• Diagnosing High Blood Pressure (Hypertension)


    Your doctor can diagnose hypertension by checking your blood pressure. It is a very simple test that takes only a few minutes. Usually an inflatable upper arm cuff with a gauge is used. Your doctor or other medical professional will slide the blood pressure cuff to just above your elbow on your bare arm. The cuff will inflate, tightening around your upper arm. Once a measurement has been gathered, the cuff will deflate and your doctor will remove it.

    For the most accurate blood pressure readings:

    • Sit very still with your legs and ankles uncrossed.
    • Relax your arm while they measure your blood pressure.

    There are two numbers that make up your blood pressure reading, which is measured in millimeters of mercury (mmHg):

    • Systolic (sis-TOL-ic) pressure, the first number, measures the pressure as your heart beats and pushes blood through the vessels. A reading of less than 120 is normal; readings over 140 (over 135 if you have diabetes http://www.scai.org/SecondsCount/Disease/Diabetes.aspx) are considered high.
    • Diastolic (DI-a-STOL-ic) pressure, the second number, measures the pressure between heart beats. A diastolic reading below 80 is normal; above 90 indicates high blood pressure (above 85 if you have diabetes http://www.scai.org/SecondsCount/Disease/Diabetes.aspx).


    If your blood pressure is in the prehypertension range, your blood pressure is not as low as it should be for optimal health, but it is not high enough to be called hypertension. Prehypertension is a term used by doctors as a warning, because your blood pressure will likely increase over time. Modifying some lifestyle behaviors may help you prevent or delay the progression to hypertension.


    Once you have hypertension, it is classified into one of two stages. Stage 1 hypertension is an early form of hypertension, although it is still very important to control blood pressure readings in this range. With stage 1 hypertension, doctors may be able to suggest a trial of lifestyle modifications to see if blood pressure can be brought under control before prescribing medications. However, with stage 2 hypertension, the start of medications will usually be required immediately because the blood pressure numbers are more dangerously high and lifestyle changes alone could not bring them down.

    Normal, Prehypertension, and Hypertension Readings

    The chart summarizes the difference between normal blood pressure, prehypertension, and high blood pressure.

      Systolic (mmHg)
    “Top Number”
    Diastolic (mmHg)
    “Bottom Number”
    Normal Blood Pressure less than 120 less than 80
    Prehypertension 120 to 139 80 to 89
    Stage 1 140 to 159 90 to 99
    Stage 2 greater than or equal to160 greater than or equal to100
    One high blood pressure reading is not enough for your doctor to make a diagnosis. Your doctor will need to see you at least three times to see a pattern of high blood pressure readings to diagnose hypertension.
    1. An initial reading will be taken at the first visit.
    2. An average of at least two properly measured readings will be taken at your next visit.
    3. An average of at least two more properly measured readings will be taken at a third visit.

    After your doctor has recorded high blood pressure readings during each of these visits, you can begin to discuss treatment options for hypertension in order to prevent complications. Your doctor may also ask you to keep a log of your blood pressure levels. You can purchase an inexpensive monitor for home use. Of available home blood pressure monitors, those that have an inflatable cuff that goes over the upper arm are typically more accurate than wrist or finger models.

    Arrive at your doctor’s appointment in plenty of time. If you are running late, frustrated because someone took your parking spot, or get lost finding your doctor’s new office, how do you think your blood pressure will respond? If you take medicines for blood pressure, take them as usual on the day of the doctor visit. You would not want your blood pressure to be undertreated because your doctor attributed elevated blood pressure as due to a missed dose of medication.