Your blood pressure varies by quite a lot during the course of a typical day, depending on your activity level, fluid status, anxiety level, and and many other constantly changing factors. For instance, during intense exercise your blood pressure often (and normally) rises to levels that would be considered alarming at rest. So when diagnosing hypertension, your blood pressure must be measured under controlled and reproducible circumstances. Practically speaking, this means measuring your blood pressure under a condition of "quiet rest."
Measuring Blood PressureIt is important that your doctor make sure that the blood pressure measurement he or she is recording reflects a true "resting" blood pressure. The guidelines for achieving a resting blood pressure measurement have been spelled out:
Your blood pressure should be recorded in a quiet, warm environment, after you have been sitting quietly for at least five minutes. You should not have used caffeine or tobacco products for at least 30 minutes. The doctor should take at least two blood pressure readings, preferably at least five minutes apart, and if the readings vary by more than 5 mmHg, further readings should be done until they agree.
Using this method for measuring blood pressure, a diagnosis of hypertension should require at least three elevated blood pressure readings, taken at least one week apart.
In some cases, instead of attempting to achieve a resting blood pressure measurement in a physician's office, it may be advantageous to use ambulatory blood pressure monitoring (ABPM), which is a method of recording numerous blood pressure readings over a 24- to 48-hour period.
It has also become popular in recent years for people to measure their own blood pressure at home. Occasionally it can be very helpful to do this. But, given that blood pressure measurements are so sensitive to circumstances, interpreting home blood pressure recordings can be as difficult as (or more difficult than) interpreting the recordings in a doctor's office. If you want to do home blood pressure measurements, you should try to do it in cooperation with your own doctor.
When Is Hypertension Diagnosed?
Once your blood pressure is measured accurately, your doctor will classify the results, depending on your systolic and diastolic blood pressure values, as follows:
- Normal blood pressure: systolic less than 120 mmHg, AND diastolic less than 80 mmHg
- Hypertension: systolic 140 or higher, OR diastolic 90 or higher
- "Prehypertension:" blood pressure readings lie between the normal and the hypertension ranges.
- Stage 1 hypertension: systolic no higher than 159 mmHg, AND diastolic no higher than 99 mmHg
- Stage 2 hypertension: systolic greater than 159 mmHg, OR diastolic greater than 99 mmHg
If you have hypertension, in general the goal of therapy is to restore your blood pressure to well below 140/90. If you have heart disease, diabetes, or kidney disease, however, therapy tends to be more aggressive; the goal is usually to restore blood pressure to below 120/80.
If you have "prehypertension," you are reasonably likely to develop true hypertension within a few years. You should talk to your doctor about non-pharmaceutical steps to reduce your blood pressure, and you should also make sure you have your blood pressure re-checked every six to 12 months.
What About "White Coat Hypertension"?Some patients will have elevated resting blood pressures in the doctor's office, but will have normal resting blood pressures at other times. This pattern has been called "white coat hypertension."
What About "Malignant" or "Urgent" Hypertension?"Malignant" hypertension is present when the diastolic blood pressure is very high, usually 120 mmHg or greater, and in addition there are signs of acute blood vessel damage caused by hypertension. Most commonly, the blood vessel damage in malignant hypertension can be detected by examining the blood vessels in they eye, through an ophthalmoscope. Malignant hypertension is a medical emergency, since it often leads to acute damage of the heart, brain, kidneys and eyes. It requires immediate hospitalization and aggressive treatment to get the blood pressure under rapid control.
Chobanian, AV, Bakris, GL, Black, HR, Cushman, WC. The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: The JNC 7 Report. JAMA 2003; 289:2560.
# Staessen, JA, Wang, J, Bianchi, G, Birkenhager, WH. Essential hypertension. Lancet 2003; 361:1629.