In order to receive comparable results, the environment should be standardised as much as possible [10]. The technique is accurately described in the National Institute for Health Care Excellence (NICE) and European Society of Hypertension (ESH) guidelines [10] and summarised in the following:

The patient should be rested and relaxed in a seated position for at least 3–5 min and rested before beginning BP measurements [7, 10]. The arm is out-stretched, in line with the mid-sternum and supported [10]. Further requirements for the environment are shown in Table 4. An appropriately sized cuff (as indicated by markings, see also the paragraph on Cuffs) is wrapped around the upper arm and connected to a manometer [10]. While palpating the brachial pulse, the cuff is rapidly inflated to 20 mmHg above the point where the brachial pulse disappears [10]. This pressure should be noted, as it is the approximate systolic pressure [10]. The cuff should then be re-inflated to 20 mmHg above this point [10]. The stethoscope should be placed over the brachial artery ensuring complete skin contact without clothing in between [10]. Then, the cuff is slowly deflated at 2–3 mmHg per second listening for the Korotkoff sounds [10]. The first sound appearing with the brachial pulse (phase I Korotkoff sound) is the systolic pressure [10]. At this point, the pulse pressure wave overcomes the obstruction caused by the cuff with its maximal pressure [10]. Intermediate sounds follow as the cuff pressure drops, with muffling and then complete disappearance of sounds (phase V Korotkoff sounds) indicating the diastolic pressure [10]. At this point the residual diastolic arterial pressure is sufficient to overcome the pressure caused by the cuff, leading to a normal arterial diameter without systolic blood flow murmurs [10]. The cuff is then quickly deflated completely [7, 10]. At least two BP measurements should be taken in the sitting position, spaced 1–2 min apart, adding more measurements if the first two are quite different (in daily practice more than 2–5 mmHg difference) and the average of the measurements should be used [7]. More measurements are recommended in patients with arrhythmia (i.e. atrial fibrillation) [7]. In case of elevated OBPM, the diagnosis of hypertension should be confirmed in a second visit, usually 1–4 weeks after the initial investigation or preferably with the use of ABPM [10, 15, 16].

In case of a significant (>10 mmHg) and consistent systolic BP difference between the arms, the arm with the higher BP values should be used [7]. A BP difference of >10 mmHg may help to identify patients in need of further vascular assessment, whereas a BP difference of ≥ 15 mmHg may be an indicator of peripheral vascular disease, pre-existing cerebrovascular disease, increased cardiovascular mortality and increased all-cause mortality [17].

BP is maintained through a combination of mechanical, neuronal and endocrine self-regulating systems in the body [10]. There is a considerable variability of BP due to respiration, emotion, exercise, meals, tobacco, alcohol, temperature, bladder distension, etc. [18]. Additionally, BP is influenced by age, race, and circadian variation [18]. Therefore attention should be paid to these circumstances.

A cuff is an inelastic cloth that encircles the arm and encloses an inflatable rubber bladder [18]. Present-day cuffs consist of an inflatable cloth-enclosed bladder which encircles the arm and is secured by Velcro or by tucking in the tapering end [10]. The width of the bladder is recommended to be about 40 %, and its length 80 % of the arm circumference [10]. Both cuffs that are too narrow and cuffs that are too short will lead to falsely high BP measurements [19]. A bladder which is too large will lead to an underestimation of BP [18]. Recommended cuff sizes are stated in Table 5 [20]. Arm cuffs are preferred, as cuffs fitting on the finger or wrist are often inaccurate and should therefore not be recommended [15].

There is a range of manual and automatic BP measurement devices available. For clinical decision making devices need to be validated according to standardised protocols and their accuracy should be checked on a regular basis through calibration in a technical laboratory [7, 21]. A list of currently recommended devices can be found online [22].

OBPM has been the cornerstone of hypertension diagnosis and management for over 100 years and is the basis for most studies on hypertension [27]. Even the most recent BP outcome studies like the SPRINT trial and the HOPE-3 trial rely on OBPM with specific measurement procedures in each study [28, 29]. Elevated OBPM predicts cardiovascular events (Fig. 2) [30]. Automated OBPM means to take the mean of multiple BP readings recorded with a fully automated device with the patient resting quietly, alone, in the office or clinic, which was reported to deliver results closer to ABPM [31].

A single office BP reading does not represent a patient’s true BP [32]. Errors may be due to patients’ alerting reaction to the measurement procedure and setting (i.e. white coat effect). With OBPM there is a lack of relevant information on BP during usual daytime activities and during sleep [32].

There is a high variability with a mean difference of approximately +20 mmHg sBP between OBPM measurements of primary care physicians and specifically trained research assistants, even after short training [33]. Possible pitfalls in daily practice may be faulty position such as legs crossed, back or arm unsupported, talking during the measurement or insufficient number of readings [33]. The influence of different pitfalls is summarised in Table 6.