In-Clinic and Out-of-Clinic BP Monitoring

During my Hypertension Clinic this week, I had a virtual follow-up appointment with an elderly female patient with a previous diagnosis of hypertension. However, during a recent hospital admission, her blood pressure medication had been discontinued since her blood pressure was within normal limits during her hospital stay. Since her discharge from hospital several months ago, she was no longer taking any blood pressure medications, but also had not been monitoring her blood pressure at home. During my virtual appointment, I counselled her around the importance of regularly monitoring her blood pressure by purchasing an at home blood pressure monitor from the drug store.  We scheduled a follow-up appointment in 4 weeks time and I asked that she record her blood pressure measurements twice a day (once in the morning and once in the evening) for one week leading up to her next appointment. The patient asked me whether she could just come into clinic in 4 weeks time and have her blood pressure taken by us in clinic. This gave me a chance to reflect and learn more about the accuracy and utility of at home vs. clinic blood pressure measurements.

Traditionally, especially in primary care settings, BP measurements that are used to diagnose patients with hypertension or assess the efficacy of BP-lowering medications are often obtained in the clinic setting. However, past studies have indicated that clinic BP measurements can often result in over- or under-estimates of a patient’s true baseline BP over time. Patients who have white-coat hypertension have elevated clinic BP but normal at home BP measurements. This is often attributed to anxiety from seeing a healthcare provider or being in a clinic setting. On the other hand, patients who have masked hypertension have normal BP in clinic, but elevated at home BP measurements. These patients have been shown to be at enhanced risk of cardiovascular events. The high prevalence of white-coat and masked hypertension within the general population highlights the importance of using both in-clinic and out-of-clinic BP measurements as markers of hypertension control. Other factors that can impact the estimate of true baseline BP include the inherent variability of BP throughout the day. This is another reason why being able to measure BP at home at different times throughout the day and having a larger number of readings provides a more reliable assessment of BP than a single measurement within the clinic.

Out-of-clinic BP measurements can be done with home BP monitors, as I had advised to my patient in this encounter. However, ambulatory BP monitoring is also available as another method. Despite recommendations by various guidelines of ambulatory BP monitoring over home BP monitoring, a systematic review by Shimbo et al. did not find sufficient evidence that either method was superior to the other for predicting cardiovascular risk. Ambulatory BP monitoring, while providing more data points in BP measurements, may not be well-tolerated by patients since the frequent inflation of the BP cuff can interfere with sleep and patients’ other daily activities. As a result, home BP monitoring has typically been more widely used. Home BP monitoring has been demonstrated to be stable and have good reproducibility.

Ultimately, both in clinic and out-of-clinic BP measurements play an important role in the diagnosis of hypertension and assessment of efficacy of anti-hypertensive treatments, and home BP monitoring is a reliable method of obtaining out-of-clinic measurements.

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References:

O’Brien E, Asmar R, Beilin L, Imai Y, Mallion JM, Mancia G, et al.; European Society of Hypertension Working Group on Blood Pressure Monitoring. European Society of Hypertension recommendations for conventional, ambulatory and home blood pressure measurement. J Hypertens 2003; 21:821–848.

Masugata H, Senda S, Inukai M, Himoto T, Hosomi N, Murao K, et al. Clinical significance of differences between home and clinic systolic blood pressure readings in patients with hypertension. J Int Med Res. 2013;41(4):1272-1280.

Shimbo D, Abdalla M, Falzon L, Townsend RR, Muntner P. Studies comparing ambulatory blood pressure and home blood pressure on cardiovascular disease and mortality outcomes: a systematic review. J Am Soc Hypertens. 2016;10:224–234.e17. 

Viera AJ, Lingley K, Hinderliter AL. Tolerability of the Oscar 2 ambulatory blood pressure monitor among research participants: a cross-sectional repeated measures study. BMC Med Res Methodol. 2011;11:59.

Ragot S, Gene`s N, Vaur L, Herpin D. Comparison of three blood pressure measurement methods for the evaluation of two antihypertensive drugs: feasibility, agreement, and reproducibility of blood pressure response. Am J Hypertens 2000; 13: 632–639.