(CNN)The next time you get your blood pressure taken at the doctor, you might consider asking the nurse to take it in both arms.
A significant difference in the systolic, or top blood pressure reading between the two arms could be a warning sign of a future heart attack or stroke, according to a new meta-analysis of 24 global studies published Monday in the journal Hypertension.7 steps that can lower your blood pressure as you age“Patients who require a blood pressure check should now expect that it’s checked in both arms, at least once,” said lead author Dr. Chris Clark, a clinical senior lecturer at the University of Exeter Medical School in the United Kingdom, in a statement.Blood pressure is measured in units of millimeters of mercury (abbreviated as mmHg), which consists of two numbers — an upper or systolic reading that represents the maximum amount of pressure in your arteries, and the lower or diastolic reading that shows the pressure in your arteries when your heart muscle is at rest between beats. The new study found that for each degree of difference between the two arms over 10 millimeters of mercury, the risk of having new angina (chest pain), a heart attack or a stroke increased by 1% over the next decade.Read MoreThe study results indicate that differences above 5 millimeters of mercury between two arms “predict all-cause mortality, cardio- vascular mortality and cardiovascular events.” “We’ve long known that a difference in blood pressure between the two arms is linked to poorer health outcomes,” Clark said. This study “tells us that the higher the difference in blood pressure between arms, the greater the cardiovascular risk, so it really is critical to measure both arms to establish which patients may be at significantly increased risk,” Clark said. Systolic differences the keyThe American Heart Association considers blood pressure normal when the top number is less than 120 and the bottom number is less than 80.A difference of 10 millimeters of mercury or less between arms is considered normal by the AHA and is not a cause for concern. However, higher readings between the two arms might be a sign of a narrowing or stiffening of the arteries, which can affect blood flow. Unlike guidelines in the US, those in both UK and the European Union recognize “a systolic difference of 15 mmHg or more between the two arms as the threshold indicative of additional cardiovascular risk,” the study said.Research coauthor Victor Aboyans, professor and head of the department of cardiology at the Dupuytren University Hospital in Limoges, France, said the study shows that international guidelines should be reevaluated.”We believe that a 10 mmHg difference can now reasonably be regarded as an upper limit of normal for systolic inter-arm blood pressure, when both arms are measured in sequence during routine clinical appointments,” Aboyans said in a statement. “This information should be incorporated into future guidelines and clinical practice in assessing cardiovascular risk. It would mean many more people were considered for treatment that could reduce their risk of heart attack, stroke and death,” Aboyans added.In addition, health practitioners should be measuring blood pressure in both arms at checkups, the report said. While international guidelines currently recommend that practice, it is “widely ignored.” “Whilst international guidelines currently recommend that this is done, it only happens around half of the time at best, usually due to time constraints,” Clark said.”Checking one arm then the other with a routinely used blood pressure monitor is cheap and can be carried out in any healthcare setting, without the need for additional or expensive equipment,” Clark said. “Our research shows that the little extra time it takes to measure both arms could ultimately save lives.”Taking your own blood pressureAnyone with concerns about their blood pressure should monitor it at home and keep a journal of the readings, the AHA suggests. The first step is to carefully choose a blood pressure cuff — the AHA recommends an automatic, cuff-style, upper-arm monitor — not a wrist or finger monitor — which are not as reliable. The AHA says to take blood pressure readings at the same time each day, such as morning or evening. Follow these steps to be sure that you get an accurate reading:Don’t smoke, drink caffeinated beverages or exercise for at least 30 minutes before measuring your blood pressure. Go to the bathroom and empty your bladder.Sit with your back straight and supported, which means sitting on a hard-backed chair at a desk or table, not a sofa. “Your feet should be flat on the floor and your legs should not be crossed. Your arm should be supported on a flat surface (such as a table) with the upper arm at heart level,” the AHA recommends.Get CNN Health's weekly newsletter
Sign up here to get The Results Are In with Dr. Sanjay Gupta every Tuesday from the CNN Health team.
Roll up your sleeve — don’t take the measurement over clothes. Sit there for at least five minutes of quiet rest before starting any measurements.Follow the illustrations on your blood pressure monitor — one key step is to be sure the bottom of the cuff is placed directly above the bend of the elbow. Take multiple readings and record the results. “Each time you measure, take two or three readings one minute apart, and record the results using a printable tracker. If your monitor has built-in memory to store your readings, take it with you to your appointments. Some monitors may also allow you to upload your readings to a secure website after you register your profile,” the AHA recommends.