Objective The study aims to investigate the variability in three blood pressure (BP) readings within one measurement (within-visit BPV) and the relevant influencing factors.

Methods Three BP readings were taken at 2-min interval in 2092 adults (1028 males and 1064 females) with mercurial sphygmomanometer. The average of three BP readings was used as the mean BP. The standard deviation (SD) of three BP readings and coefficient of variation (CV: SD/mean BP) were calculated for evaluating within-visit BPV. According to the history of hypertension and use of antihypertensive drugs, the participants were divided into hypertensive (EH group, 756 cases) and normotensive groups (NT group,). Multiple stepwise regression analysis was used to analyse the relevant influencing factors.

Results 1. A positive relationship existed between the mean SBP rank and SD(r = 0.168, P < 0.01) in the whole population. Although the SBP and SD were higher in EH group than in NT group, no significant difference of CV was found between two groups. 2. The SD and CV were significantly higher in females than in males although lower SBP in female. 3 Positive relationship was found between age rank and SD (r = 0.129, P < 0.01) and between age rank and CV (r = 0.153, P < 0.01), with stronger relationship in females (r = 0.137 and 0.166, both P < 0.05) than in males (r = 0.098 and 0.122, both P < 0.05).

Conclusions The mean SBP, female and ageing are related with higher within-visit SBP variability, but female and ageing are independent facilitating factors.