Hypertension is usually diagnosed during a general physical check-up, or a visit to the doctor for some other complaint - sometimes a person may be diagnosed as having had a stroke or a heart attack and are then found to have high blood pressure. Blood pressure is measured is by using an instrument called a sphygmomanometer, which has an inflatable cuff that is wrapped around the upper arm and inflated with air via a rubber bulb that is repeatedly squeezed. When the pressure in the cuff gets high enough, it cuts off the blood flow in the main artery of the upper arm - the air is then slowly released from the cuff via a valve and as the pressure in the cuff falls sounds of the blood rushing through the artery are heard through a stethoscope placed over the artery. The pressure at which sound is first heard as the cuff is released is the systolic pressure and the pressure at which the last sound is heard, as the blood returns to its silent, unimpeded flow – is the diastolic pressure. Automatic electronic measuring devices do the same thing but are more accurate, easier to use, and can be used by patients for home blood pressure monitoring.
A doctor will not diagnose hypertension on the basis of one abnormal reading because blood pressure fluctuates and it usually takes three consecutive abnormally high readings, taken on different occasions, before a diagnosis of hypertension can be made. The point at which a high blood pressure reading is considered abnormal will depend on a person's age - experts suggest that people under the age of 65 years should have a blood pressure at rest of no greater than 130/85 mm Hg - and those over 65 years of age should aim for a blood pressure reading of no more than 140/90 mm Hg. When a person's blood pressure is seen to be consistently high, a doctor will carry out a physical examination to check whether any underlying disease could be the culprit and to also check whether there are signs of damage to the body's organs such as absent pulses in the limbs, evidence of artery disease in the retina of the eye, or microscopic traces of blood in the urine (a sign of kidney disease).
Even if the blood pressure is found to be normal after three checks it must still be checked on a regular basis as it can change and the earlier hypertension is diagnosed and brought under control, the less damage there will be to the heart, brain, kidney and other organs.
Those with no personal or family history of the condition should have a check every two years and during routine visits to a doctor - those with a personal or family history of high blood pressure, stroke or heart attack should be checked more frequently.
For children, high blood pressure is determined by comparing the child’s blood pressure with the distribution of blood pressure for children of similar sex, age and height.