Evaluating the Accuracy of an Aneroid Sphygmomanometer in a Clinical Trial Setting

BACKGROUND: The mercury sphygmomanometer, the "gold" standard for blood pressure measurements, has been gradually phased out in many institutions because of environmental concerns. Our on-going clinical trial compared the use of mercury vs. aneroid sphygmomanometers, before implementing a study-wide transition to the aneroid sphygmomanometer. METHODS: The Diabetes Prevention Program Outcomes Study (DPPOS) studied the accuracy of the Welch Allyn Tycos 767-Series Mobile aneroid sphygmomanometer from 20 March 2006 to 21 June 2006 at multiple clinic centers. We compared readings from 997 participants in 24 clinic centers using both mercury and aneroid sphygmomanometers. RESULTS: The study found no statistically significant difference for systolic blood pressure (SBP) (P > 0.05) and a small but significantly (P < 0.0001) lower (0.8 mm Hg) reading for diastolic blood pressure (DBP) using the aneroid sphygmomanometer. Regression analysis of aneroid vs. mercury showed regression lines (Y = 4.8 + 0.96X for SBP, Y = 3.1 + 0.95X for DBP) slightly but statistically significantly different from the line of equality (P < 0.001). Participants' age, sex, race/ethnicity, body mass index, blood pressure, and clinical center together explain about 8-10% of the variation of the difference between readings from the two sphygmomanometers. Based on the above result, on 1 August 2006, DPPOS clinics began the conversion from mercury to aneroid sphygmomanometers. CONCLUSIONS: The Welch Allyn Tycos 767-Series Mobile Aneroid model 7670-04 tested in this validation study can be used to replace mercury model in clinical trials.