When your blood pressure number fools you — or your doctor

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Some people are told they have high blood pressure during a hospital visit, only to find their levels are perfectly normal at home. Others may believe they’re healthy, unaware that they’re actually living with hypertension. These two conditions — known as white coat hypertension and masked hypertension — often go unnoticed but can carry serious health consequences if misunderstood.

White coat hypertension refers to cases where a person’s blood pressure rises in clinical settings but remains normal in daily life. In contrast, masked hypertension describes those who have consistently high blood pressure outside the hospital but show normal levels during check-ups. Both conditions are more common than many realize, with an estimated prevalence of around 10 percent in the general population — rising to 20–30 percent among high-risk groups such as those with diabetes.

Experts say psychological factors play a major role. “For white coat hypertension, it’s often the anxiety — worrying about the diagnosis, or the idea that something might be wrong — that causes the spike,” said Dr. Oh Min-seok, a cardiologist at Bundang Jesaeng Hospital. This anxiety activates the autonomic nervous system, releasing stress hormones that temporarily raise blood pressure. Other factors, like drinking coffee or smoking right before a check-up, can also produce misleadingly high readings.

Masked hypertension presents the opposite challenge. According to Oh, many individuals with this condition mistakenly assume their lowest blood pressure reading is their “true” one. Blood pressure naturally fluctuates — typically higher in the morning and lower at night — but those with masked hypertension may focus only on the low readings. The term “masked” reflects the misleading appearance of normalcy.

Unlike white coat hypertension, masked hypertension poses a real threat. As an actual form of high blood pressure, it leaves individuals exposed to the full range of cardiovascular risks: heart failure, arrhythmia, myocardial infarction and stroke, as well as vascular dementia and cognitive decline. According to data from the Health Insurance Review and Assessment Service on Monday, the number of hypertension patients in Korea rose from 6.31 million in 2019 to 7.27 million in 2022.

To differentiate between true hypertension and its psychological variants, home monitoring is essential. Experts recommend measuring blood pressure at rest, after urinating and at least 30 minutes after exercise or caffeine intake. It’s important to focus on the average reading, not the lowest, and to use the higher value if readings differ between arms.

Another key point is that home and hospital blood pressure thresholds differ. At the hospital, hypertension is diagnosed when systolic pressure is 140 mmHg or higher and diastolic is 90 mmHg or higher. At home, the bar is lower: systolic of 135 mmHg or more and diastolic of 85 mmHg or more is considered hypertensive.

“Because both masked and white coat hypertension are rooted in psychological stress, mental relaxation is crucial,” Oh said. “In some cases, those with white coat hypertension may even require psychiatric counseling or treatment.”

This article from the Hankook Ilbo, the sister publication of The Korea Times, is translated by a generative AI system and edited by The Korea Times.