Have a health care provider check your blood pressure annually. This will ensure accuracy. He or she will measure the pressure of blood in your arteries and detect subtle sounds when your heart contracts and between beats. (Results from automated screening tests such as coin-operated machines are often inaccurate.)
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. Hypertension can be diagnosed after one reading, if this reveals extreme hypertension. In most cases, an extensive work-up is not needed to diagnose hypertension.
The following tests are performed to diagnose hypertension and related conditions:
1. Routine investigations
Physical examination and medical history – confirms the presence of hypertension and determines its severity, evaluates possible damage to organs, establishes the presence of associated diseases that increase the risk of complications and looks 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, blood urea nitrogen 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.
Serum cholesterol – 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 a 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 heart’s size 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:
Doppler duplex ultrasound – a test that uses sound waves to detect narrowing of the arteries that supply blood to the kidneys.
Renal artery angiogram – dye is injected and its course followed through the renal arteries to show any narrowing in the arteries.
Plasma renin activity determination – a blood test that determines the level of renin, a hormone that plays 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.
(Reviewed by Dr B. Rayner, nephrologist)
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