Hypertension, most commonly referred to as “high blood pressure” or HTN, is a medical condition in which the blood pressure is chronically elevated. It was previously referred to as arterial hypertension; but in current usage, the word “hypertension” without a qualifier normally refers to arterial hypertension.
Hypertension can be classified as either essential (primary) or secondary. Essential hypertension indicates that no specific medical cause can be found to explain a patient’s condition. Secondary hypertension indicates that the high blood pressure is a result of (i.e. secondary to) another condition, such as kidney disease or certain tumors (especially of the adrenal gland). Persistent hypertension is one of the risk factors for strokes, heart attacks, heart failure and arterial aneurism, and is a leading cause of chronic renal failure.
Even moderate elevation of arterial blood pressure leads to shortened life expectancy. At severely high pressures, defined as mean arterial pressures 50% or more above average, a person can expect to live no more than a few years unless appropriately treated.
Hypertension is considered to be present when a person’s systolic blood pressure is consistently 140 mmHg or greater, and/or their diastolic blood pressure is consistently 90 mmHg or greater. Pre-hypertension is not a disease category; rather, it is a designation chosen to identify individuals at high risk of developing hypertension. The Mayo Clinic specifies blood pressure is “normal if it’s below 120/80” but that “some data indicate that 115/75 mm Hg should be the gold standard.” In patients with diabetes or kidney disease studies have shown that blood pressure over 130/80 mmHg should be considered high and warrants further treatment. Even higher numbers are considered diagnostic using home blood pressure monitoring devices.
Diagnosis of hypertension is generally on the basis of a persistently high blood pressure. Usually this requires three separate measurements at least one week apart. Exceptionally, if the elevation is extreme, or end-organ damage is present, then the diagnosis may be applied and treatment commenced immediately.
Obtaining reliable blood pressure measurements relies on following several rules, and understanding the many factors that influence blood pressure reading. For instance, measurements in control of hypertension should be at least one hour after caffeine, 30 minutes after smoking, and without any stress. Cuff size is also important. The bladder should encircle and cover two-thirds of the length of the arm. The patient should be sitting for a minimum of five minutes. The patient should not be on any adrenergic stimulants, such as those found in many cold medications.
Home blood pressure monitoring can provide a measurement of a person’s blood pressure at different times throughout the day and in different environments, such as at home and at work. Home monitoring may assist in the diagnosis of high or low blood pressure. It may also be used to monitor the effects of medication or lifestyle changes taken to lower or regulate blood pressure levels.
Home monitoring of blood pressure can also assist in the diagnosis of white coat hypertension. The American Heart Association states, “You may have what’s called ‘white coat hypertension’; that means your blood pressure goes up when you’re at the doctor’s office. Monitoring at home will help you measure your true blood pressure and can provide your doctor with a log of blood pressure measurements over time. This is helpful in diagnosing and preventing potential health problems.”
Once the diagnosis of hypertension has been made it is important to attempt to exclude or identify reversible (secondary) causes.
Tests are undertaken to identify possible causes of secondary hypertension, and seek evidence for end-organ damage to the heart itself or the eyes (retina) and kidneys. Diabetes and raised cholesterol levels, being additional risk factors for the development of cardiovascular disease, are also tested for as they will also require management.
Blood tests commonly performed include:
- Creatinine (renal function) – to identify both underlying renal disease as a cause of hypertension and conversely hypertension causing onset of kidney damage. Also a baseline for later monitoring the possible side-effects of certain antihypertensive drugs.
- Electrolytes (sodium, potassium)
- Glucose – to identify diabetes potassium
Additional tests often include:
- Testing of urine samples for proteinuria – again to pick up underlying kidney disease or evidence of hypertensive renal damage.
- Electrocardiogram (EKG/ECG) – for evidence of the heart being under strain from working against a high blood pressure. Also may show resulting thickening of the heart muscle (left ventricular hypertrophy) or the occurrence of previous silent cardiac disease (either subtle electrical conduction disruption or even a myocardial infarction).
- Chest X-ray – again for signs of cardiac enlargement or evidence of cardiac failure.