Measuring blood pressure accurately

SUMMARY

Accurately measuring blood pressure is imperative for diagnosis and control of hypertension.

There is a range of devices and methods for measuring blood pressure that each have advantages and limitations.

To ensure accuracy of blood pressure measurement and hypertension diagnosis, clinicians and patients should use an accurate and validated blood pressure measurement device, an appropriately sized cuff, and take several measurements rather than only one measurement, using a standardised measurement protocol.

Out-of-clinic measurement, using an ambulatory or home blood pressure monitoring device, depending on patient preference, should be used to confirm diagnosis and guide treatment of hypertension.

There are emerging new technologies for blood pressure measurement (e.g. wearable technologies) that are yet to be validated and have the potential to improve blood pressure monitoring and patient self-management.

 

Introduction

Hypertension is a leading modifiable risk factor for cardiovascular disease (including heart attack and stroke), kidney disease, pregnancy complications and cognitive decline. Further, the risk of cardiovascular complications and death has been shown to be linked to the level of blood pressure.¹ Controlling hypertension is associated with improved health outcomes and reduced mortality.² Accurate measurement of blood pressure is imperative for diagnosis and management of hypertension; however, despite emphasis in guidelines, in busy daily clinical practice there is often a lack of standardised protocol.^3,4 This article will discuss the different methods and devices available for measuring blood pressure, both in and out of clinical settings, as well as other factors that influence accurate measurement, ways to optimise measurement, and self-monitoring.

 

Methods of measuring blood pressure

There is a range of ways to measure blood pressure. While intra-arterial measurement is the only direct method of measuring blood pressure, and is used in critical care settings, it is not transferable to routine clinical practice. There are currently 2 main indirect methods for measuring blood pressure:

• The auscultatory technique has been used for many years. It involves an upper arm cuff, a sphygmomanometer, and a stethoscope to listen for blood flow in the artery (Korotkoff sounds); this method requires specific training. Due to environmental and safety concerns, mercury-containing devices have been replaced by aneroid sphygmomanometer devices.
• Devices using the oscillometric technique are usually electronic and automatically inflate and deflate the cuff. They measure mean blood pressure and then estimate systolic and diastolic blood pressure using a manufacturer-specific algorithm. Although measuring blood pressure is easier with oscillometric devices, there is still a need for standardised protocols and understanding their limitations.⁵ For patients with an irregular heart rhythm or who are pregnant, it is important to verify blood pressure measurements using the auscultatory technique.

Easily accessible websites, such as STRIDE BP and VALIDATE BP, provide information for health professionals and patients to confirm which devices have been validated and are accurate when used and maintained correctly.

All measurement devices, including validated devices, need to be calibrated regularly to ensure that measurements are reliable. Validation refers to the initial process of verifying that the device is measuring accurately and complies with international standards. Ongoing device calibration is required to maintain accuracy; this can only be performed by the manufacturer. The recommended intervals for calibration are determined by the manufacturer, usually yearly or every 2 years.

Table 1 summarises the different approaches to blood pressure measurement and their advantages and limitations.

Table 1 Advantages and limitations of different approaches to measuring blood pressure

Method	Advantages	Limitations
Random (one-off) clinic blood pressure measurement	Fast, minimal preparation	Low reproducibility; may trigger white coat effect (temporary increase in blood pressure due to anxiety in a clinical setting)
Standardised clinic blood pressure measurement	Multiple readings, using a protocol and a validated measurement device has better accuracy and reproducibility; key method used in clinical trials to predict cardiovascular outcomes	Training required; protocol requires dedicated time, which busy clinics may find challenging
Automated oscillometric office blood pressure measurement	Multiple readings taken, often unattended, which reduces observer bias and white coat effect; reproducibility correlates with daytime ambulatory blood pressure monitoring if a protocol is used	Specific monitoring device required; need to ensure device is validated and regularly calibrated; nonadherence to measurement protocol may lead to measurement error
Ambulatory blood pressure monitoring	Provides a 24-hour blood pressure profile during daily activities and sleep; identifies hypertension phenotype [NB1]; strongest predictor of cardiovascular outcomes	Some patients may find this type of device uncomfortable, and it may interfere with sleep; availability may be limited; potential for measurement error due to lack of patient adherence to instructions
Home blood pressure monitoring	Easy to use; enables monitoring of blood pressure away from clinic; encourages self-management	Measures blood pressure only at rest; usually lacks nocturnal measurement; potential for measurement error due to lack of adherence to a protocol or use of a non-validated device
NB1: Hypertension phenotype refers to different patterns or classifications of blood pressure elevation. Examples of hypertension phenotypes that can be detected with out-of-clinic blood pressure monitoring include: white coat hypertension (where blood pressure is elevated only when measured in clinical settings); masked hypertension (where blood pressure is elevated only when measured in nonclinical settings); and nocturnal or 'non-dipping' hypertension (absence of a nocturnal 'dip' in blood pressure, which is a pattern associated with increased cardiovascular risk).

 

Factors that affect accuracy of blood pressure measurement

As well as the need to use validated and calibrated devices, there are many factors that impact accuracy of blood pressure measurement and diagnosis of hypertension,including cuff size, patient position and comfort, the site of measurement, and single versus multiple measurements.^3,4,6 These are summarised in Table 2.

Table 2 Factors that impact accuracy of blood pressure measurement

Factor	Underestimates BP	Overestimates BP
Cuff size too small		✔
Cuff size too large	✔
Crossed legs		✔
Talking during measurement		✔
Unsupported back		✔
Position of arm on lap rather than supported		✔
Device not calibrated	✔	✔
Patient not rested before measuring blood pressure		✔
Failure to check that both arms give comparable readings at initial visit	✔	✔
Feeling cold		✔
Ingestion of coffee or alcohol within 30 minutes before measurement		✔
Urinary bladder distension		✔
Taking a single measurement	✔	✔

A common barrier to accurate measurement is not selecting an appropriately sized arm cuff.⁷ Using a cuff that is too big can underestimate blood pressure. Using a cuff that is too small overestimates blood pressure. Cuff size should be selected according to instructions from the manufacturer. The markings on the cuff can be used as a guide, or the mid-upper arm circumference can be measured (Figure 1A). Typically, bladder width should be at least 40% of the circumference of the upper arm and bladder length 80 to 100% of arm circumference (Figure 1B). Some devices now include single 'wide-range' cuffs, which are designed to fit a range of arm circumferences. A conical-shaped cuff should be used for individuals with upper arm circumference greater than 42 cm, as a regular cuff may overestimate blood pressure. If blood pressure cannot be measured with an upper arm cuff, a validated electronic wrist-cuff monitor may be used.

Talking to the patient while measuring their blood pressure can increase systolic pressure by 4 to 19 mmHg and diastolic pressure by 5 to 14 mmHg.⁶ Positioning of the arm on the patient's lap or unsupported by their side during measurement, rather than supported on a desk, results in substantially overestimated blood pressure.⁸

Measuring blood pressure in both arms at the first visit and using the arm with the higher measurement enhances the accuracy of diagnosing hypertension. Systolic interarm difference of 5 mmHg or more is associated with increased cardiovascular and all-cause mortality.⁹ Using measurements from the arm with lower blood pressure can lead to misdiagnosis and lack of follow-up. A recent study identified interarm blood pressure differences to be more prevalent in women.¹⁰

 

Blood pressure measurement in clinical settings

Blood pressure measured in clinical settings has been the key method for defining thresholds for diagnosis of hypertension and monitoring efficacy of treatment, as well as in research for predicting future cardiovascular events. Due to white coat effect (elevated blood pressure when measured by a health professional, especially on first measurement), it is important to record several measurements in the clinic using standardised procedures (Box 1) to confirm the patient's blood pressure.¹¹ Of note, women experience white coat effect more often than men.^12,13

Automated office blood pressure measurement devices are recommended for use in clinical settings and are programmed to record measurements at set intervals, an average of which is displayed. While automated office blood pressure devices may reduce variability in measurement and minimise human errors, there is still a need for a standardised measurement protocol and training. Further information on automated office blood pressure measurement can be found in the recent consensus statement by Hypertension Australia and the National Hypertension Taskforce of Australia.¹⁴

Sex differences in blood pressure

It is increasingly recognised that only measuring brachial (upper arm) blood pressure in women may not identify their risk of cardiovascular disease, as it may lack accuracy in estimating aortic blood pressure. Studies have reported that the brachial cuff adequately estimated aortic blood pressure in men but lacked accuracy in women, who had higher aortic systolic blood pressure at similar brachial cuff systolic blood pressure.^15,16 Measurement of blood pressure waveform provides insight into these differences; young women and men did not have differing pulse pressure and pressure waveform between mean arterial pressure (MAP) levels;¹⁷ however, there was greater age-related reduction in the ability to buffer pulse pressure with increasing MAP in women of reproductive age, starting at least a decade earlier than men. Although not in standard practice, a validated oscillometric device that provides measurement of central and brachial blood pressure, and pulse pressure waveform analysis using a standard upper arm cuff (the Uscom BP+), is available for in-clinic use.

Ambulatory and home blood pressure measurement

Best practice for diagnosis of hypertension is to confirm in-clinic blood pressure measurements with out-of-clinic measurement, either ambulatory or home monitoring,¹⁸ depending on device availability and patient preference. Out-of-clinic measurement provides a better indicator of the patient's blood pressure, including identifying different phenotypes of hypertension, as well as more accurately indicating response to treatment (Table 1).

Ambulatory blood pressure monitoring (ABPM) has an important role in clinical practice,^19,20 providing measurements during the patient's activities across the daytime as well as during sleep. ABPM can be used to confirm a diagnosis of hypertension and to monitor efficacy of treatment. It is usually performed over 24 hours with measurements programmed typically every 15 to 20 minutes during the day and every 20 to 30 minutes during sleep. The threshold for hypertension in adults using ABPM for daytime is greater than or equal to 135/85 mmHg and for night-time is greater than or equal to 120/70 mmHg. In addition to identifying white coat hypertension (consistently elevated in-clinic but normal out-of-clinic blood pressure) and masked hypertension (normal in-clinic but elevated out-of-clinic blood pressure), ABPM can identify nocturnal hypertension (absence of physiological decrease in blood pressure, referred to as nocturnal dipping) which independently predicts future cardiovascular complications.²¹ ABPM also identifies important sex differences in blood pressure regulation, with women having greater variability than men and greater prevalence of white coat hypertension.²²

The availability of Medicare reimbursement for ABPM (MBS Item 11607) supports accessibility in primary care. A guide to ABPM was developed by the National Heart Foundation and High Blood Pressure Research Council of Australia Ambulatory Blood Pressure Monitoring Consensus Committee.²³

Home blood pressure monitoring (HBPM) is convenient and comparable to ABPM for accuracy provided a validated device is used with a correctly sized cuff. The diagnostic threshold for hypertension is greater than or equal to 135/85 mmHg. It is important to inform the patient that many home devices on the market have not been independently validated for accuracy even though they have passed safety standards.²⁴ Patients can access information about which devices are validated and approved on the STRIDE BP and VALIDATE BP websites. Patients need to be educated about a standardised protocol to ensure accurate measurement.²⁵ The recommendation is to measure blood pressure after a 5-minute rest period, with the arm and back supported, taking two measurements 1 minute apart. Measurements should be conducted morning and evening for at least 3, and ideally, 7 days.

Cuffless devices and other new technologies are accelerating to meet consumer demands to self-monitor blood pressure. Devices include wrist monitors, rings and smartphones. These devices have the potential to provide continuous, noninvasive blood pressure measurement during daily activities; however, their accuracy has not yet been confirmed since there are currently no recognised validation standards. Therefore, these devices cannot currently be used for clinical diagnosis and management of hypertension. Similarly, artificial intelligence and machine learning are rapidly advancing and have potential for enhancing accurate blood pressure measurement and personalised treatment. Currently, there are several challenges that need to be addressed before these can be implemented into clinical practice. Further research is required to ensure accuracy and validation, data privacy and inclusion of diverse demographic groups.²⁶

 

Conclusion

Accurate measurement of blood pressure using standardised protocols must be a priority for clinicians, despite the demands of busy clinical practices, to improve the clinical diagnosis and treatment of hypertension. Whichever method is used, the foundations are the same – using a measurement device that is validated, following a standardised protocol, using an appropriately sized and shaped cuff, taking several measurements, and being aware of sex differences. This will support greater accuracy in diagnosis of hypertension and blood pressure monitoring, ensure a personalised approach and promote greater self-efficacy in managing hypertension.

This article was finalised on 26 February 2026

Conflicts of interest: Anastasia Mihailidou is on the Scientific Advisory Board for STRIDE BP. She has received honoraria from Medtronic for providing education seminars.

This article is peer reviewed.

 

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