Different blood pressure readings from left and right arm may indicate increased risk of heart attack, stroke and death

While most people know of the harm both high blood pressure (hypertension) and low blood pressure (hypotension) can do to the body, many wouldn’t know that the smallest factors could alter blood pressure measurements. Of course, the calibration and handling of the blood pressure machine itself matter but so do individual factors like how your arm is placed or what your body position is.

Factors that affect your blood pressure readings

A study published in the Journal of Human Hypertension in 2003 explains that you get very different blood pressure measurements if the patient is sitting upright or straight, if the right arm is raised to around the level of the heart and if the patient is supine or lying down and the arms are resting on the side. A 2007 study in the Journal of Clinical Nursing suggests that your blood pressure levels are likely to be recorded as lower if you’re standing during the process instead of sitting or lying down.

While both studies note that this is why every physician and nurse should note the position of the body and the arm while recording the blood pressure, only the latter concludes that the best way to measure blood pressure is in a sitting position with the arms at the level of the heart. It’s important to note that it’s not just the body and arm positions that matter where your blood pressure is concerned, but also which arm you’re measuring.

Inter-arm differences in blood pressure

An article in Harvard Health Publishing explains that it’s normal to have different readings on different arms but a difference of more than 10 mmHg could indicate the presence of an underlying condition. In younger people, it could suggest that an artery is compressed or there’s a structural problem in blood flow. In older people, it could indicate the emergence of atherosclerosis and aortic dissection.

A study published in the BMJ in 2012 further suggests that dissimilarity in blood pressure readings on different arms by 10-15 mmHg is a sign that you have circulatory problems that can increase the risks of stroke, peripheral artery disease and other cardiovascular issues.

Another study - this time an Indian one on 1,634 adults in Tamil Nadu - published in the Journal of Family Medicine and Primary Care in 2018 explains that these inter-arm differences in blood pressure measurements can range a lot depending on the age or risk factors of the population involved. Those who have hypertension already, smoke, abuse alcohol and are overweight or obese tend to have inter-arm differences above 10 mmHg, sometimes even above 15mmHG. This clearly shows that measuring the inter-arm differences in blood pressure at every examination can indicate if a person has a higher risk of cardiovascular and blood circulatory disorders.

A large study on inter-arm differences

A new study published in the journal Hypertension confirms the findings of these earlier studies and adds that such inter-arm differences in blood pressure measurements can ultimately increase your risk of mortality too. The new study, led by researchers at the University of Exeter, is an observational one that includes data from 24 global studies from the Inter-arm Blood Pressure Difference - Individual Participant Data (INTERPRESS-IPD) Collaboration. These studies provided descriptive records of bilateral blood pressure and its outcomes in 53,827 participants.

The researchers found that inter-arm differences of even 5 mmHg in systolic blood pressure measurements (which is the top number as opposed to the diastolic or bottom number) were found to be associated with a higher risk of all-cause mortality (hazard ratio or HR of 1.05) and cardiovascular mortality (HR of 1.06). This HR for all-cause mortality increased as the inter-arm difference increased above 5 mmHg. Even in people without a pre-existing disease, this threshold of difference in inter-arm measurements indicates a higher risk of cardiovascular events like angina, heart attack and stroke.

This study, therefore, concludes that it’s the inter-arm difference between systolic measurements that better indicate higher disease risks. The researchers ultimately found that a difference of 10 mmHg is the upper limit of normal inter-arm differences in blood pressure measurements, but even a difference of a few mmHg should not be ignored. In fact, blood pressure should be measured in both arms during a proper cardiovascular disease risk assessment.

For more information, read our article on High blood pressure.

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