Wearing a 24-hour monitoring device may help identify African-Americans who have masked or undetected high blood pressure outside the doctor’s office, according to new research in the American Heart Association journal Hypertension.

Masked hypertension is normal blood pressure in the doctor’s office, but high readings outside the office that are easy to miss during the day or night. It’s the reverse of white coat hypertension, which is higher blood pressure readings at the doctor’s office.

Blood pressure naturally fluctuates throughout the day. To discover who might have masked hypertension among a high-risk population, researchers used ambulatory blood pressure monitoring, in which patients wear a compact cuff around the arm connected to a device worn at the hip.

The advantage to ambulatory blood pressure monitoring is that it provides readings of blood pressure over 24 hours while doing normal daily activities. On the other hand, home monitoring requires a person to check his or her blood pressure at certain times, and can’t be performed while the patient sleeps.

The study included 317 African-Americans in the Jackson Heart Study, an ongoing, population-based study in Jackson, Mississippi, that examines factors associated with and occurrence of heart disease among African-Americans.

When enrolled in the new study, participants didn’t have high blood pressure and weren’t on high blood pressure medication. They wore ambulatory blood pressure monitors at the first clinic visit and their readings were compared with two taken at subsequent visits. Participants were followed for an average 8.1 years and 187 developed high blood pressure.

Researchers found:

  • Clinic high blood pressure developed in 79.2 percent of participants with masked hypertension compared to only 42.2 percent of participants without masked hypertension.
  • Clinic high blood pressure developed more in participants who had masked daytime hypertension, masked nighttime hypertension or masked 24-hour hypertension.

“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 Marwah Abdalla, M.D., M.P.H., lead study author and cardiologist at Columbia University Medical Center in New York.