Real-World Performance of a Ring-Type Cuffless Blood Pressure Device Compared With Ambulatory Blood Pressure Monitoring

Objective: Cuffless blood pressure (BP) monitoring devices offer a potential alternative to conventional cuff-based ambulatory BP monitoring (ABPM), but their real-world performance across diurnal and nocturnal periods remains unclear; we therefore aimed to evaluate the agreement of a ring-type cuffless device (CART) with ABPM over 24-hour, daytime, and nighttime periods and its accuracy for nocturnal hypertension and dipping phenotypes.Design and method: We conducted a prospective simultaneous monitoring study in 154 of 168 enrolled adults (mean age 62.1 ± 14.2 years, 41.6% men) after excluding those with predefined clinical conditions or insufficient valid readings, in whom both conventional ABPM and a cuffless wearable device (CART) were worn over 24 hours. CART measurements were initiated after calibration to ABPM on the opposite arm. BP values were compared for 24-hour, daytime, and nighttime periods using mean differences and Bland–Altman analysis. Agreement for nocturnal hypertension and dipping status was evaluated using Cohen's kappa. Factors associated with close agreement (|24-h SBP difference| <5 mmHg) were analyzed using multivariable logistic regression. Results: CART systematically underestimated systolic BP and overestimated diastolic BP compared with ABPM. For 24-hour SBP, CART values were 7.1 mmHg lower than ABPM (SD of difference 10.6 mmHg), with only 33.1% of subjects meeting the <=5 mmHg accuracy criterion. Daytime SBP showed a similar bias (–7.8 mmHg), whereas nighttime SBP differences were smaller (–1.7 mmHg). In contrast, diastolic BP was consistently higher on CART, particularly at night (+4.8 mmHg). Classification agreement for nocturnal hypertension was moderate (k=0.516, McNemar p=0.324), while dipping pattern concordance was limited, with CART showing significantly attenuated dipping (mean 3.7% vs 7.8% by ABPM). In multivariable analysis, older age (OR 1.04 per year), male sex (OR 2.57), and lower BMI (OR 0.88 per kg/m2) independently predicted close SBP agreement, whereas higher heart rate was also associated with better concordance (OR 2.19). Conclusions: CART showed moderate agreement with ABPM, particularly for heart rate and nocturnal hypertension, but systematic systolic BP underestimation and attenuated dipping—especially in younger and higher-BMI individuals—limit its reliability for hypertension phenotyping, indicating that calibration and further validation are required before clinical substitution.