Research has shown that blood pressure readings taken in a doctor’s office can fluctuate from visit to visit, depending on variations in the timing and cuffs used, biological changes, and context:
- Had the patient rushed to the appointment because he was late?
- Did you have a sodium-laden meal for dinner the night before?
- Was the reading taken in a noisy hallway instead of a quiet exam room?
Clinical trials such as the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attacks Trial (ALLHAT) have linked visit-to-visit variability ( VVV) with an increased risk of cardiovascular disease and death. But the scope and real-world implications of VVV were unknown.
A recent retrospective cohort study of more than half a million adults with more than 7.7 million systolic blood pressure measurements sought answers.
Their findings "call into question the way we’ve been controlling blood pressure," lead author Harlan Krumholz, MD, SM, a cardiologist who directs the Yale University Outcomes Research and Evaluation Center, said in an interview. “There is tension between the articles people see in magazines and the experience doctors and patients have in the real world.”
By the numbers
All patients in the study had at least 2 outpatient visits at Yale New Haven Health System between January 1, 2014 and October 31, 2018.
For each patient, the authors compared systolic blood pressure readings between a pair of visits less than 90 days apart. They found that the mean absolute change between 2 consecutive visits was approximately 12 mm Hg, which is higher than the typical reduction that results from antihypertensive medications.
Visit-to-visit variability (VVV) was consistent across patient subgroups defined by demographic characteristics, namely sex, age, race and ethnicity, and medical history. “Notably, there was no subgroup of patients with exceptionally low VVV,” the authors wrote.
Unlike clinical trials such as ALLHAT, the study did not examine the relationship between visit-to-visit variability (VVV) and cardiovascular disease and mortality risk.
“It would be much more interesting if they linked variability to outcomes,” kidney disease and hypertension specialist Paul Drawz, MD, MHS, associate chair of clinical research at the University of Minnesota School of Medicine, said in an interview.
Maintain standards
Cardiologist Franz Messerli, MD, professor of medicine at the University of Bern, cited 2 main reasons for VVV:
- Blood pressure “varies from heartbeat to heartbeat, from winter to summer, from sitting to standing,” Messerli said in an interview.
- And “doctors are terrible at measuring blood pressure,” a fact, he noted, that has been repeatedly documented since at least 1990 . "Lousy blood pressure measurements just aren’t very useful."
Measuring blood pressure in a standardized way helps, as does always asking the patient to sit down and taking 3 consecutive measurements because “the first reading is always too high,” Messerli said. “The cuff takes a while to adjust to the arm.”
His main criticism of Krumholz’s study was that “they didn’t do any standardization at all.”
Drawz led a study that found that blood pressure measurements taken in routine clinical practice were generally higher than those taken in the Systolic Blood Pressure Intervention Trial (SPRINT). The finding, published in JAMA Internal Medicine in 2020, highlighted the importance of a proper technique for measuring blood pressure, the researchers wrote.
Krumholz and his co-authors said they recognized that VVV in their real-world study, with its lack of standardization in blood pressure measurement, might be expected to be higher than that seen in a clinical trial.
However, they noted, that was not the case. The mean visit-to-visit variability (VVV) in their study was similar to the mean ALLHAT quintile, as were the quintiles in both studies, suggesting that "greater standardization of physician-measured blood pressure may not further decrease this variation."
Krumholz and his co-authors acknowledged that their study, published in Circulation: Cardiovascular Quality and Outcomes , had limitations:
- In the data available to them, only 1 blood pressure reading was documented for each office visit; They could not determine whether that number was an average of 2 or more blood pressure readings in a single visit.
- They did not consider the timing, context, or seasonal changes of blood pressure measurements.
- They used prescription data to determine treatment and did not know whether patients were actually filling their prescriptions and taking their medications. Previous research has found that about half of patients with hypertension do not take their medications as prescribed, they noted, so they may have overestimated the true post-treatment VVV.
- Patients were taken equally, regardless of how many visits they had, which could have resulted in overestimation or underestimation of VVV in the cohort.
DIY blood pressure monitoring
The study suggests that visit-to-visit variability (VVV) may be leading doctors to unnecessarily prescribe or increase doses of antihypertensive medications, Krumholz noted.
Although the U.S. Preventive Services Task Force and the American College of Cardiology/American Heart Association (ACC/AHA) recommend against this, "we largely still use office measures." as the main information for most people," Krumholz said. By relying on office-based measurement, “we could be reacting too much to the noise rather than the signal,” she added.
A recent research letter in JAMA Network Open supports Krumholz’s assessment that doctors and patients rely too much on in-office blood pressure readings alone. In a survey of a nationally representative sample of adults ages 50 to 80, the authors found that only 47.9% of respondents with hypertension or a blood pressure-related health condition reported controlling their blood pressure with regularly, although 61.6% said their doctors advised them to do so.
Two methods are used to measure blood pressure outside the office :
- Ambulatory blood pressure monitoring (ABPM) is preferred because it records blood pressure continuously over a 24-hour period, when the patient is awake and asleep. “You can see if they’re submerging at night,” Steven Nissen, MD, chair of cardiovascular medicine at the Cleveland Clinic Lerner School of Medicine, explained in an interview. Not bathing at night is associated with an increased risk of cardiovascular disease. In Switzerland, the ABPM “is reasonably well reimbursed, so we can do it” with all patients before they start hypertension treatment, Messerli said. However, Krumholz and his co-authors noted, ABPM is currently not accessible to many U.S. patients. And Drawz said some patients find that using a cuff and a small device on a strap or on their belt for ABPM is "quite a bit heavy".
- Home blood pressure monitoring requires patients to purchase a well-fitting cuff and wear it several times a week. “I don’t want to drive people crazy, but I think they can incorporate it into their routine,” she said. Nissen noted that "[f]almost everyone can take their blood pressure at home." When she tries to establish patients’ optimal medication dosage, she asks them to measure their blood pressure in the morning and evening. Once they do well on a stable dose, Nissen said, "a couple of days a week is fine." Drawz asks patients to obtain 2 blood pressure readings in the morning and 2 in the evening every day for a week before their appointment. The average of all the readings guides you in managing your hypertension. “Unless they are symptomatic, you hardly need a clinical measurement,” Drawz said.
The precise relationships between office readings and ambulatory blood pressure monitoring and home blood pressure monitoring are "shaky ," according to ACC/AHA recommendations, "but there is general agreement" that the In-office readings are often higher than those obtained outside the office , especially in patients with higher blood pressure to begin with.
“Home blood pressure measurements are excellent as long as the patient does not embellish the results,” Messerli noted. He said he has seen patients who, to please him, dismiss a high blood pressure reading in his office as white-coat hypertension and then manipulate the numbers on their home readings to make them appear not to be elevated.
For some, blood pressure cuffs are uncomfortable, Krumholz said, so the holy grail for taking measurements outside the doctor’s office would be cuff-free devices that patients barely know are there. “I hope innovation comes to our rescue.” (Cardiologist Eric Topol, MD, founder and director of the Scripps Research Translational Institute , recently wrote about his test drive of one such device, a bracelet that is not yet available in the US.)
The result
“The take-home message of this paper is not necessarily what factors are associated with variability, it’s just that there is a lot of variability ,” Drawz said. "This confirms the importance of multiple blood pressure readings... and the importance of proper blood pressure measurement."
