and comorbidities. Among 85 patients prescribed ≥3 antihypertensives, mean SBP for adherent patients was 134.4 mm Hg (±26.1 mm Hg), and in adjusted analysis was −20.8 mm Hg (95% confidence interval, −34.2 to −7.4 mm Hg; P =0.003) different from nonadherent patients. Among 176 patients prescribed <3 antihypertensives, mean SBP was 135.5 mm Hg (±20.6 mm Hg) for adherent patients, with no difference by adherence in adjusted analysis (+2.9 mm Hg; 95% confidence interval, −4.7 to 10.5 mm Hg; P =0.45). Antihypertensive nonadherence identified by biochemical assessment was common and associated with higher SBP in the ED among patients who had a primary care provider and health insurance and who were prescribed ≥3 antihypertensives. Biochemical assessment of antihypertensives could help distinguish medication nonadherence from other contributors to elevated BP and identify target populations for intervention.