Getting checked for hypertension, or high blood pressure, is often as simple as going to the doctor’s office for a quick measurement. However, there’s always a chance of “white coat hypertension,” or cases in which a person’s blood pressure is higher at the doctor’s office than outside, creating a false positive. And the opposite of that can occur as well.

Known as masked hypertension, undetected high blood pressure is often subtle and hidden, and doesn’t appear when tested at the doctor’s office. In a new study out of the American Heart Association, researchers experimented to see if around-the-clock monitoring could better identify masked hypertension than regular doctor visits. They found that a wearable device tracking blood pressure consistently throughout the day was a more effective tool for finding hidden blood pressure issues.

In the study, the researchers had participants wear a monitor day and night. The tool included a compact cuff for the arm that connected to a device at the hip. Compared to regular blood pressure monitoring, which is taken at different points throughout the day, the device could track blood pressure constantly while the wearer was sleeping, running, washing dishes, and doing other activities.

The researchers examined 317 African-American people, 69 percent of whom were women, from the Jackson Heart Study. At the beginning of the study, none of the participants had been diagnosed with high blood pressure, and they were tracked for eight years. At the end of the trial, 187 of them had developed high blood pressure. The authors found that individuals whose masked hypertension was detected by the wearable device were significantly more likely to later be diagnosed with high blood pressure at the doctor’s office. High blood pressure detected at the doctor’s office appeared in 79.2 percent of patients whose masked hypertension was identified with the device, compared to only 42.2 percent of people without masked hypertension. In other words, a device like this may be able to catch high blood pressure that otherwise goes undetected.

“Our study found that African-Americans with any masked hypertension had twice the risk of developing clinic hypertension when compared to those who had both normal clinic and normal out-of-office blood pressure,” said Dr. Marwah Abdalla, a cardiologist at Columbia University Medical Center and lead author of the study, in a press release. “The risk was also high among those with masked nighttime hypertension — a condition where blood pressure is only elevated at night or while asleep. We also found that even among those with normal blood pressure for example, (less than 120 mm Hg/80 mm Hg) during a clinic visit, individuals with masked hypertension had a high risk of developing clinic hypertension.”

The authors hope that their study will provide more impetus for the use of wearable blood pressure monitoring devices as a preventive measure for undetected hypertension.

Source: Abdalla M, Booth J, Seals S, Spruill T, Viera A, Diaz K, et al. Masked Hypertension and Incident Clinic Hypertension Among Blacks in the Jackson Heart Study. Hypertension , 2016.