24-h ambulatory blood pressure monitoring (24-h ABPM) data collection procedure

The 24-h ABPM were conducted by a trained study nurse using a validated monitor (OSCAR 2, SunTech Medical) during routine school days²⁰. The monitor was programmed using AccuWin Pro 4 software to obtain BP measurements every 15 min for 24 h²⁰. Mid-upper arm circumference was used to determine the appropriately sized cuff, which was placed on a non-dominant arm and connected to the battery powered ABPM monitor using rubber tubing. Then we started the monitor and confirmed that it was functioning by observing two consecutive readings before allowing the participant to leave. After 24 h, we removed the ABPM monitor and downloaded the data. Sleep and wake times were defined using participant’s diary as recommended for adolescents⁴³. At least 20 and 7 readings during day and night respectively were required for a valid 24-h ABPM test. Height, gender and age were factored in to obtain the participant’s BP category. Times when participants were active or distressed were noted and used to interpret results. Pre-specified 24-h ABPM characteristic were extracted to data collection forms for double data entry using Open Clinica version 3.1.4. Participants with high BP using 24-h ABPM were regarded as having a confirmed diagnosis and counseled on diet and lifestyle changes and their BP were followed up during the study (if they had pre-hypertension) OR referred to specialist care (if they had hypertension)¹⁸.