The European Society of Hypertension guidelines for the management of arterial hypertension define apparent resistant hypertension (RH) as office systolic/diastolic blood pressure (BP) ≥ 140/90 mmHg despite appropriate lifestyle measures and treatment with optimal or best-tolerated doses of three or more antihypertensive agents including a thiazide/thiazide-like diuretic, a renin-angiotensin system blocker and a calcium channel blocker [1]. To diagnose true RH, the inadequate BP control should be confirmed by out-of-office BP monitoring [1]. In this respect 2 factors should be taken into account: First, inadequate BP control in treated hypertensive patients corresponds to values above the office BP threshold of 130/80 mmHg [1] which is the same for daytime ambulatory and home BP [2]. Second, ambulatory and home BP monitoring methods are recommended to identify white coat or masked uncontrolled hypertension and thus to confirm true RH [1]. It should be noted that their diagnostic agreement has been shown to be about 80% and that they present similar cardiovascular prognostic value which is superior to office BP [3, 4]. Therefore, any of these methods can be recommended based on clinical judgment, availability, and patients’ preference [1].

In this issue of the Hypertension Research journal, Seo et al. presented an analysis from a Korean cohort including individuals with apparent RH who were subjected to office, home, and ambulatory BP monitoring [5]. The authors defined “apparent RH” as office BP ≥ 130/80 mmHg with maximum tolerated doses of three antihypertensive agents including a diuretic or any office BP level if treated with ≥4 antihypertensive drugs. Among 823 individuals with RH, 7% had controlled RH, 9% had white coat uncontrolled RH, 15% had masked uncontrolled RH, and 69% had sustained RH based on office and ambulatory BP measurements. Sustained or masked uncontrolled RH was detected in 84% of the participants by ambulatory BP and in 64% by home BP monitoring, with a diagnostic agreement between the 2 methods around 70%. Moreover, 43% of patients with controlled home BP presented nocturnal hypertension although the agreement between home and 24 h BP was similar to that of home and daytime BP.

The study by Seo et al. highlights important issues related to the definition and confirmation of RH [5]. First, the definition of RH was based on office BP ≥ 130/80 mmHg. Although RH regards treated hypertensive patients, its definition has been traditionally based on the office BP threshold for hypertension diagnosis (systolic/diastolic BP 140/90 mmHg) which is not the same as the treatment target threshold (130/80 mmHg) [1]. In line with the office BP thresholds, out-of-office BP thresholds used by Seo et al. corresponded to the office BP treatment target and not to the hypertension diagnosis threshold: 130/80 mmHg for daytime ambulatory and home BP and 125/75 mmHg for 24 h BP. By using these lower office and out-of-office BP thresholds for the diagnosis of RH, its prevalence is expected to rise considerably; however, these lower thresholds reflect current recommendations for office and out-of-office BP control in clinical practice and their employment appears to be reasonable [1].

Second, office BP was measured four times with the average value of the last three measurements used in the analyses and with some of these office measurements being unattended [5]. Moreover, there was a very high prevalence of diabetes (39%) which is more commonly associated with masked hypertension [1]. The above characteristics might explain the higher rate of masked compared to white coat hypertension found in this study.

Third, the diagnostic agreement of ambulatory and home BP was somewhat lower compared to that reported in previous studies conducted in patients with RH [6, 7], mainly attributed to higher ambulatory (daytime systolic/diastolic BP values 139/82 mmHg) versus home BP (130/79 mmHg) levels [5]. The observed moderate agreement might be attributed to various methodological and participant-related issues. The median interval between ambulatory and home BP measurements was 64 days without data on the respective range and order [5]. It could be hypothesized that in some individuals the interval might have been too long so as to affect the reproducibility of BP monitoring methods or even to allow confusion by the seasonal BP variation. Furthermore, age is a major determinant of the ambulatory vs. home BP difference with daytime ambulatory BP being generally higher in younger individuals (job stain, physical activity) and lower in older ones (sedentary lifestyle, orthostatic hypotension) [8]. There is evidence that isolated ambulatory-masked hypertension is much more common in younger participants and isolated home-masked hypertension much more common in older ones [8]. Yet, the average age of the participants in this study was about 60 years which does not justify such a discrepancy between ambulatory and home BP monitoring [5].

Fourth, the majority of individuals with RH exhibited a non-dipping or rising profile and most of them had nocturnal hypertension defined as ambulatory nighttime BP ≥ 120/70 mmHg [5]. Ambulatory BP monitoring is the reference method for assessing nighttime BP, and this constitutes a main disadvantage of home compared to ambulatory BP monitoring [1]. Assessment of the nighttime BP profile may be highly significant in certain categories of individuals such as those with obstructive sleep apnea, chronic kidney disease, diabetes, RH, and/or other comorbidities [1]. Recently, novel low-cost electronic home BP monitors have been developed able to provide nighttime automated BP measurements during sleep [1]. Preliminary evidence suggests that nighttime BP levels obtained by ambulatory or home BP are comparable and most importantly present similar predictive value for preclinical organ damage and cardiovascular outcome [9, 10]. Further research and clinical application of these devices on a wide scale in the future will enhance the diagnostic potential of home BP monitoring and will contribute to a more personalized and tailored diagnostic and therapeutic approach.

In conclusion, the study by Seo et al. offers significant insights regarding the role of ambulatory and home BP monitoring in the setting of RH. Ambulatory and home BP measurements provide valuable information regarding the BP profile; yet, they are not interchangeable and appear to have a complementary role which means that ideally should be both employed, if feasible, especially in high-risk individuals such as those with RH.