How to interpret a High Blood Pressure Reading

Q - What do the different parts of a high blood pressure reading signify?

A - When blood pressure(BP) is measured, it's written as a fraction.

Systolic BP/Diastolic BP and it is measured in mmHg (Millimeters of mercury)

As you can see from the above illustration of the high blood pressure reading, the numerator or upper number represents the systolic blood pressure while the denominator or lower number represents the diastolic blood pressure.

If the systolic BP is 120 mmHg and the diastolic BP is 70mmHg, then it is written as

120/70 mmHg

But when reporting a high blood pressure reaading verbally, like when you have discussions with your doctor, you say "120 over 70". If it's 140/90mmHg, you say "140 over 90"

Q - What is the normal blood pressure and when is it high?

A - The table below gives the criteria for normal and high blood pressures.

Categories		Systolic BP in mmHg		Diastolic BP in mmHg
Normal Blood Pressure		<120	AND	<80
Prehypertension		120 - 139	OR	80 - 89
High Blood Pressure	Stage 1 Hypertension	140 - 159	OR	90 - 99
	Stage 2 Hypertension	160 and Above	OR	100 and Above

To understand how to interprete a high blood pressure reading, please note the following points:

1. Wherever there is an "AND" it means that the two conditions MUST be met to qualify. E.g. For anyone to have a normal blood pressure, BOTH the diastolic and systolic blood pressures must be below the specified values of 120mmHg and 80mmHg respectively. Therefore 115/75mmHg is normal BUT 145/75mmHg isn't normal because the Systolic BP is high. Also 115/95mmHg isn't normal because the diastolic BP is high.


2. If there is an "OR" it means that whenever one value meets the conditions, then it can fall into that category. E.g. 130/75 is prehypertension because 130 falls in that category. This is true even though the diastolic BP doesn't fall in that category.


3. If the Systolic BP and the Diastolic BP fall into two different categories, then the one that falls into the more severe category determines the class. E.g. A high blood pressure reading of 145/75 mmHg will be stage 1 hypertension in spite of the fact that the diastolic BP (75mmHg) qualifies as normal. This is because the systolic BP of 145mmHg falls into stage 1. In the same vein, 140/105 mmHg will be stage 2 and not stage 1 because the diastolic falls into stage 2.

Q - How is a high blood pressure reading measured?

A - Blood pressure readings are measured using a blood pressure monitor called a sphygmomanometer. You should ask your doctor, or nurse to recommend a suitable one for you.

Q - What is the best time to take my blood pressure?

A - Your blood pressure fluctuates during the day depending on the time and the activity you are involved in. To ensure consistency in your blood pressure readings, you should take your blood pressure at the same time everyday. E.g. In the mornings or at bed time.

Do not take coffee or cigarettes for at least 30 minutes before taking your reading. They contain substances that can affect high blood pressure readings.

Q - Are there any precautions that I should take?

A - In addition to the precautions already mentioned above, you should also know the following.

1. Do not take BP readings when you have a full bladder. Go and empty your bladder and rest for about 5 minutes before you take your reading.
2. If you're anxious, angry or frightened, your blood pressure can be higher than expected.
3. Make sure your arms are properly exposed to give room for attaching the monitor. And try not to wear shirts with tight sleeves as this can affect the reading.
4. Before you take your reading, rest for about 5 minutes, then measure. When you measure, sit on a chair with your back resting on the support, make sure both your feet are on the floor and place your arm and the monitor on a table at the level of your chest. This will provide a result that is closest to what your BP is throughout the day.
5. An average of two different readings taken at least 5 minutes apart is more reliable than 1 reading.

Q - Where Can I get a BP monitor?

A - You can get them at most reputable shops and pharmacies. Ask your health care provider for recommendations.

Published - June, 2006