Equipment and its use is another variable in blood pressure readings. Blood Pressure UK recommends people should use a fully automatic/digital machine that measures upper arm blood pressure; wrist or finger machines can be less accurate.^14,15

Ideally, home test blood pressure machines should be validated against clinical trial protocols.¹⁵ The British Hypertension Society publishes a list of BP monitors validated for home use.¹⁶ It points out that “wrist devices are subject to errors that are not presently evaluated in the available validation protocols.”

In addition, readings for wrist and finger blood pressure meters are dependent on the position of the wrist or finger relative to the heart.¹⁵ A wrist device may meet accuracy criteria “when strict attention is paid to having the wrist at heart level, but in home use this may not happen, and as a consequence the measurement can become inaccurate,” advises the BHS.¹⁷ Finger devices measure a more peripheral blood pressure and can therefore be less reliable, and may not be suitable for patients with narrow or cold fingers.¹⁵

While home test kits are increasingly being used in clinical settings, users need to be aware that standard home use monitors may not be suitable for patients with arrhythmias, pre-eclampsia and certain vascular diseases.¹⁵

In addition, a machine may need to be validated if it is being used for the elderly, for pregnant women or for children, especially if the arm size is smaller than average.¹⁸ Blood Pressure UK also advises that home blood pressure kits should be calibrated at least once every two years, which involves sending them back to the manufacturer and may involve a fee.¹⁴