Hypertension affects more than 1.3 billion adults worldwide. Yet, its often silent nature means it may go undetected for years. In-office blood pressure measurements once or twice a year may also miss it. 

Could the Apple Watch hypertension notification feature, recently cleared by the US FDA, help address this diagnosis gap? 

“This kind of technology and advancement are, to me, exciting. Taking biometric monitoring outside of the clinic and into the home gives an opportunity for us to — almost literally — take our health into our own hands,” Ankur Shah, MD, Division of Kidney Disease and Hypertension, Warren Alpert Medical School of Brown University, Providence, Rhode Island, told Medscape Medical News.

“Particularly in hypertension, I care more about what your blood pressure is the 364 days you are at home than the 1 day you are in the office, particularly as it can be falsely high or low in the office. The falsely low, which is referred to as masked hypertension, are cases that a wearable can detect that we currently aren't,” Shah said. 

What It Does and Doesn’t Do 

The Apple Watch hypertension feature — available on Apple Watch series 9 or later and Apple Watch Ultra 2 or later (excluding Apple Watch SE) — is intended for use in nonpregnant adults aged 22 years or older who have not been previously diagnosed with hypertension. 

It passively analyzes 60-second segments of photoplethysmography (PPG) collected during waking hours about every 2 hours throughout nonoverlapping 30-day evaluation windows. 

It does not measure blood pressure directly or give the user a blood pressure reading.

Instead, it notifies users if optical heart sensor data show signs of hypertension after 30 days. If signs of hypertension are detected, users are notified of “possible hypertension” — hopefully to prompt confirmatory testing.

“The Apple Watch possible hypertension should not be used in place of standard blood pressure measurements by sphygmomanometer,” Pradeep Natarajan, MD, MMSc, director of preventive cardiology, Mass General Hospital, and associate professor of medicine, Harvard Medical School, Boston, told Medscape Medical News.

“However, its broad use in the population has the possibility to uncover many new cases of hypertension, the most common cardiovascular disease risk factor in the world,” Natarajan said. 

How Was It Developed? 

Apple developed the feature’s algorithm using machine learning techniques and a large dataset from a diverse group of adults. To check how well it works in the real world, Apple ran a separate, pivotal study with more than 2000 adults without a prior hypertension diagnosis. Participants wore the Apple Watch at least 12 hours a day for 30 days and took home blood-pressure readings twice daily with an OMRON Evolv blood pressure cuff. 

Overall sensitivity was 41.2% (95% CI, 37.2-45.3) and specificity was 92.3% (95% CI, 90.6-93.7). Sensitivity was higher for those with stage 2 hypertension (53.7%; 95% CI, 47.7-59.7). 

Specificity among people with normal blood pressure was 95.3% (95% CI, 93.7-96.5), indicating that a significant portion of people who did not receive a possible hypertension alert actually had elevated blood pressure.

“While tests for screening prioritize sensitivity, to ensure cases are not missed, this feature prioritizes specificity. This means that Apple wants to minimize false positives, which generally makes sense for a nonmedical commercial device,” Natarajan told Medscape Medical News. 

He noted that hypertension is far more common than atrial fibrillation, “suggesting that the likelihood the alert yields a true positive, or the positive predictive value, is higher for hypertension than atrial fibrillation.”

However, he cautioned that by prioritizing specificity, sensitivity suffers and many individuals with true hypertension will not get an alert. “So the absence of an alert is insufficient to rule out hypertension,” Natarajan said. 

Positive Alert: Now What? 

Apple support advises individuals who get a “possible hypertension” alert to discuss the notification with their doctor at their next appointment. 

The feature also prompts users to set up a blood pressure log and use a third-party blood pressure cuff to measure and track blood pressure for 7 days.

As a clinician, Shah said he would take an alert seriously and evaluate the patient further, “but I would not take the absence of alerts to mean the absence of hypertension, and in someone who I am making a new diagnosis of hypertension, I wouldn't be less apt to treat based on a lack of Apple Watch alerts.”

What About Other Wearables?

The Samsung Galaxy Watch3 and Galaxy Watch Active2 offer on-demand blood pressure measurement via the Samsung Health Monitor app, but it requires regular cuff calibration and availability varies by regulatory market. It’s not available in the US due to lack of FDA clearance. 

The OMRON HeartGuide is an FDA-cleared wristwatch that monitors blood pressure. It uses oscillometric technology to take readings and was launched in the US in January 2019.

Google is actively testing a hypertension screening feature for the Pixel Watch, which involves sensor data and user input, and may be integrated into Fitbit devices in the future.

Natarajan and Shah had no disclosures.