Updated 06 October 2014

Diagnosing hypertension

Hypertension is diagnosed only after several careful measurements show that the systolic and/or diastolic blood pressure is consistently above normal.

 Hypertension is diagnosed only after several careful measurements show that the systolic and/or diastolic blood pressure is consistently above normal. This is because normal blood pressure fluctuates and stressful situations, such as a visit to your doctor’s rooms, can elevate your blood pressure temporarily. Note that in most cases a single reading is not sufficient and the effect of white-coat hypertension may be underestimated. In most cases an extensive work-up is not needed to diagnose hypertension.

How blood pressure is measured

Blood pressure is measured using a sphygmomanometer. It consists of a soft cuff, wrapped around your upper arm, then inflated to put pressure on the arm and on the brachial artery that runs the length of the limb. This is linked to a column of mercury with precisely calibrated numbers A stethoscope is placed on the inner side of the elbow crease, just below the cuff. This is right above the main artery (the brachial artery) in your arm. Until a couple of years ago the manual method was the norm: listening to the heartbeat over the brachial artery on the inside of the upper arm while deflating the cuff and watching the mercury column fall. When the heartbeat became audible, it meant the pressure is just not high enough to cut off the blood flow in your brachial artery. The point at which this happens is measured and is counted as your systolic pressure. Releasing the pressure even more causes disappearance of the heart beat, and this is the diastolic pressure.

But in recent years new, automated blood pressure monitors that can accurately measure your blood pressure through electronic signals have become the new gold standard. Several readings from an automated blood pressure monitor from a reputable manufacturer are more reliable than any manual reading. Automated blood pressure monitors for use by the health care professional and at home are available. Devices that measure blood pressure at the wrist are not recommended.

Whether blood pressure is measured manually or with an automated machine, blood pressure should always be measured in the upper arm in quiet surroundings. The cuff needs to be the correct size and the subject needs to sitting with the back supported, the legs uncrossed and on the floor and the arm supported at heart level. Several readings need to be taken every 1-2 minutes until readings stabilise. Initial readings are often higher than later readings and the mean of the final 2 readings should be recorded.
Have a health care provider check your blood pressure annually. He or she will measure the pressure of the blood in your arteries and detect subtle sounds when your heart contracts and between beats. The following tests are performed to diagnose hypertension and related conditions:

1. Routine investigations

•    Physical examination and medical history confirm the presence of hypertension and determine its severity, evaluate possible damage to organs, establish the presence of associated diseases that increase the risk of complications and look for possible causes of secondary hypertension. The doctor will look into your eyes with a special instrument to assess possible damage to the retina.
•    Creatinine and potassium test– A blood test that indicates how well the kidneys are functioning and whether they are damaged.
•    Urine analysis– Abnormalities, such as the presence of blood and protein, give an indication of kidney damage and may suggest that the kidneys are also involved in causing secondary hypertension.
•    Blood glucose (fasting)– Can indicate the presence of diabetes, which increases the risk of complications.
•    Fasting lipogram– Diagnoses high cholesterol, which adds to the risk of complications in the hypertensive patient.
•    Electrocardiogram (ECG)– A recording of the electrical activity of the heart, which indicates the degree of damage to the heart and detects previous heart attacks.

If there is reason to suspect that blood pressure measurements taken in the doctor's rooms do not represent true blood pressure (for example, as a result of white coat hypertension), or if there are large fluctuations in blood pressure, out-of-office blood pressure monitoring over 24 hours may be needed. This can take the form of self-monitoring at home or continuous ambulatory blood pressure monitoring.

The 24 hour monitor is now considered a highly accurate and reproducible investigation and predicts outcome far more accurately than office blood pressure. It is not routinely advised but used for special situations. It must be remembered that a daytime mean blood equivalent to office 140/90 is 128/83.

2. Special tests to detect organ damage

Other tests may be done to determine if hypertension has caused damage to the heart or kidneys, or if the person has had a stroke:
•    Chest X-ray– Shows the size of the heart and presence of fluid in the lungs.
•    Echocardiogram– A live image of the heart and its contractions on a television screen.
•    CAT or MRI scans– Computerised axial tomography or magnetic resonance imaging can show damaged brain tissue in a patient who has had a stroke.

3. Tests to detect causes of secondary hypertension

Tests that may be done to check for causes of possible secondary hypertension, such as kidney artery problems (renovascular disease) or hormonal (endocrine) problems, include:
•    Renal and duplex doppler ultrasound– A test that uses sound waves to detect narrowing of the arteries that supply blood to the kidneys and signs of kidney disease.
•    CT or direct renal artery angiogram– Dye is injected and its course followed through the renal arteries to show any narrowing in the arteries.
•    Plasma renin activity and aldosterone determination– A blood test that determines the level of renin and aldosterone, hormones that play an important role in blood pressure control.
•    VMA and norepinephrine test– The levels of these two hormones are high in certain rare tumours of the adrenal glands that result in hypertension.
•    Sleep studies to detect sleep apnoea

Likely course of untreated hypertension

If you have hypertension, your heart works harder than it should to pump blood to distant tissues and organs. If this pressure isn't controlled, your heart enlarges and your arteries become scarred, hardened and less flexible. Eventually your overworked heart may not be able to pump and transport blood properly through stiff arteries.

These changes increase the risk of:

•    Heart disease such as heart attacks (myocardial infarction, or the death of heart muscle)
•    Heart failure (failure to pump enough blood to your body’s tissues and organs to meet their needs)
•    Stroke
•    Kidney failure. Kidney disease is silent and you must insist that your doctor check your kidneys with blood and urine tests.
•    Peripheral vascular disease (any abnormal condition arising in the blood vessels outside the heart) especially to the legs. Peripheral vascular disease may cause cramps in the legs on walking and may even lead to amputation because of lack of blood.
•    Dementia. The connection between hypertension and dementia is increasingly recognised and treatment can delay or prevent dementia.

The risk of complications increases along with an increase in blood pressure, but there is not an abrupt cut-off point above which complications appear. Treatment and follow-up recommendations will depend on factors such as the severity of the hypertension and whether other organs, such as the kidneys, have been affected by it. Organ damage can occur if systolic, diastolic or both pressures are high.

Hypertension can damage the blood vessels that supply blood to the light-sensitive lining of the back of the eye (the retina). This damage, retinopathy, can lead to vision loss or blindness if untreated.

BUT: Hypertension doesn't have to be deadly. It's easy to diagnose and once you know you have it, it can be controlled. Many experts believe that improved detection, treatment and control of hypertension is a major reason why there has been a 50% decrease in death due to heart disease and a 57% decrease in death caused by stroke in America in the last 20 years.

(Reviewed and updated by Prof Brian Rayner, head of the division of nephrology and hypertension, University of Cape Town and Groote Schuur Academic Hospital, November 2010)


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Dr Jacomien de Villiers qualified as a specialist physician at the University of Pretoria in 1995. She worked at various clinics at the Department of Internal Medicine, Steve Biko Hospital, these include General Internal Medicine, Hypertension, Diabetes and Cardiology. She has run a private practice since 2001, as well as a consultant post at the Endocrine Clinic of Steve Biko Hospital.

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