Your Blood Pressure Numbers: Lifesavers You Need to Know

While nearly half of all adults in the U.S. have high blood pressure, many have no idea they have the condition, according to the American Heart Association (AHA). However, knowing your blood pressure numbers could help save your life.

That's because high blood pressure, which the AHA calls a "silent killer," usually occurs without any telltale symptoms. When left undiagnosed and untreated over time, the resulting damage to the heart can ultimately prove deadly.

The best way you can find out if you have high blood pressure is to undergo routine blood pressure screenings, the AHA says, so you can know your numbers.

Read more: What Is Blood Pressure, Exactly?

"Blood pressure is a measure of how much pressure the blood is applying against the walls of arteries," explains Gregg Fonarow, MD, director of the Ahmanson-UCLA Cardiomyopathy Center.

"Blood pressure is measured and recorded as two numbers," he notes. "The systolic blood pressure is the top — higher — number recorded, and is the pressure that the blood is applying against the artery walls when the heart is contracting."

"The diastolic blood pressure is the bottom — lower — number recorded, and is the pressure the blood is applying against the artery walls when the heart is not contracting," Dr. Fonarow says.

The other thing to know is that the abbreviation "mm Hg" — the one that's typically indicated after each number in your medical chart — is a reference to "units of millimeters of mercury," Dr. Fonarow says.

Of the two numbers, the systolic blood pressure is the more important reading, he says because "when the systolic blood pressure is elevated, it is more closely associated with an increased risk of heart attack, heart failure, stroke and kidney disease."

Systolic blood pressure rises in most people as they age, the AHA notes. While the upper number does get more focus, having an elevated upper or lower number can be used for a high blood pressure diagnosis, the AHA notes.

Read more: The Best Ways to Lower Your Systolic BP Without Meds

Besides knowing what your numbers are, it's also important to know what's considered a healthy blood pressure reading and what's potentially problematic. According to the AHA, there are five blood pressure categories:

1. Normal. If your upper number stays under 120 and your lower number is below 80, that's considered "normal."
   
2. Elevated. Concern begins when that important upper, or systolic, number registers between 120 and 129, and your lower, or diastolic, number stays under 80. This is an "elevated" blood pressure. People with an elevated blood pressure are likely to go on to develop high blood pressure, the AHA says, unless the problem is addressed.
3. Hypertension stage 1. This category is diagnosed when your higher number falls between 130 and 139 while the lower number edges up to between 80 and 89. The AHA says that people in this category are likely in need of lifestyle changes, such as increasing their activity levels and improving their nutritional habits. In some cases, they may also need prescription blood pressure drugs.
4. Hypertension stage 2. If your numbers hit 140 over 90 or higher, you've entered the fourth category. At this stage, your physician will almost always embark on an urgent treatment plan, including medicine and lifestyle changes.
5. Hypertensive crisis. The last and most worrisome stage is when blood pressure numbers exceed 180 over 120. It's a sign that the person is in need of emergency medical care.
   

The AHA notes that a reading of 180 over 120 that is accompanied by shortness of breath, chest or back pain, numbness or weakness, or vision and speech difficulties can be a particularly urgent situation. In that case, there is only one number you need to know: 911.