An accurate measurement of blood pressure (BP) is crucial when it comes to screening, diagnosing and treating hypertension, the leading cause of heart disease worldwide. In the United States, an estimated 1.3 million youth ages 12 to 19 have high blood pressure, or about 1 in 25 children, according to the U.S. Centers for Disease Control and Prevention.

But using a regular BP cuff for every patient, regardless of the patient’s mid-upper arm circumference, can lead to inaccurate automated readings, according to a recent study led by Tammy Brady, vice chair for clinical research in the Department of Pediatrics at Johns Hopkins Children’s Center. Results of the randomized crossover trial of 195 adults with a wide range of mid-upper arm circumferences were reported in JAMA Internal Medicine.

Brady and colleagues affiliated with Johns Hopkins’ Welch Center for Prevention, Epidemiology and Clinical Research, found that when people requiring a large or extra-large BP cuff were measured with a regular BP cuff, the device gave a significantly higher blood pressure reading, one that was almost 5 mmHg and 20 mmHg higher, respectively. In contrast, among people requiring a small BP cuff, a regular BP cuff resulted in blood pressure readings that were more than 3 mmHg lower than their actual BP.

Brady and her colleagues say these results support the conclusion that patients (and parents of children) should become familiar with what BP cuff size is appropriate and proactively ensure that size is used during each practitioner visit. Patients should also only use home blood pressure monitoring devices that provide a cuff that fits their arm.