As many as 30 to 40 percent of adults told they have high blood pressure on the strength of a clinic reading actually have normal pressure when it is measured elsewhere.
The phenomenon has a name, white coat hypertension, and a new US guideline says the office cuff can no longer be trusted on its own.
The 2025 hypertension guideline from the American Heart Association, the American College of Cardiology and 11 other medical societies was published on August 14, 2025 in the Journal of the American College of Cardiology.
It is the first major update since 2017, and it moves home blood pressure monitoring from an optional add-on to a central part of both diagnosis and long-term management.
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The shift matters because two different kinds of misclassification pull in opposite directions. Some adults are treated for pressure that only rises inside a clinic.
Others walk out with a clean bill of health when their pressure is quietly elevated at home. The guideline pushes clinicians to sort out which is which before writing, or withholding, a prescription.
What white coat hypertension actually is
White coat hypertension describes a reading that is high in a medical setting but normal outside it.
Under the 2025 US thresholds, that means an office reading at or above 130/80 mm Hg paired with daytime out-of-office readings below 130/80 mm Hg.
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A narrative review of primary care evidence reported that 30 to 40 percent of patients diagnosed on office readings alone had normal ambulatory blood pressure when measured over 24 hours.
The clinical stakes are not trivial. People with white coat hypertension face a higher risk of progressing to sustained high blood pressure over the following decade, but the immediate cardiovascular risk sits somewhere between healthy pressure and true hypertension.
The 2025 guideline calls it reasonable to rule out white coat hypertension using out-of-office monitoring before making a diagnosis in adults with office readings between 130/80 and 160/100 mm Hg.
The opposite problem is easy to miss
Masked hypertension is the mirror image: normal in the clinic, high at home.
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Recent US estimates suggest roughly one in six American adults may fall into this category, and the American Medical Association has described it as a blind spot in routine care.
The condition carries about a 1.7 times higher risk of cardiovascular events compared with people whose pressure is normal in both settings.
That is why the new guideline warns against under-treating people whose office numbers look reassuring.
If home readings run higher than expected, or symptoms and risk factors do not match the clinic number, out-of-office monitoring is the way to catch it.
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Existing Welltica reporting has covered other overlooked drivers of hypertension that can compound the problem.
How to measure at home so the numbers count
Home readings are only useful if the technique is right. The American Heart Association's home monitoring guidance says to sit quietly for five minutes first, with both feet flat on the floor and back supported, then rest the arm on a flat surface at heart level.
Skip caffeine, exercise and tobacco for 30 minutes beforehand, and empty the bladder. Take two readings a minute apart and record the average.
The device itself matters. The AHA recommends an upper-arm cuff that has been independently validated for accuracy.
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The 2025 guideline is explicit that cuffless blood pressure devices are not recommended for diagnosing or treating high blood pressure, because they lack sufficient external validation.
Cuff position is another common trap, as previous Welltica reporting on how arm position skews readings has explained.
When to ask about ambulatory monitoring
If home and clinic readings disagree, or the picture is still unclear, the guideline points to 24-hour ambulatory blood pressure monitoring.
That involves wearing a device that takes readings automatically through a full day and night, including during sleep.
It is the reference standard for confirming both white coat and masked hypertension and for deciding whether medication is really warranted.
Validated home monitors can be found on ValidateBP.org, a registry run in partnership with the AHA and the AMA that lists devices tested for accuracy against reference standards.
This article is made and published by Mie Hermansen, who may have used AI in the preparation.