Tests and diagnosis

By Mayo Clinic Staff

To diagnose prehypertension, you'll have a blood pressure test. Your doctor or a specialist will usually place an inflatable arm cuff around your arm and measure your blood pressure using a pressure-measuring gauge.

A blood pressure reading, given in millimeters of mercury (mm Hg), has two numbers. The first, or upper, number measures the pressure in your arteries when your heart beats (systolic pressure). The second, or lower, number measures the pressure in your arteries between beats (diastolic pressure).

Your blood pressure is considered normal if it's below 120/80 mm Hg. Other blood pressure measurements are categorized as:

  • Prehypertension. Prehypertension is a systolic pressure ranging from 120 to 139 mm Hg or a diastolic pressure ranging from 80 to 89 mm Hg.
  • Stage 1 hypertension. Stage 1 hypertension is a systolic pressure ranging from 140 to 159 mm Hg or a diastolic pressure ranging from 90 to 99 mm Hg.
  • Stage 2 hypertension. More severe hypertension, stage 2 hypertension is a systolic pressure of 160 mm Hg or higher or a diastolic pressure of 100 mm Hg or higher.

Because blood pressure tends to fluctuate, a diagnosis of prehypertension is based on the average of two or more blood pressure readings taken on separate occasions in a consistent manner. Your blood pressure generally should be measured in both arms to determine if there is a difference. Your doctor may ask you to record your blood pressure at home and at work to provide additional information.

Your doctor may suggest a 24-hour blood pressure monitoring test called ambulatory blood pressure monitoring. The device used for this test measures your blood pressure at regular intervals over a 24-hour period and provides a more accurate picture of blood pressure changes over an average day and night. However, these devices aren't available in all medical centers, and they're rarely reimbursed.

June 23, 2015