5 tips to remember when measuring blood pressure
Several factors can affect a blood pressure measurement and it is important to be aware of them. This article gives clinicians 5 tips to minimise their impact in the clinic and at home for patients.
- Observer/subject issues can cause blood pressure variability
- Using the correct cuff size in clinic and at home is important
- All blood pressure monitors in clinic and at home should be calibrated
- Be aware of the deflation rate of blood pressure monitors
- Minimise the risk of inaccuracy from wrist blood pressure monitors
See our summary of key points from NICE’s guideline on hypertension for further information on the diagnosis and management of hypertension.
Join OnMedica to access more clinical summaries
|Observer/ measurement issues||Subject/ biological issues|
When a blood pressure measurement in the clinic or in the home, standardise the environment and provide a relaxed, temperate setting, with the person quiet and seated, and their arm outstretched and supported.1 Muscle contraction in an unsupported arm can raise diastolic blood pressure by as much as 10% while raising the arm above heart level leads to an underestimation by as much as 10mmHg.2
- Undercuffing (either too narrow or too short a bladder) can lead to an overestimation of blood pressure.2
- Overcuffing (too wide or too long a bladder) can lead to an underestimation of blood pressure.2
- The Medicines and Healthcare products Regulatory Agency (MHRA) standard considers the optimum bladder size to be:
- a width of 40% of limb circumference,
- length 80% to 100% of limb circumference at the centre of the range for each cuff size.3
- The British and Irish Hypertension Society (BIHS) have a list of validated machines to be used both in clinic and at home, which includes cuff sizing.4
- The MHRA recommends twice annual calibration for aneroid sphygmomanometers and as per manufacturer’s recommendations for automated devices.2,3In primary care, this can be organised in house when other equipment is checked.
- It is important to remind patients that to have continued accuracy of their home devices, these also need to be calibrated and to contact the manufacturer to arrange for this to be done.
Join OnMedica to access more CPD resources
- Deflation should be at a rate of 2 mmHg/ second or 2 mmHg per beat if the patient has bradycardia.5
- BIHS looks at deflation speeds when validating automated blood pressure monitors.
Wrists blood pressure monitors are readily available to buy be the public and are relatively cheap. However, there is concern regarding the accuracy of these devices.
- The MHRA states that the readings are dependent on the relative positioning of the wrist to the heart and are less accurate than upper arm devices.3
BIHS concurs by explaining that wrist monitors are in the home validation list because they fulfil the accuracy criteria when strict attention is paid to the wrist position being at heart level, but this may not happen at home, therefore the measurement can become inaccurate.4
- Health professionals can minimise this risk of inaccuracy by recommending upper arm devices for home use.
References – 5 tips to remember when measuring blood pressure
- Hypertension in adults: diagnosis and management. NICE NG136, 2019
- Measuring blood pressure: top 10 tips. MHRA, 2013.
- Blood pressure measurement devices Blood pressure measurement devices. MHRA, 2021
- BP monitors. British and Irish Hypertension Society.
- Cahan A, et al. Association of Heart Rate With Blood Pressure Variability: Implications for Blood Pressure Measurement. American Journal of Hypertension, Volume 25, Issue 3, March 2012, Pages 313–318.