High blood pressure or more generally blood pressure is measured with an inflatable arm cuff and a pressure-measuring gauge. The 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 latest blood pressure guidelines, issued in 2003 by the National Heart, Lung, and Blood Institute, divide blood pressure measurements into four general categories:
- Normal blood pressure. Your blood pressure is normal if it's below 120/80 mm Hg. However, some data indicate that 115/75 mm Hg should be the best standard. Once blood pressure rises above 115/75 mm Hg, the risk of cardiovascular disease begins to increase.
- Prehypertension. Prehypertension is a systolic pressure ranging from 120 to 139 or a diastolic pressure ranging from 80 to 89. Prehypertension tends to get worse over time. Within four years of being diagnosed with prehypertension, nearly one in three adults ages 35 to 64 and nearly one in two adults age 65 or older progress to definite high blood pressure.
- Stage 1 hypertension. Stage 1 hypertension is a systolic pressure ranging from 140 to 159 or a diastolic pressure ranging from 90 to 99.
- Stage 2 hypertension. The most severe hypertension, stage 2 hypertension is a systolic pressure of 160 or higher or a diastolic pressure of 100 or higher.
At the age of 50, the systolic reading is even more significant. Isolated systolic hypertension (ISH) — when diastolic pressure is normal but systolic pressure is high — is the most common type of high blood pressure among people older than 50.
A single high blood pressure reading usually isn't enough for a diagnosis. Because blood pressure normally varies throughout the day — and sometimes specifically during visits to the doctor — diagnosis is based on more than one reading taken on more than one occasion. Your doctor may ask you to record your blood pressure at home and at work to provide additional information.
If you have any type of high blood pressure, your doctor may recommend routine tests, such as a urine test (urinalysis)
, blood tests
and an electrocardiogram (ECG)
— a test that measures your heart's electrical activity. More extensive testing isn't usually needed.