Tests and diagnosis

By Mayo Clinic Staff

Blood pressure is measured with an inflatable arm cuff and 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).

The National Heart, Lung, and Blood Institute says normal blood pressure is below 120/80. Higher readings are classified as:

  • Prehypertension — 120/80 to 139/89
  • Stage 1 hypertension — 140/90 to 159/99
  • Stage 2 hypertension — 160/100 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.

Oct. 10, 2012

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