Harvard Heart Letter

Ask the doctor: Erratic blood pressure readings

Q. I check my blood pressure at home regularly. My readings are all over the place and different from the reading at my most recent doctor visit. Why is my blood pressure so erratic?

A. There can be many reasons for erratic blood pressure readings. For one thing, blood pressure naturally fluctuates over the course of a day. It is generally lowest when you're sleeping and peaks during the day. If you check your blood pressure at different times, you may be seeing that natural variation. Blood pressure is also affected by physical activity, eating, caffeine, and stress.

To get an accurate picture of your average home blood pressure, use your monitor first thing in the morning and before you go to bed each day for a week. Each time, rest for five minutes in a seated position and then take two or three readings at least one minute apart. Bring the record of your readings and your home monitor to your next doctor's appointment. Your doctor can do a side-by-side comparison of readings from your cuff and the one in the office to find out if the discrepancies lie in the equipment.

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