High blood pressure (hypertension) is defined as a systolic (top number) blood pressure of greater than 140 and/or a diastolic (bottom number) greater than 90. When one of these numbers is abnormal doctors generally consider treatment. However, a single reading indicating a mild abnormality by itself is not enough to merit medication.
About 20 to 25 percent of people with a mildly abnormal blood pressure reading in a doctor’s office have “white coat hypertension,” or blood pressure abnormality only when measured by the physician. Readings done at home or at work are normal.
White coat hypertension does not carry the cardiovascular risks (heart disease and stroke) that regular hypertension does. Documenting home blood pressure requires about 12 measurements over one week that include both morning and evening readings. Of note, normal readings for home determinations (<135/<85) are defined slightly lower than those in a physician’s office.
Additionally, the white coat hypertension effect often wears off with repeated measurement even in the physician’s office. If the doctor notes multiple normal values after an initial elevated reading the initial elevation is not considered evidence of hypertension.
Sometimes the measurement results are quite erratic and the presence or absence of hypertension is unclear. A device that measures blood pressure frequently throughout an entire day can settle the issue. Ambulatory blood pressure monitoring (ABPM) is the best method of defining whether a person has a blood pressure problem.
ABPM measures blood pressure every 15 minutes during the day and every half hour during the night. The nighttime readings are very important since an elevated blood pressure during sleep is a concern.
The ABPM criteria for hypertension are somewhat lower than those for blood pressures taken in a physician’s office: a 24-hour average of 130/80 or above; a daytime average of 135/85 or above; or, a nighttime (sleeping) average of 120/70 or above.
Since blood pressure medication is usually a lifetime commitment it is important to insure that the diagnosis of hypertension is correct.