To be (IIb), or not to be (IIb) – That is the current status of cuffless blood pressure monitoring device

Abstract

Cuffless blood pressure (BP) monitoring devices have attracted extraordinary scientific and commercial attention, yet their clinical status remains deeply contested. Major international guidelines from the American Heart Association/American College of Cardiology (2025), the European Society of Cardiology (2024), and the European Society of Hypertension (ESH, 2023) uniformly assign a Class III recommendation (not recommended for diagnostic use) to cuffless devices due to insufficient validation and calibration drift. However, the Korean Society of Hypertension has recently updated its guidelines to include cuffless BP monitors as a Class IIb recommendation for out-of-office BP measurement. This review explores the rationale behind this divergence, largely based on the acclumulating validation of a domestic ring-type cuffless device, CART BP (Sky Labs), currently the world’s only nationally insured cuffless monitor. We analyze the historical landscape of international validation, detail the sequential fulfillment of ESH criteria, and delineate future research imperatives—emphasizing calibration practicality, transient BP changes, and cardiovascular outcome validation—to pave the way for universal clinical adoption.

Graphical Abstract

WHERE DO WE COME FROM?: THE ORIGINS AND EVOLUTION OF CUFFLESS BLOOD PRESSURE (BP) MONITORING

The unmet need that drove a revolution

Hypertension remains the leading modifiable risk factor for cardiovascular death, affecting 1.3 billion people globally yet remaining inadequately controlled in nearly half of treated patients [1,2,3]. The cornerstone of its management is accurate BP measurement, but BP’s high susceptibility to behavioral and environmental factors necessitates repeated measurements to gauge true cardiovascular risk [4,5]. Furthermore, diurnal variations such as blunted nocturnal dipping strongly predict cardiovascular events independent of average BP levels [6,7,8,9,10].

Office BP measurement is susceptible to the alerting reaction and may therefore misrepresent an individual’s usual BP. White-coat hypertension affects 15–30% of patients with apparent hypertension, while masked hypertension affects 10–20% of apparently normotensive individuals, carrying risks equivalent to sustained hypertension [11]. Thus, recent major international guidelines strongly recommend out-of-office BP measurement [11].

While ambulatory blood pressure monitoring (ABPM) remains the 24-hour gold standard, current cuff-based systems cause discomfort, disrupt sleep, potentially limiting their tolerability and repeated use [12,13]. Cuffless devices—particularly those utilizing photoplethysmography (PPG) and wearable platforms—offer continuous, passive monitoring that improves patient comfort and allows repeated nocturnal assessments without disturbing sleep, offering new clinical opportunities to optimize management [14,15,16,17].

The technologies: principles and promise

Cuffless monitoring technologies primarily use pulsatile hemodynamic signals as surrogates for arterial pressure. The dominant method couples PPG—optical sensing of blood volume changes—with machine learning-based pulse wave analysis (PWA). Alternative methods such as pulse transit time (PTT) use the inverse relationship between arterial stiffness and pulse wave velocity [18,19].

Crucially, most commercially available devices require periodic cuff-based calibration, meaning they track intra-individual changes relative to a baseline rather than measuring absolute BP [20].

Milestones in device development and regulatory recognition

The trajectory of cuffless BP monitoring accelerated alongside mobile technology. Early proof-of-concept studies using smartphone cameras emerged in 2013 [21,22], but systematic reviews confirmed a persistent accuracy deficit, particularly at BP extremes [19].

A decisive regulatory milestone occurred in April 2020, when South Korea’s Ministry of Food and Drug Safety (MFDS) cleared the first smartphone-based blood pressure measurement application. The Korean Society of Hypertension (KSH) responded proactively, publishing the world’s first position paper on smartphone/smartwatch BP measurement in January 2021, defining calibration methods and clinical contraindications [19]. This initiative catalyzed broader international engagement, with the European Society of Hypertension Working Group, American Heart Association (AHA), European Society of Cardiology (ESC), and International Society of Hypertension (ISH) each subsequently issuing formal reviews or scientific statements [23,24,25,26]. On the clinical translation front, the trajectory culminated in June 2024 when CART BP (Sky Labs, Seongnam, Korea) became the world's first cuffless BP device to achieve national health insurance reimbursement—the most direct affirmation that cuffless technology had matured from academic curiosity into regulated clinical practice [27].

The evolution of validation frameworks: building the evidence standard

Defining “accuracy” for cuffless devices posed a fundamental scientific challenge. The standard International Organization for Standardization (ISO) 81060-2:2018 framework, designed for static resting conditions of cuff-based devices, is fundamentally inapplicable to cuffless technologies [20,28,29,30]. When tested immediately after calibration, these devices trivially satisfy static accuracy criteria because they simply reflect the calibration baseline, failing to verify genuine BP tracking capability [20,31].

Dedicated standards evolved sequentially: Institute of Electrical and Electronics Engineers 1708 introduced BP-change induction principles [28,29]; ISO 81060-3 (2022) addressed continuous ICU devices [32]; and the Microsoft Aurora Project (2023) exposed widespread machine learning limitations [33]. Ultimately, the European Society of Hypertension (ESH) Working Group’s 2023 recommendations established the most pragmatic framework to date: 6 rigorous tests covering static accuracy, position, treatment response, awake/asleep changes, exercise, and recalibration stability [30]. An ISO working group (ISO 81060-7) is currently harmonizing these principles into an international regulatory standard [25].

WHAT ARE WE?: THE CURRENT LANDSCAPE – DEVICES, GUIDELINES, AND THE KOREAN EXCEPTION

The global device market: proliferation without validation

Despite the wearable medical device market surging toward $54 billion by 2025 [16], independent validation studies reveal a sobering reality: commercially available cuffless devices frequently fail to reliably track clinical BP changes. Studies demonstrated that Aktiia’s wristband failed to quantify nighttime dipping or track treatment-induced reductions [34,35,36], while Samsung’s Galaxy Watch merely mirrored its calibration value [37,38,39]. As Mukkamala and colleagues [31] concluded in their definitive 2025 review, there is “no compelling evidence that PWA and pulse arrival time can provide significant added value in BP measurement accuracy beyond the cuff BP or demographic data for calibration” [40].

Table 1 summarizes the major regulatory and validation frameworks developed since 2014, illustrating how successive standards have sought to address limitations identified in earlier approaches.

Table 1. Chronological summary of major regulatory and validation frameworks for cuffless blood pressure measuring devices (2014–present).

Year	Organization/document	Device type addressed	Key contributions	Key limitations
2014	IEEE Standard 1708 [28]	Cuffless wearable BP devices (continuous & intermittent)	First dedicated standards requiring BP-change induction.	Lacked specific induction methodologies
2018	AAMI/ESH/ISO Universal Standard (ISO 81060-2:2018) [28]	Automated cuff-based oscillometric BP devices (intermittent)	Cuff-based gold standard	Actively misleading when applied to cuffless validation due to static resting constraints
2022	ISO Standard 81060-3:2022	Continuous cuffless BP devices (beat-to-beat output ≤ 30 seconds)	ICU/OR continuous devices only	Intra-arterial references unfeasible for outpatient use.
2023	ESH Working Group [29]	Intermittent cuffless BP devices	Most actionable framework defining specific tests for automated wearables	Pragmatic but lacks ISO regulatory harmonization
2024–present	ISO (Standard 81060-7) [in development]	Intermittent cuffless BP devices	Expected to harmonize intermittent cuffless validation globally.

IEEE, Institute of Electrical and Electronics Engineers; BP, blood pressure; AAMI, Association for the Advancement of Medical Instrumentation; ESH, European Society of Hypertension; ISO, International Organization for Standardization; ICU, intensive care unit; OR, operating room.

The ESH 2023 6-test framework: the current benchmark

For automated wearable cuff-calibrated devices (ESH device type 2) like CART BP, the 2023 ESH guidelines require five rigorous evaluations [30]: device position test, treatment-induced BP reduction tracking, primary awake/asleep circadian tracking versus ABPM, exercise-induced BP increase, and recalibration stability [24]. Pass criteria demand a mean difference ≤ 5 mmHg and standard deviation ≤ 8 mmHg.

International guidelines versus KSH: from “Not to be” to conditional “To be”

Against the background of pervasive validation failure, all major international hypertension guidelines uniformly counsel against cuffless BP devices for clinical use. The 2025 AHA/American College of Cardiology Guideline for the Prevention, Detection, Evaluation, and Management of High Blood Pressure in Adults recommends “against the use of cuffless BP devices for the diagnosis or management of hypertension until these devices demonstrate greater precision and reliability” [41], and the accompanying 2026 AHA Scientific Statement states explicitly that “currently available devices may be inappropriate for clinical use” [24]. The 2024 ESC and 2023 ESH Hypertension Guidelines reach the same conclusion [42,43]. The 2026 ESC Scientific Statement, representing the ESC Working Group on e-Cardiology, and the ESC Council on Hypertension, and the European Association of Preventive Cardiology, confirms that “due to insufficient accuracy validation, this scientific statement does not recommend their use in clinical decisions” [25]. Citing insufficient accuracy and reliability, these societies maintain a unanimous consensus: without successful, standardized validation, cuffless devices should not be used for hypertension diagnosis or management. At present, the global clinical community’s answer to Hamlet’s question remains definitively “Not to be.”

In a historically unprecedented departure from this consensus, the 2026 KSH Guidelines for the Management of Hypertension formally incorporate cuffless BP devices into clinical practice [11]. The guideline assigns a Class IIb, Level of Evidence (LOE) B recommendation—“usefulness/efficacy is less well established by evidence/opinion”—for cuffless BP devices for out-of-office BP monitoring.

This evidentiary divergence rests on peer-reviewed Korean validation studies of a domestic ring-type cuffless device. These studies successfully demonstrated both static accuracy against auscultatory references and 24-hour ambulatory accuracy comparable to conventional ABPM [44,45]. Furthermore, the guidelines highlight that this device, CART BP, has secured clearance from the MFDS, South Korea’s national regulatory authority for medical devices, and is covered by the National Health Insurance system for 24-hour monitoring [11].

The 2026 KSH Guidelines candidly acknowledge the limitations of their position: “concerns regarding accuracy remain, and these devices have not yet been widely recommended in other international guidelines” [11]. The Class IIb designation—explicitly below Class IIa, which would require more robust evidence—reflects not a dismissal of international concerns but a recognition that accumulating Korean validation data, combined with regulatory and insurance infrastructure unique to the Korean healthcare system, justifies conditional clinical adoption. It is important to emphasize what a Class IIb, LOE B designation does and does not convey. Class IIb explicitly denotes that the usefulness or efficacy of an intervention is less well established by evidence or opinion, and LOE B denotes evidence derived from a limited number of clinical studies rather than multiple, adequately powered outcome trials. Together, these designations formally signal residual uncertainty rather than demonstrated clinical efficacy: the KSH recommendation authorizes conditional use, but it does not certify that cuffless monitoring achieves clinical performance equivalent to validated cuff-based methods. Readers should therefore interpret the 2026 KSH position as a considered clinical judgment permitting cautious, context-specific adoption—one that combines accumulating validation data with expert consensus—rather than as a fully evidence-based endorsement comparable to a Class I or IIa recommendation.

Table 2 provides a domain-by-domain comparison of the rationale behind the international Class III designation and the 2026 KSH Class IIb position.

Table 2. Comparison of rationale for Class III (AHA/ACC 2025, ESC 2024, ESH 2023) versus Class IIb, LOE B (2026 KSH Guidelines, 6th Edition) recommendations for cuffless BP monitoring devices.

Domain	AHA/ACC · ESC · ESH [24,40,41,42]	2026 KSH Guidelines (6th Edition) [11]
Validation compliance	No device has completed the full ESH 2023 6-test protocol.	CART BP completed 2 of 5 ESH tests (Static, Awake/asleep). Treatment and recalibration tests are pending.
BP tracking accuracy	Devices often reflect calibration baseline; failed to track nighttime dip in independent studies.	Met ISO 81060-2 limits for static accuracy and successfully passed the ESH primary awake/asleep test.
Treatment response	No commercial device has successfully detected treatment-induced BP reduction.	Explicitly acknowledged as an evidence gap and the highest-priority pending validation step.
Regulatory and insurance status	Clearances (FDA/CE) often rely on substantial equivalence without full ESH compliance.	Supported by MFDS clearance and the world’s first national health insurance reimbursement.
Outcome and threshold	No RCT outcome data or cuffless-specific normative BP thresholds exist globally.	Acknowledged limitation. Class IIb applies to monitoring only; diagnosis requires cuff-based reference.
Overall recommendation	Class III: Do not use for diagnosis or management of hypertension	Class IIb, LOE B: “Cuffless BP devices may be considered for out-of-office BP monitoring”

AHA/ACC, American Heart Association/American College of Cardiology; ESC, European Society of Cardiology; ESH, European Society of Hypertension; KSH, Korean Society of Hypertension; BP, blood pressure; ISO, International Organization for Standardization; FDA, Food and Drug Administration; MFDS, Ministry of Food and Drug Safety (Korea); RCT, randomized controlled trial; LOE, Level of Evidence.

Beyond device-level data, three specifically Korean factors underpin the KSH position. First, CART BP achieved national health insurance reimbursement following regulatory clearance and an additional review of clinical evidence. Second, leading Korean academic centers have conducted systematic, ESH-aligned validation programs unmatched by other commercial devices globally. Third, the KSH possesses a documented tradition of providing proactive, evidence-informed guidance on emerging technologies—having published the world’s first position paper on wearable BP measurement—and Korea demonstrates a strong capacity for rapid clinical adoption when supported by evidence.

Ultimately, the 2026 KSH Class IIb recommendation does not represent a compromised evidentiary standard. Instead, it offers an honest assessment of a device that is actively satisfying rigorous validation criteria, and foreshadows how international recommendations could evolve as comparable validation and clinical outcome evidence accumulates.

WHERE ARE WE GOING?: THE RESEARCH ROADMAP TO A HIGHER RECOMMENDATION

Completing the ESH validation pathway: updated progress and the global race

As of late 2024, no commercial cuffless device has completed the full ESH 2023 or ISO 81060-3 standards [46]. The gap between device proliferation and validation compliance, documented repeatedly across the literature, remains the defining characteristic of the field.

This situation, however, is beginning to change as multiple manufacturers have initiated ESH-aligned validation programs. Aktiia (Neuchâtel, Switzerland) has progressed most visibly among commercially available devices: the company’s wristband has been studied in a prospective single-centre observational study aligned with the ESH awake/asleep test framework, making it the only device other than CART BP with a published ESH-aligned 24-hour circadian accuracy study [35]. However, Aktiia’s treatment test data demonstrated that the device was unable to detect clinically meaningful BP reductions induced by antihypertensive drug initiation in the COOL-BP study—a formal failure of the most clinically consequential ESH validation test [36]. Biobeat (Israel) has registered a prospective multicenter ESH 2023 awake/asleep validation study (n = 600; ClinicalTrials.gov: NCT07240831), expected to complete in 2026. Prototype investigations using the Aidee Health device have explored BP-change tracking under exercise and laboratory-induced manoeuvres in a framework informed by ISO 81060-3 methodology, though this remains a research prototype rather than a commercial device [46]. CART BP’s validation remains the most advanced. Having successfully published awake/asleep results, its device position and exercise tests are currently under independent peer review (personal communication). The critical treatment-induced change test and full recalibration stability assessments are ongoing. Successful completion and publication of the remaining studies would enable evaluation of the device across all applicable domains of the ESH framework.

Near-continuous monitoring and the redefinition of blood pressure variability (BPV)

Short-term BPV holds massive prognostic value but remains clinically underutilized due to ABPM’s temporal resolution constraints (40–80 readings/day) [47,48]. Near-continuous ring-type devices generate reading densities 15–35 times greater than ABPM, theoretically enabling robust computation of critical metrics like average real variability and morning surges. However, calculating BPV indices from quasi-continuous datasets alters their statistical distributions, demanding the urgent development of independently validated normative ranges for cuffless-derived BPV [47].

The nocturnal dipping problem: a systematic challenge across devices

A systematic challenge across all tested PPG devices is the attenuation of nocturnal BP dipping magnitude compared to ABPM [49]. Mechanistically, this stems from calibration state mismatch: devices calibrated in an awake, seated state cannot recalibrate to the supine posture’s altered venous return and sympathetic tone.

Additionally, conventional ABPM inflations induce micro-arousals and pressor responses during sleep, artificially overestimating nocturnal BP [14,15,50]; cuffless devices lack this artifact, potentially reflecting true sleeping BP more faithfully. Regardless, established ABPM-derived outcome thresholds (e.g., > 10% dipping) [35] cannot be directly applied to cuffless data without risking systematic patient misclassification, making newly calibrated prognostic thresholds a clinical necessity [51].

A quantum leap: the continuous glucose monitoring (CGM) paradigm applied to hypertension

The evolution of BP monitoring mirrors diabetes care. Office BP equates to fasting glucose (snapshot), ABPM to HbA1c (interval trend), while near-continuous cuffless monitoring equates to CGM. By mapping dynamic BP responses passively throughout the circadian cycle, cuffless devices could shift hypertension management toward precision metrics like “BP time in target range,” representing a categorical paradigm shift in cardiovascular care [52].

Normative thresholds and the calibration-regulatory horizon

Beyond technical validation, broader guideline endorsement will require evidence that cuffless BP-guided care improves BP control and reduces hypertension-mediated organ damage and cardiovascular events. The expanding real-world use of CART BP in South Korea may provide a valuable platform for establishing device-specific thresholds linked to hard cardiovascular outcomes, provided that standardized device-derived BP data can be prospectively linked to longitudinal clinical and outcome data [51]. Pragmatic or cluster-randomized trials evaluating cuffless-informed management against standard care will eventually provide the definitive outcome data required for broader guideline integration. Furthermore, the forthcoming ISO 81060-7 standard is expected to provide a harmonized framework for validation and support more consistent regulatory evaluation globally [24,25]. A final consideration concerns calibration itself. Although medical-grade accuracy requires precise individual calibration, the error introduced by the calibration procedure—rather than the intrinsic precision of the sensing hardware—is frequently the dominant contributor to measurement error in cuff-calibrated cuffless devices [31,38]. This raises the possibility that applying machine learning to large demographic datasets could achieve calibration-free estimation, or at least demographic (group-level) calibration, with comparable accuracy while removing the burden and variability of repeated individual cuff calibration; recent demographic-adaptive, calibration-free prototypes have already reported mean absolute errors within ISO-relevant limits [53]. We therefore anticipate that consumer-grade lifestyle devices, in particular, will increasingly evolve toward minimal—demographic—calibration rather than individual cuff calibration, even as clinical diagnostic use continues to require device-specific calibration until calibration-free accuracy is rigorously validated.

Balancing optimism with unresolved limitations

Despite these encouraging validation milestones, several unresolved issues warrant a more circumspect interpretation of current clinical readiness. First, calibration dependency remains the central methodological limitation of cuff-calibrated cuffless devices, including CART BP: because these devices track relative changes from a cuff-derived baseline rather than measuring absolute arterial pressure through an independent principle, their apparent accuracy is inseparable from the accuracy and recency of the calibrating cuff reading itself [38,39]. Second, long-term measurement drift after calibration has not been rigorously characterized; published validation studies, including the awake/asleep protocol completed by CART BP, are largely confined to single monitoring sessions of 24–48 hours, leaving the trajectory of measurement error over weeks to months—and the recalibration interval required to contain it—essentially undefined for any device on the market [38]. Third, validation cohorts to date, including those supporting CART BP, have consisted predominantly of adults free of major arrhythmia and without advanced chronic kidney disease, severe obesity, or pregnancy. Atrial fibrillation and frequent ectopy disrupt the beat-to-beat pulse waveform morphology on which PPG- and PTT-based algorithms depend; advanced chronic kidney disease alters arterial stiffness, vascular calcification, and fluid status; obesity attenuates signal quality and alters cuff-to-sensor geometry; and pregnancy involves substantial hemodynamic and vascular compliance changes. None of these populations has been systematically represented in existing static or awake/asleep validation cohorts, and extrapolating current evidence to them is not justified at present. Finally, and perhaps most fundamentally, no cuffless device—including CART BP—has yet been evaluated in a trial linking device-guided management to hard cardiovascular outcomes or hypertension-mediated organ damage. The 2026 KSH Class IIb recommendation is therefore best understood as a conditional, evidence-informed opinion that authorizes cautious clinical use in a defined regulatory and insurance context, rather than a demonstration of established clinical efficacy. Ongoing and future studies—particularly treatment-response validation, recalibration-stability testing, and dedicated evaluation in arrhythmia, chronic kidney disease, obesity, and pregnancy—will be essential before these limitations can be considered resolved.

SUMMARY AND CONCLUSIONS

Paul Gauguin’s philosophical triptych—Where Do We Come From? What Are We? Where Are We Going?—aptly frames the trajectory of cuffless BP monitoring in 2026.

We emerge from the genuine limitations of cuff-based monitoring and rapid technological innovation that initially outpaced clinical validation. Currently, we exist in a space between incomplete global evidence (International Class III) and progressive, systematic validation that justifies early clinical adoption, as reflected in the 2026 KSH Guidelines’ conditional Class IIb recommendation, which is a conditional judgment that reflects residual uncertainty rather than established efficacy, pending further validation of long-term drift, and performance in special populations such as arrhythmia, chronic kidney disease, obesity, and pregnancy. Looking forward, achieving a continuous, CGM-like paradigm for hypertension depends entirely on completing rigorous treatment response tests, defining cuffless-specific normative thresholds, and proving cardiovascular outcome benefits. The ultimate answer to Hamlet’s question will be written in data. This past–present–future trajectory of cuffless BP monitoring—from the unmet clinical needs that drove its emergence, through the current conditional Class IIb endorsement, to the continuous-monitoring paradigm that will define its future—is summarized visually in Fig. 1.

Fig. 1. The past, present, and future of cuffless BP monitoring. It is framed as a clinical reinterpretation of Paul Gauguin’s triptych “Where Do We Come From? What Are We? Where Are We Going?” The Past (Where Do We Come From?) panel depicts the unmet clinical needs that drove innovation—the burden and sleep disruption of conventional cuff-based ABPM, together with masked and WCH that remain invisible to office BP measurement. The Present (What Are We?) panel represents the current evidentiary balance, in which the 2026 KSH Guidelines issued the world’s first conditional endorsement—a Class IIb recommendation—for cuffless devices in out-of-office BP monitoring, even as major international guidelines maintain a Class III position. The Future (Where Are We Going?) panel envisions 24-hour near-continuous cuffless monitoring as the CGM moment for hypertension, contingent on completing rigorous treatment-response validation, establishing cuffless-specific normative thresholds, and demonstrating cardiovascular outcome benefits.

BP, blood pressure; ABPM, ambulatory blood pressure monitoring; WCH, white-coat hypertension; KSH, Korean Society of Hypertension; CGM, continuous glucose monitoring; AHA/ACC, American Heart Association/American College of Cardiology; ESC, European Society of Cardiology; ESH, European Society of Hypertension; LOE, Level of Evidence.

Abbreviations

ABPM

ambulatory blood pressure monitoring

AHA

American Heart Association

BP

blood pressure

BPV

blood pressure variability

CGM

Continuous Glucose Monitoring

ESC

European Society of Cardiology

ESH

European Society of Hypertension

IEEE

Institute of Electrical and Electronics Engineers

ISH

International Society of Hypertension

ISO

International Organization for Standardization

KSH

Korean Society of Hypertension

LOE

Level of Evidence

MFDS

Ministry of Food and Drug Safety

PPG

photoplethysmography

PTT

pulse transit time

PWA

pulse wave analysis

RCT

randomized controlled trial