However, errors in measuring blood pressure occur often. Most errors result in overestimates of blood pressure, which could cause almost twice as many patients' receiving the diagnosis of hypertension as actually have high blood pressure. In other cases, hypertension is likely underdiagnosed owing to underestimates of blood pressure.
Many errors result in variability of readings and cause confusion regarding blood pressure status.
Currently no evidence exists to support the use of casual readings in assessing a patient's need for pharmacologic treatment. The level of the blood pressure is the main factor in the decision to start antihypertensive therapy. Despite the importance of blood pressure assessments, current guidelines for patient preparation and measurement technique are rarely followed, and the equipment used is often inaccurate. For example, few physicians have patients rest for 5 minutes before blood pressure measurement as recommended. In 3 studies none of the physicians tested followed all the recommendations of the American Heart Association when measuring blood pressure, and few recommendations were followed by more than a minority of physicians.