White-Coat & Masked Hypertension: ABPM, HBPM, Risk and Evidence

Table of contents

• Evidence summary
• What white-coat and masked hypertension are
• Symptoms and red flags
• Causes and risk factors
• How it is diagnosed: ABPM and HBPM
• Cardiovascular risk: what the cohorts show
• SPRINT-style measurement differences
• Device accuracy
• Treatments: what works and what does not
• Medicines
• Supplements and lifestyle claims
• Risks and limits
• Who to see
• Follow the money: who makes the monitors and who funded the evidence
• Related research
• Frequently asked questions
• Sources and funding notes

Evidence summary

Independent evidence and credibility scorecard

Independence tiers: 1 = regulator, national guideline body or government task force; 2 = academic, charity or government-funded research with no declared manufacturer funding for the work (any declared ties are noted); 3 = authors or organisations with documented ties to monitor makers or to validation-for-fee businesses; 4 = manufacturer-run or manufacturer-authored. Credibility runs from A (highest) to D. For monitor accuracy, we treat the monitor maker as the nearest equivalent of a drug manufacturer. Our sources cluster in the UK, US, Spain, Italy and Japan, and the authors overlap heavily: the same hypertension-society network (for example Williams, Stergiou, Asayama, Franklin, Mancia) appears across several papers and guidelines.

What white-coat and masked hypertension are

Hypertension is persistently raised blood pressure. NICE confirms it when the clinic reading is 140/90 mmHg or higher and the ABPM daytime average or home average is 135/85 mmHg or higher (NG136, 1.2.8). Two mismatches follow.

• White-coat hypertension: clinic pressure is high (140/90 or above) but ambulatory or home pressure is normal. The European guideline summary explains this as an "alerting reaction" in the medical setting (Grassi 2025). In treated patients the same gap is called the "white-coat effect" (Cohen 2019).
• Masked hypertension: clinic pressure is under 140/90 but daytime ambulatory or home pressure is higher (NICE terms). In people already on treatment it is called masked uncontrolled hypertension (Ghazi 2020).

How common are they? Estimates depend heavily on the method and cut-offs. White-coat hypertension is reported in about 20% to 25% of people with mild-to-moderate raised clinic pressure, and anywhere from 15% to 45% depending on definitions. In the PAMELA population study near Milan, 9% to 12% of 1,637 untreated people had it. Masked hypertension is put at 10% to 25% (Grassi 2025). A 2024 meta-analysis of 26 studies pooled a prevalence of 18% (95% CI 15% to 21%) (Zhu et al.). These are not fixed labels: in the Spanish registry, about 30% of people with masked hypertension had moved to sustained hypertension by a repeat recording roughly three months later, which the guideline summary takes to mean the pattern is unstable for many people (Grassi 2025).

Symptoms and red flags

High blood pressure does not usually cause symptoms. Rarely it can cause headaches, blurred vision or chest pain, and the NHS says the only way to find out is to have it measured (NHS). That is the whole problem with masked hypertension: there is nothing to feel and the clinic reading looks fine. White-coat hypertension also causes no symptoms of its own.

The red flags that matter are not about the phenotype but about severe readings. NICE asks for same-day specialist assessment when clinic pressure is 180/120 mmHg or higher with retinal haemorrhage, swelling of the optic nerve, new confusion, chest pain, signs of heart failure or acute kidney injury. It also asks for same-day assessment when a phaeochromocytoma is suspected, for example with labile pressure, headache, palpitations, pallor, abdominal pain or sweating (NG136, 1.5.2 and 1.5.3). For a severely high reading with no such features, NICE advises looking for organ damage promptly and confirming with a repeat clinic reading within 7 days or ABPM, rather than assuming a white-coat effect (NG136, 1.5.1).

Causes and risk factors

White-coat hypertension. The gap between clinic and ambulatory pressure grows with age: in the pooled IDACO cohorts the systolic white-coat effect rose by 3.8 mmHg (95% CI 3.1 to 4.6) for every 10 years of age, and size of the effect was linked to ageing rather than to cardiovascular risk (Franklin 2016). People with white-coat hypertension in the PAMELA study had more heart, kidney or blood-vessel changes (about 30% to 35%) than people with normal readings everywhere (about 10%), and a higher long-term chance of developing sustained hypertension (Grassi 2025). Other studies found organ-damage profiles similar to normal pressure (same review).

Masked hypertension. Reported associations are male sex, older age, high-normal clinic pressure, low physical activity, obesity, smoking, and regular alcohol drinking. Sympathetic (adrenaline-type) nervous system activation is proposed as a driver. The same review lists diabetes, chronic kidney disease, obesity and sleep apnoea as settings where masked hypertension is studied (Grassi 2025). General risk factors for hypertension include age, family history, Black African, Black Caribbean or South Asian background, a high-salt diet, excess weight, smoking and alcohol (NHS). Secondary causes are a separate question (see our secondary hypertension guide).

How it is diagnosed: ABPM and HBPM

NICE sets out a stepwise approach (NG136, section 1.2):

• Measure in both arms. If the arms differ by more than 15 mmHg, repeat, and use the higher arm if the gap persists.
• If the clinic reading is 140/90 or higher, take a second reading, and a third if they differ substantially. Record the lower of the last two.
• If clinic pressure is between 140/90 and 180/120, offer ABPM. If ABPM is unsuitable or not tolerated, offer HBPM.
• For ABPM, take at least two readings an hour during usual waking hours and use the average of at least 14 daytime readings.
• For HBPM, take two readings at least a minute apart, seated, twice a day (morning and evening), for at least 4 days and ideally 7. Discard day one and average the rest.
• Diagnose hypertension when the clinic reading is 140/90 or higher and the ABPM daytime or HBPM average is 135/85 or higher. A raised clinic reading with a normal out-of-office average is, by definition, white-coat hypertension.
• If hypertension is not diagnosed, re-measure clinic pressure at least every 5 years, and more often if the clinic reading is under 140/90 but still raised.

One gap stands out. These steps start with a raised clinic reading. NICE defines masked hypertension but, in the recommendations we read, offers ABPM or HBPM for masked hypertension only to people who already have a hypertension diagnosis (NG136, 1.4.18). A person with a clinic reading of 128/82 and a home average of 140/90 is unlikely to be tested. The US Task Force likewise recommends screening with office readings, then outside-clinic confirmation before treatment (USPSTF 2021). The 2023 European guideline, as described by its editors, encourages ABPM, HBPM or both for diagnosing both phenotypes (Whelton et al. 2023). We could not open the full European or the 2025 US guideline text, so we do not report their exact class-of-recommendation wording.

Thresholds differ by method: for people with hypertension, NICE notes that the ABPM and HBPM equivalents are about 5 mmHg lower than clinic values (NG136, 1.4.18). For how to measure at home, see our home blood pressure monitoring guide.

Cardiovascular risk: what the cohorts show

Masked hypertension

Four separate lines of evidence point the same way, which matters because they come from different countries and designs. In Ohasama (Japan, 1,332 adults aged 40 or over, about 10 years), masked hypertension carried a relative hazard of 2.13 (1.38 to 3.29) for cardiovascular death or stroke, about the same as sustained hypertension at 2.26 (1.49 to 3.41) (Ohkubo 2005). In the International Database of Home Blood Pressure (6,458 people from five populations, median 8.3 years), masked hypertension measured at home gave an adjusted HR of 1.55 (1.12 to 2.14) in untreated people and 1.76 (1.23 to 2.53) in treated people against controlled patients, meaning people on treatment whose home readings stay high are also at risk (Stergiou 2014). The corrected Spanish registry gave 1.24 for all-cause death (Staplin 2023), and the 2024 meta-analysis RR 1.57 (1.45 to 1.69) for new cardiovascular disease (Zhu 2024).

In plain English: people whose pressure looks normal in the clinic but is raised outside it have roughly one and a quarter to twice the risk of the people whose pressure is normal everywhere, in studies that did not randomise anyone. These are associations, not proof that lowering the pressure removes the risk.

White-coat hypertension

The picture is less clear. Untreated white-coat hypertension carried higher risk in the 27-study meta-analysis (cardiovascular events HR 1.36, cardiovascular death HR 2.09), with the effect weaker, at 1.26 (1.00 to 1.54), once studies counting stroke were considered, and no raised risk for the treated white-coat effect (events HR 1.12, 0.91 to 1.39) (Cohen 2019). In the IDACO cohorts, the excess appeared only in 159 high-risk people (HR 2.06, 1.10 to 3.84), driven by those aged 60 or over (HR 2.19, 1.09 to 4.37), while older low-risk people showed no excess (HR 0.88, 0.51 to 1.53) (Franklin 2016). In the home-measured database, risk was raised in untreated people (HR 1.42, 1.06 to 1.91) but not in treated ones (1.16, 0.79 to 1.72), which the authors read as effective treatment already given on the basis of the high clinic reading (Stergiou 2014). A 29-year follow-up of 1,423 people from PAMELA with no organ damage found cardiovascular death HR 2.0 (1.1 to 3.6) versus normal pressure (Mancia 2022). The corrected Spanish registry found no excess (Staplin 2023).

Taken together, the honest summary is "intermediate and uncertain": similar to normal in many younger or lower-risk groups, higher in older or higher-risk groups, and possibly a precursor of sustained hypertension over decades.

SPRINT-style measurement differences

The SPRINT trial tested a systolic target below 120 mmHg against below 140 mmHg and became a reference point for lower targets. Two features matter for this topic.

How pressure was taken. Commentary often says SPRINT used "unattended" readings, taken with the patient alone. The trial's own investigators later wrote that the protocol did not address attendance. A survey at close-out found that 4,082 participants were at 38 sites that always measured alone, 2,247 at 25 sites that never did, 1,746 at 19 sites that left people alone only during the rest period, and 570 at 6 sites alone only during readings. Blood pressures and the benefit of intensive treatment were similar in the always-alone group (HR 0.62, 0.51 to 0.76) and the never-alone group (HR 0.64, 0.46 to 0.91). The survey was run after the trial ended (Johnson 2018). The practical message is that a research-style reading, with a rested patient, a validated automatic device, the right cuff and an average of several readings, will differ from a quick reading in a busy clinic, which may contribute to the clinic-versus-home gap.

Office and ambulatory pressure still diverged. In 897 SPRINT participants who had ambulatory monitoring 27 months in, white-coat effect and masked uncontrolled hypertension were present in 9% and 34% respectively, in both arms. Among those with controlled office pressure (below 120/80 in the intensive arm), masked uncontrolled hypertension was present in 62% of the intensive group and 56% of the standard group (Ghazi 2020). The thresholds used differ by arm (intensive: daytime 120/80 or higher; standard: 135/85 or higher), so these percentages describe each arm's own targets, not a like-for-like comparison. They do show that even with careful research measurement, office readings at target did not guarantee out-of-office control. This is one reason NICE and others do not equate a research target with a routine clinic reading. For NICE's clinic targets, see NG136, 1.4.20, and for the wider picture our hypertension guide.

Device accuracy

Diagnosis of both phenotypes depends on the home or ambulatory cuff being right. A 2020 position statement from members of the Lancet Commission on Hypertension said there are over 3,000 commercial devices, many without accuracy data from accepted protocols, and that weak regulation lets devices be cleared for sale without formal validation. It argued this causes inappropriate diagnosis and treatment, and called for mandatory independent validation to the ISO standard and for public lists of accurate devices (Sharman et al. 2020).

The lists exist but differ in how they work. A 2023 guide compared them (Picone et al.):

• US Validated Device Listing (validatebp.org): manufacturers apply; an independent expert committee reviews their documents and decides; listing is not dependent on published papers.
• STRIDE BP: two reviewers check each published validation study, then two members of the advisory board review it before listing. It is endorsed by the European Society of Hypertension, the International Society of Hypertension and the World Hypertension League.
• British and Irish Hypertension Society (BIHS): a working party reviews published validation studies. NICE points to this list.
• Medaval: described as the only list to include non-validated devices, and as a private, for-profit organisation not affiliated with scientific societies.

The quality of the underlying papers matters. In a STRIDE BP review of 419 published validations, 12% were rejected by the publishing journals but 31% by STRIDE BP; of 79 validations approved in journals but rejected by STRIDE BP, 91% were rejected for poor study execution, analysis or reporting, not for device inaccuracy (STRIDE BP 2019). The STRIDE website now says it has approved 551 monitors and recommends as preferred 294 of the over 5,000 electronic monitors on the market (STRIDE BP). Automated devices may also read inaccurately with an irregular pulse such as atrial fibrillation; NICE advises feeling the pulse first and measuring manually if it is irregular, and standardising the setting and cuff size (NG136, 1.1.2 to 1.1.4). Cuffless and wearable devices are a separate and less settled question: the Lancet Commission group noted that new technologies such as cuffless sensors have no scientific consensus on accuracy standards (Sharman 2020).

Treatments: what works and what does not

The treatment gap is the main finding of this article. Everyone in the cohort studies was treated, or not, by ordinary clinical judgement. The two groups could differ in many ways that also affect outcomes. That is why the guideline authors recommend lifestyle advice and monitoring, and reserve drugs for people with other markers of risk.

Medicines

For people confirmed to have hypertension, NICE recommends drug treatment alongside lifestyle advice for persistent stage 2 hypertension at any age, and a discussion about starting treatment for people under 80 with persistent stage 1 hypertension who have organ damage, established cardiovascular disease, kidney disease, diabetes or a 10-year cardiovascular risk of 10% or more. It asks clinicians to discuss individual risk and preferences, including no treatment (NG136, 1.4.9 to 1.4.11). Stage 1 means a clinic reading of 140/90 to 159/99 mmHg with a confirming ABPM or HBPM average of 135/85 to 149/94 mmHg (NG136 terms). A person with a raised clinic reading and a normal out-of-office average does not meet the diagnostic threshold, so these rules do not automatically apply. Risk calculators such as those described in our cardiovascular risk calculators guide help decide who has "high risk", though NICE tells clinicians to use clinic readings to calculate it (NG136, 1.3.2).

We did not find a trial of any specific drug class in white-coat or masked hypertension alone, so we cannot say which medicines suit these groups. For what the main classes do and their side effects, see our blood pressure medicines guide. If a person is already on treatment and monitoring shows a gap, the decision belongs to their prescriber.

Supplements and lifestyle claims

Risks and limits

• Missed masked hypertension. If a clinic reading is the only test, people with masked hypertension are unlikely to be found, yet they carry higher risk (Ohkubo 2005).
• Unstable labels. A single recording may not predict the next one. Most studies classified people from one ambulatory or home session (Grassi 2025).
• Inaccurate or wrongly used devices. Unvalidated monitors, the wrong cuff size, a relaxed-setting failure or an irregular pulse can all produce misleading numbers (Sharman 2020; NG136, 1.1).
• Not suitable for everyone. NICE accepts that some people cannot tolerate ABPM and offers HBPM instead (NG136, 1.2.4). Orthostatic (standing) drops are assessed separately; see our orthostatic hypotension guide.
• Stopping or changing medicine on home readings alone. NICE says people who self-monitor need training and information on what to do if readings are off target (NG136, 1.4.19).
• Evidence limits. Nearly all the risk data are observational, definitions of "normal" out-of-office pressure vary, and some of the largest datasets come from one hypertension-society network (Ohasama, IDACO and IDHOCO share several authors).

Who to see

A GP, practice nurse or pharmacist can check blood pressure; the NHS says to get a check at a pharmacy or GP surgery if you are 40 or over and have not had one for more than 5 years, and that some pharmacies may charge (NHS). In the UK a clinician can arrange ABPM or HBPM when the clinic reading is 140/90 or above. In the US, the Task Force recommends outside-clinic confirmation before treatment starts (USPSTF 2021). People with diabetes, kidney disease or existing heart disease, older adults and people whose readings differ widely between settings should discuss monitoring with their clinician, since these are the groups in which the risk data are strongest. A cardiologist or hypertension specialist is usually involved when readings are very high, treatment is hard to control, or a secondary cause is suspected (see resistant hypertension and hypertensive emergency).

Follow the money: who makes the monitors and who funded the evidence

Who profits from monitoring

Blood pressure monitors are a consumer-device market with many brands. We did not find a citable market-size figure or a market-share ranking, so we do not give one. Omron Healthcare is one manufacturer whose monitors appear in this evidence: the HEM-1040 paper identifies Omron Healthcare Co., Ltd., of Kyoto, Japan, as its maker (Takahashi 2020), and the company's US page describes OMRON Healthcare, Inc. (Omron). We did not trace the group's ownership or finances beyond those names. Our inference, not a sourced finding: more people told to monitor at home means more monitors sold, and a place on a "validated" list is a selling point.

The validation lists and their money

• US Validated Device Listing: convened by the American Medical Association and run through an independent review committee managed by the National Opinion Research Center at the University of Chicago, according to Omron's own page, which also says Omron was one of the first three manufacturers on the list (Omron). Manufacturers apply to be listed (Picone 2023). Two committee co-chairs are authors of the Picone guide, and one reports funding or salary support from Resolve to Save Lives, which the paper says is funded by Bloomberg Philanthropies, the Bill and Melinda Gates Foundation and Gates Philanthropy. We could not confirm who pays for the list itself.
• STRIDE BP: a non-profit founded in 2019 inside the Hypertension Centre STRIDE-7 at the University of Athens, Greece, in affiliation with the European Society of Hypertension, the International Society of Hypertension and the World Hypertension League (STRIDE BP). Its affiliated sponsors page names the Chinese Hypertension League and the French Society of Hypertension (sponsors). Its chair declares that he has conducted validation studies and advised manufacturers (Picone 2023). We found no statement of the list's annual budget or any corporate donors.
• BIHS list: reviewed by a working party. Its chair, who is an author of the Picone guide, reports having received monitors from Omron for research and working with Omron on a telemonitoring system, with fees paid to his institution (Picone 2023). We did not find who funds the list.
• Medaval: a private firm that, per the same declarations, relies on fees for validation, equivalence and accreditation services to manufacturers.
• Other Omron links in the evidence: a co-author of the Picone guide reports research support from Omron Healthcare. In the Lancet registry paper, one author reports investigator-led grant support from Omron for unrelated research (Staplin 2023). In the HEM-1040 validation, the one declared author is an Omron employee, the study had company approval, and measurements were made in the company's room by its staff (Takahashi 2020). None of this shows any result is wrong. It does show the monitoring ecosystem is not free of manufacturer money.

Who funded the outcome evidence

The risk studies are mostly publicly or charitably funded, or carry no named funder: the US National Institutes of Health (Cohen; SPRINT), the UK Medical Research Council and other public bodies, plus the Spanish Society of Hypertension and Lacer Laboratories, a Spanish drug company (Staplin), Chinese hospital research grants (Zhu), and unnamed non-US government support (Ohasama, IDACO, IDHOCO). SPRINT authors declare grants or consulting from several drug makers, including Eli Lilly, AstraZeneca, Takeda and Novartis (Johnson 2018). The treatment gap is a funding story too: a trial of drugs in white-coat hypertension would be expensive, and generic blood pressure drugs offer little commercial return. That is our inference; we found no source stating it.

Documented integrity events

The one we can document is the January 2020 retraction of the 2018 NEJM registry paper, described above. A signatory of the retraction letter from University College London is also an author of the Lancet re-analysis, whose declaration records an Omron investigator-led grant to a UCL author for separate research (Staplin 2023; retraction). We found no regulatory action, recall or lawsuit involving Omron, but our search for such events was cut short by a search limit during this review, so absence in this article is not a clean bill of health.

Related research

For wider, evidence-graded context, see these Pure City Research guides:

• Home blood pressure monitoring
• Hypertension
• Blood pressure medicines
• High blood pressure: prevention and management
• Blood pressure supplements
• Resistant hypertension
• Secondary hypertension
• Hypertensive emergency
• Cardiovascular risk calculators
• Orthostatic hypotension
• Stress and physical health

Frequently asked questions

Sources and funding notes

What we could not verify: how much the Spanish Society of Hypertension and Lacer Laboratories contributed to the Spanish registry work, or whether they had any role in its analysis (the Lancet record names them only in the funding line); the full text of the 2023 European Society of Hypertension guideline and the 2025 US guideline (the publisher sites blocked automated access), so we rely on their authors' and editors' summaries. Funding statements were not visible in the records we opened for Franklin 2016, Ohkubo 2005, Stergiou 2014, Mancia 2022 or the Task Force statement; PubMed tags the first three as non-US government supported without naming funders. We found no funding line for NICE on the pages we opened. We could not open the tctmd news reports about the retraction and re-analysis because the site blocked access, so the cause of the 2018 error is described only in the authors' words. We could not find or open the BIHS and US Validated Device Listing funding statements, and the validatebp.org site blocked access. We did not trace Omron's ownership, market share or any recall or regulatory history because a search limit stopped our searching. The Banegas, Cohen, Franklin and Mancia hazard ratios compare people with different definitions of "normal" out-of-office pressure, so cross-study comparison is approximate. Where a source says "Franklin meta-analysis", note that the 2016 JACC paper is a matched analysis of pooled cohort data, not a meta-analysis of published trials.

1. NICE NG136. Hypertension in adults: diagnosis and management — UK guideline; public body, funding line not seen.
2. NICE charter — roles and mandatory NHS funding of recommended treatments.
3. US Preventive Services Task Force. Screening for hypertension in adults (JAMA 2021) — US task force; supported by AHRQ.
4. About the USPSTF — role of AHRQ.
5. Staplin et al. Lancet 2023 — registry re-analysis; funders include the Spanish Society of Hypertension, Lacer Laboratories (a drug company), MRC, NIHR and others; one author with Omron grant for separate research.
6. Banegas et al. NEJM 2018 — retracted; Spanish Society of Hypertension and others.
7. Retraction notice, NEJM 2020 and letter text — authors' statement.
8. Cohen et al. Ann Intern Med 2019 — meta-analysis; US NIH (NHLBI).
9. Franklin et al. JACC 2016 — IDACO analysis; non-US government support, funder not named.
10. Ohkubo et al. JACC 2005 (Ohasama) — Japanese cohort; non-US government support, funder not named.
11. Stergiou et al. Hypertension 2014 (IDHOCO) — home-BP database; non-US government support, funder not named.
12. Mancia et al. Hypertension 2022 (PAMELA) — Italian cohort; funding not seen.
13. Zhu et al. J Evid Based Med 2024 — meta-analysis; two Chinese research grants.
14. Grassi et al. 2025, phenotypes in the 2023 ESH guideline — review; no external funding, no conflicts declared.
15. Whelton et al. Hypertension 2023, editors' commentary on the 2023 ESH guidelines — independent commentary; authors declare various industry grants including Omron and Novartis for one author.
16. 2023 ESH guidelines, J Hypertens — guideline; full text not opened.
17. Johnson et al. Hypertension 2018, SPRINT blood pressure measurement — US NIH; several pharmaceutical grants declared.
18. Ghazi et al. Hypertension 2020, SPRINT ABPM ancillary study — US NIH institutes.
19. Sharman et al. J Hypertens 2020, Lancet Commission group statement — UK Department of Health (NIHR) grant tag.
20. STRIDE BP, J Clin Hypertens 2019 and J Hypertens 2020 — list reviewers' own papers.
21. STRIDE BP, about us, affiliated sponsors and home page — non-profit; affiliated societies.
22. Picone et al. J Hum Hypertens 2023, how to find validated devices — authors with Omron and validation-firm ties declared.
23. Takahashi et al. Vasc Health Risk Manag 2020, Omron HEM-1040 validation — manufacturer employee; tested at manufacturer's facility.
24. Omron Healthcare, clinical validation — manufacturer marketing page.
25. NHS: high blood pressure — UK public health service; patient information.

Educational research reviewed 6 October 2026. This article is not medical advice; talk to a qualified clinician or pharmacist before starting, stopping or combining treatments.