Home Blood Pressure Monitors Inaccurate?
Up to a Third May Give Imprecise Blood Pressure
May 16, 2003 (New York) -- As many as one in three people who use home blood pressure monitors to keep tabs on their high blood pressure may be getting inaccurate readings from their devices. A new study shows that up to 35% of home blood pressure monitors provided readings that were considered unacceptable.
Researchers say home blood pressure monitoring is a valuable tool for people with high blood pressure. Taking blood pressure measurements at home can often provide a more accurate assessment because the patient is more comfortable and less likely to experience the temporary rise in blood pressure that accompanies a doctor's office visit, known as "white coat hypertension."
To determine if the readings provided by digital home blood pressure monitors were accurate, researchers asked their high blood pressure patients to bring in their monitors for evaluation. A total of 129 home blood pressure monitors were collected over a period of two years. The results of the study were presented today at the American Society of Hypertension's Eighteenth Annual Scientific Meeting in New York City.
First, all of the home blood pressure monitors were initially screened to see if they had an arm cuff that was the proper size for the user.
"The cuff size can be a significant factor," says researcher Melissa J. Goalen, ARNP, MSN, of the nephrology and hypertension unit at the Mayo Clinic in Jacksonville, Fla. "A cuff that is too small can overestimate high blood pressure, and one that is too big can underestimate high blood pressure."
If the cuff size was unacceptable, further testing was performed using the correct cuff size.
In the second stage of testing, the digital home blood pressure monitors were tested for accuracy vs. a mercury sphygmomanometer, the standard device used in medical offices to measure blood pressure.
If the readings provided by the digital home blood pressure monitor were more than four points under or over the readings of the office device, the monitor was considered inaccurate.
The study found that 24 of the home blood pressure monitors were inaccurate and 13 had unacceptable cuff sizes. Overall, researchers say that meant 35% of the devices tested were not considered acceptable for use.
"Ultimately, we feel that at least one in three home blood pressure monitoring units has the potential if not appropriately checked for size, calibration, and validation of the readings can provide inaccurate information," says Goalen. "This is extremely important because if you have a five [point] overestimation or underestimation of blood pressure in either direction, you can affect the treatment of anywhere from 21 to 27 million people in the country."
Goalen says the accuracy of the home blood pressure monitors tested seemed to vary mostly according to how well the unit had been cared for by the owner. Although home blood pressure monitors are calibrated at the factory, Goalen says they also need to be calibrated and adjusted to fit the individual who will be using the device. She doesn't recommend using wrist or finger units because they cannot be adjusted for the user.
Goalen says people who use home blood pressure monitors should take it into their doctor's office to have the device evaluated and calibrated to ensure that it can provide accurate blood pressure readings.