Diagnostic Accuracy of Unattended Automated Office Blood Pressure Measurement in Screening for Hypertension in Kenya

Abstract

Despite increasing adoption of unattended automated office blood pressure (uAOBP) measurement for determining clinic blood pressure (BP), its diagnostic performance in screening for hypertension in low-income settings has not been determined. We determined the validity of uAOBP in screening for hypertension, using 24-hour ambulatory BP monitoring as the reference standard. We studied a random population sample of 982 Kenyan adults; mean age, 42 years; 60% women; 2% with diabetes mellitus; none taking antihypertensive medications. We calculated sensitivity using 3 different screen positivity cutoffs (≥130/80, ≥135/85, and ≥140/90 mm Hg) and other measures of validity/agreement. Mean 24-hour ambulatory BP monitoring systolic BP was similar to mean uAOBP systolic BP (mean difference, 0.6 mm Hg; 95% CI, -0.6 to 1.9), but the 95% limits of agreement were wide (-39 to 40 mm Hg). Overall discriminatory accuracy of uAOBP was the same (area under receiver operating characteristic curves, 0.66-0.68; 95% CI range, 0.64-0.71) irrespective of uAOBP cutoffs used. Sensitivity of uAOBP displayed an inverse association (P<0.001) with the cutoff selected, progressively decreasing from 67% (95% CI, 62-72) when using a cutoff of ≥130/80 mm Hg to 55% (95% CI, 49-60) at ≥135/85 mm Hg to 44% (95% CI, 39-49) at ≥140/90 mm Hg. Diagnostic performance was significantly better (P<0.001) in overweight and obese individuals (body mass index, >25 kg/m²). No differences in results were present in other subanalyses. uAOBP misclassifies significant proportions of individuals undergoing screening for hypertension in Kenya. Additional studies on how to improve screening strategies in this setting are needed.

Keywords: Kenya; adult; blood pressure; humans; hypertension.

Figure 1.

Study flowchart. Hypertension (HTN) on ambulatory blood pressure monitoring (ABPM) was defined as 24-h ABPM value ≥130/80 mm Hg. uAOBP indicates unattended automated office blood pressure.

Figure 2.

Bland-Altman plots showing levels of agreement between unattended automated office blood pressure (uAOBP) and ambulatory blood pressure monitoring (ABPM) measurements. A, Systolic; (B) diastolic. The correlation coefficients (Pitman test) between the difference and mean were r=−0.021, P=0.516 for systolic measurements and r=0.002, P=0.945 for diastolic measurements indicating no systematic proportional trend. Dashed horizontal lines indicate 95% limits of agreement. DBP indicates diastolic blood pressure; and SBP, systolic blood pressure.

Figure 3.

Scatter plot of ambulatory blood pressure monitoring (ABPM) vs unattended automated office blood pressure (uAOBP) values in study participants. Vertical dashed lines indicate the different systolic blood pressure (SBP)/diastolic blood pressure (DBP) cutoffs for screen positivity on uAOBP. A, SBP ≥140; (B) DBP ≥90; (C) SBP ≥135; (D) DBP ≥85; (E) SBP ≥130; (F) DBP ≥80. Horizontal dashed lines indicate cutoff for confirmed hypertension on ABPM. Data points in black indicate participants whose hypertensive status was correctly classified by uAOBP (ie, true positives and true negatives). Data points in red indicate false negatives (masked hypertension). Data points in blue indicate false positives (white coat hypertension). BP indicates blood pressure.