CARDIOVASCULAR DISEASES Difference in blood pressure readings with mercury and automated devices: impact on hypertension prevalence estimates in Dar es Salaam, Tanzania

Abstract. Objectives: (1) To compare blood pressure (BP) readings with an automated arm cuff oscillo-metric device (AutoBP) to readings with a mercury sphygmomanometer (HgBP) and (2) to evaluate the impact on the prevalence of hypertension (HBP) in a population-based survey. Methods: (1) In a conve-nience sample (‘‘Comparison Study’’), we mea-sured BP with both AutoBP (Visomat OZ2) and HgBP and we modeled BP difference (DBP = HgBP)AutoBP) with multiple regression analysis. (2) Using DBP, we calculated HgBP in a survey previously conducted in Dar es Salaam (‘‘Population Survey’’) in which BP was measured with the automatic device Visomat OZ2 and we compared the prevalence of HBP (‡140/90 mmHg or treatment). Results: In the Comparison Study (404 subjects aged 25–64), systolic/diastolic BP was higher by 4.4/4.7 mmHg (SE: 0.4/0.3) with HgBP than AutoBP. The prevalence of HBP was 42 % with HgBP and 36 % with AutoBP (relative difference of 14%). DBP was associated with age, BP and arm circumference. In the Population Survey (9.254 sub-jects aged 25–64), the prevalence of HBP was 17% with calculated HgBP and 14 % with AutoBP (rela-tive difference of 20%). Conclusion: A small system-atic bias in BP readings between two different devices had large impact on hypertension prevalence esti-mates. This suggests that automated devices used in epidemiological studies should be validated with particular care