Between one-third and one-half of all blood pressure diagnoses made in physicians' offices may be incorrect, according to a study by UBC Psychology Prof. Wolfgang Linden and university colleagues.
It is well known that some people experience a rise in blood pressure in their doctor's office and may be incorrectly diagnosed with hypertension. However, the UBC study also suggests that some patients with high blood pressure appear to have normal blood pressure at a medical office.
The phenomenon, called "white coat normotension," or seemingly normal blood pressure, poses a significant risk to patients, says Linden.
"Many people who think they have normal blood pressure may actually have hypertension," he says.
Patients with false normal blood pressure are very difficult to identify in the physician's office, he adds. Linden and his team found that such patients were more likely to be male, older, former smokers and consume more alcohol.
For the study, the blood pressure of 319 apparently healthy people was measured five times in the office. The subjects also wore a device to measure blood pressure every 20 minutes at home and at work for eight to 12 hours.
For both systolic and diastolic blood pressures--the first and second number in a blood pressure reading--wide disparities were often found. Based on systolic pressure, 23 per cent showed normal pressure in the office but high blood pressure outside the office.
"Diagnoses falling in the borderline range are particularly inaccurate," Linden reports.
The findings suggest that office blood pressure readings were only accurate at diagnosing hypertension, or its absence, if the readings were at least 20 points above or below the recommended cut-off point.
The findings are alarming because even borderline high blood pressure can be dangerous.
Linden suggests that patients could arrive early for a medical appointment and be hooked up to an automatic blood pressure-taking device. Another approach would have patients take their own blood pressure at home.
"If the exclusive use of office blood pressure measurement continues, critical diagnostic errors will be unavoidable," he concludes.