AIM Feature: BP measurement too casual, guidelines needed
The study authors called the ability to treat high BP one of the “greatest medical advances,” but they also wrote that “a person’s underlying true BP is not readily available at the point of care, and the clinician must infer the true value on the basis of a small number of measurements from either the clinic or the home.” Often, clinic BP measurements approximate a patient's true BP, and clinic measurements with nonmercury devices fall short “because of the measurement technique or observer effects,” wrote Benjamin J. Powers, MD, of the Durham VA Medical Center in Durham, N.C., and colleagues.
To determine the optimal setting and number of BP measurements that should be used for clinical decision making, Powers et al evaluated 444 veterans with hypertension for 18 months. Blood pressure measurements were taken using three methods: standardized research BP measurements at six-month intervals; clinic BP measurements obtained during outpatient visits; and home BP measurements using a monitor that transmitted measurements electronically.
“Whether you used research measurement, home measurement or clinic measurement made a big difference whether you classified patients as in or out of control,” Powers, the study’s lead author, said in an interview. “For all of these settings, the inherent variability was basically the same. Readings between 120 and 160 mm Hg required multiple measurements to be averaged together to be able to confidently classify patients as in or out of control.”
During the study, patients provided 111,181 systolic BP measurements (3,218 research, 7,121 clinic and 100,842 home measurements). Systolic BP control rates varied, with 68 percent classified as in control percent by research measurements, 28 percent with clinic measurements and 47 percent by home measurements.
In addition, the researchers reported that the relationship between mean clinic and home systolic BP. For example, 51.6 percent of patients had a mean clinic systolic BP of at least 10 mm Hg greater than their mean home SBP and 5 percent of patients had a mean clinic systolic BP at least 10 mm Hg less than their mean home systolic BP.
“Patients could not be classified as having BP that was in or out of control with 80 percent certainty on the basis of a single clinic SBP measurement from 120 mm Hg to 157 mm Hg,” the authors wrote.
Currently, there is no consensus among the clinical guidelines and quality-reporting standards on the setting, timing and total number of BP measurements to be used to make clinical treatment decisions, the authors wrote.
In an accompanying AIM editorial, Lawrence J. Appel, MD, MPH, and colleagues from the Johns Hopkins University in Baltimore, wrote that “in practice, BP measurement is remarkably casual.” Appel and colleagues wrote that clinicians and patients observe “major deviations from accepted standards,” such as BP cuffs being applied over clothing or BPs obtained without the patient resting for five minutes.
The latest report from the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure recommends identifying hypertension by two or more seated clinic measurements; however, the authors said that the report does not outline the most optimal way to measure ongoing blood pressure treatment or management.
“Currently, we evaluate hypertension by taking a patient’s clinic blood pressure at a single visit using the minimal number of measurements and then decide whether a patient was in or out of control,” Powers said.
During the study, Powers and colleagues found that one clinic measurement of 132 mm Hg had a 40 percent probability of having a true SBP of 140 mm Hg or more. However, five clinic measurements at 132 mm Hg would have less than 18 percent probability of a true SBP of 140 mm Hg or more. The researchers therefore concluded that most mean systolic BPs could be categorized with 80 percent probability based on the mean of five home measurements.
“In most settings, if you could get five to six readings you would be able to categorize patients as being in or out of control. The closer patients are to the goal blood pressures, the more measurements it will take,” Powers said.
Powers said that home monitoring may be the right solution to obtain these increased measurements. “These monitors could make doctors' decision-making process simpler by providing a range of information about the patients’ blood pressure.”
Due to the variability between mean and clinic BP and the inherent within-patient variability of BP, clinicians currently lower treatment goals for home BP by 5 mm HG. “We shoot for a lower blood pressure at home than we do in clinic. This 5 mm Hg correction is a rough rule of thumb for most patients and the point of that part is to design studies to understand what the best BP goal is.”
While Powers and colleagues offered that patient variability could be reduced with more frequent clinic measurement, they said that this would still not eliminate “white-coat effects” and may not be practical for most patients and providers.
“We can make a patient’s care much more personalized and tailored just by collecting more information on how blood pressure differs from the clinic and home,” said Powers. “Collecting this information and aggregating measurements at the individual level would allow doctors to make more informed decisions,” Powers concluded.
Appel et al said that the implications of the study are substantial. “Spuriously high clinic readings could lead to inappropriate addition or escalation of antihypertensive drug therapy and increased risk for adverse drug effects. If used as quality metric, single measurements of clinic BP might lead to an erroneous assessment of provider performance,” the authors wrote.
While Appel et al offered that education will not solve the problem; they added that EHRs and other clinical decision support tools could help electronically capture and average blood pressure measurements to help guide treatment. The authors urged the Joint Commission and other organizations to set standards and monitor compliance.