Tell patients who will measure their own blood pressure at home the following:

* Sit in a chair with back support, with feet flat on the floor and arms bared and supported at heart level. Sit next to a table and rest one arm on its surface during measurement. A lack of back and foot support can cause a transient rise in diastolic blood pressure (of, on average, 5 mmHg).

* Rest for at least five minutes before beginning blood pressure measurement. This helps eliminate activity-related factors that can cause elevation in blood pressure.

* It's important to refrain from smoking or ingesting products containing caffeine (such as coffee or tea) for 30 minutes before measurement. Smoking and caffeine ingestion can cause a transient rise in blood pressure.

* Wrap the cuff smoothly and snugly around the upper arm, with the center of the bladder placed directly over the bend in the elbow and the cuff's lower edge placed 2.5 cm (about two finger-widths) above the bend of the elbow. Incorrect cuff placement will yield inaccurate readings.

* Take two or more readings and record the data in a notebook if the monitor isn't memory equipped or linked to a telephone transmission system. Blood pressure changes from one minute to the next; averaging two or more readings taken from the same arm improves the reliability of the data. Frequency of readings will vary according to the severity of the hypertension and the need to monitor or adjust medication dosage.

* Make sure the cuff is sized appropriately. Measure upper-arm circumference before buying a monitor. Using the wrong cuff size results in inaccurate readings.

Asmar R, Zanchetti A. J Hypertens 2000;18(5):493-508Grim CM, Grim CE. In: Izzo J, et al., editors. Hypertension primer: the essentials of high blood pressure. 2nd ed. Philadelphia: Lippincott Williams & Wilkins; 1998. p. 295-8.