Difference in blood pressure readings between arms
It is vital to check blood pressure in both arms to detect differences, which are markers for increased cardiovascular risk
When considering a diagnosis of hypertension, the National Institute for Health and Clinical Excellence (2011) recommends measuring blood pressure in both arms. If the difference in readings between arms is more than 20mmHg, the measurement should be repeated. If the difference in readings between arms remains more than 20mmHg on the second measurement, measure subsequent blood pressures in the arm with the higher reading.
Box 1. commentary
NICE guidance on the management of primary hypertension recommends that we measure blood pressure in both arms and use the arm with the higher readings for consistency.
This primary-care cohort study demonstrates that if there is a significant difference in pressure between arms, this is a marker for increased peripheral vascular disease and cardiovascular risk. The findings from this small study are confirmed by the meta-analysis of 20 trials in which the increased risk was present when the difference in systolic blood pressure was more than 10mmHg, and increased further when the difference was 15mmHg. It was also present with differences in diastolic pressure.
This data provides important pointers to a potentially simple test to identify people at increased cardiovascular risk, but there is no evidence to recommend a treatment or management strategy at this stage. However, smoking cessation and lipid management would clearly be important steps.
This meta-analysis reinforces the advice from NICE to check the blood pressure in both arms, not just for consistency and accuracy, but also to detect a difference, which is a marker of increased cardiovascular risk.
A UK-based primary-care cohort study of 230 people receiving treatment for hypertension assessed whether a difference in systolic blood pressure readings between arms can predict a reduced event-free survival after 10 years (Clark et al, 2012a).
Results showed that a difference in systolic blood pressure of more than 10mmHg or 15mmHg between arms was associated with an increased risk of cardiovascular and all-cause mortality over 10 years. The risk of death was also increased in 183 participants without pre-existing cardiovascular disease, which seems to point to a level of risk for events of similar magnitude to that of participants with previously diagnosed cardiovascular disease.
These results were confirmed in a systematic review and meta-analysis of 20 studies, which investigated whether background difference in systolic blood pressure between arms of 10mmHg or more or 15mmHg or more, is associated with central or peripheral vascular disease (Clark et al, 2012b).
The results of the meta-analysis showed that a difference of 15mmHg or more was associated with increased risk of peripheral vascular disease, pre-existing cerebrovascular disease, and cardiovascular mortality and all-cause mortality. The risk of peripheral vascular disease was also increased at a difference of 10mmHg or more.
The researchers suggest that a difference in systolic blood pressure of 10mmHg or more or 15mmHg or more between arms could identify patients at high risk of asymptomatic peripheral vascular disease and mortality, who might benefit from further assessment - that is, bilateral brachial measurement, targeted screening for peripheral vascular disease and aggressive risk-factor management. The arm with the higher pressure can vary between individuals and it is the difference that counts, not which arm is higher and which is lower.
Further research is needed to establish the upper limit of normal between-arm differences, particularly for diastolic measurements.
Kathryn E Griffith is general practitioner with a special interest in cardiology, York; Carmel Thomason is senior publishing manager, evidence resources, National Institute for Health and Clinical Excellence
Adapted from Eyes on Evidence (November 2012), a bulletin produced by the National Institute for Health and Clinical Excellence. Reproduced with permission.
Clark CE et al (2012a) The difference in blood pressure readings between arms and survival: primary care cohort study. British Medical Journal; 344: e1327. tinyurl.com/BP-both-arms
Clark CE et al (2012b) Association of a difference in systolic blood pressure between arms with vascular disease and mortality: a systematic review and meta-analysis. Lancet; 379: 9819, 905-914.
National Institute for Health and Clinical Excellence (2011) Hypertension: Clinical Management of Primary Hypertension in Adults. tinyurl.com/NICE-CG127
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