Most people with high blood pressure have no obvious underlying cause except the usual risk factors such as age, family history, smoking, stressful lifestyle, drinking too much alcohol or being overweight, for example. In these cases, high blood pressure is described as ‘essential’ hypertension.
Secondary hypertension is diagnosed when there is a recognised underlying cause of high blood pressure, so that the high blood pressure is due to another medical condition such as kidney disease, hormone imbalances or the side effects of medication.
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What is secondary hypertension?
One in ten people with high blood pressure have a recognised, underlying cause and are then said to have secondary hypertension. Signs that hypertension may be secondary include:
- a sudden onset of high blood pressure
- a very high blood pressure (for example 180/120 mmHg or higher)
- high blood pressure that is resistant to usual drug treatments
- high blood pressure in someone who is relatively young (less than 30 years or even a teenager), who is not significantly overweight or who has no family history of high blood pressure.
The normal blood and urine screening tests that are requested before starting you on medication will help to identify whether or not your hypertension could be secondary to another health problem.
Secondary hypertension due to kidney disease
The most common cause of secondary hypertension is kidney disease, which accounts for eight out of ten cases. High blood pressure can also lead to kidney disease, however, and it is sometimes difficult to know which condition came first.
When high blood pressure is the cause of kidney disease, it’s usually because uncontrolled essential hypertension hastens hardening and furring up of the renal arteries which supply blood to the kidneys, and damages small blood vessels within the kidneys (and other organs). This reduces blood supply to the kidneys is reduced and they may start to shrink. At the same time, poor blood supply to the kidney filtering units (nephrons) means less urine is produced and kidney function progressively deteriorates as fluid builds up in the circulation. This vicious cycle leads to increasing hypertension and kidney damage.
Poor blood supply to the kidneys also stimulates pressure receptors (baroreceptors) within the kidneys to signal that local blood pressure has fallen. This triggers increased production of a kidney hormone, called renin, which raises blood pressure in an attempt to increase blood supply to the kidneys. Your blood pressure rises even more and a vicious cycle develops.
Where kidney disease comes first, and leads to high blood pressure as a result, this can be due to conditions such as:
- Diabetes complications (diabetic nephropathy)
- Glomerulonephritis (inflammation of the kidney filtration units)
- Atrophic pyelonephritis (shrinking of kidney tissue due to chronic infection or inflammation)
- Polycystic kidneys (abnormal kidney structure due to the formation of multiple cysts during embryonic development)
- Anatomical abnormalities of the circulatory system such as narrowing of the aorta or renal artery (stenosis)
Secondary hypertension due to hormones
Other causes of secondary hypertension include pregnancy, which can lead to pre-eclampsia and eclampsia, as well as other health conditions that mostly involve hormone abnormalities:
- Thyroid problems – either an over or an underactive thyroid
- Polycythaemia, in which blood stickiness is significantly increased due to over-production of red blood cells
- Conn’s syndrome in which levels of aldosterone hormone are raised (aldosteronism)
- Phaeochromocytoma (a rare tumour that secretes excessive amounts of adrenaline/epinephrine and noradrenaline/norepinephrine hormones)
- Cushing’s syndrome (raised corticosteroid levels from overactive adrenal glands or steroid drug treatment)
- Acromegaly (excessive production of growth hormone by the pituitary gland)
- Hyperparathyroidism (over-activity of the parathyroid glands in the neck, which raises blood calcium levels and can damage the kidneys)
Secondary hypertension due to drugs
Several drugs that are available on prescription or bought over the counter from a pharmacy can affect blood pressure and lead to secondary hypertension. Once the side effect is recognised and the medication changed, your blood pressure will usually come down. Known triggers include:
- Nasal decongestants used to reduce a stuffed nose
- Non-steroidal anti-inflammatory drugs (eg ibuprofen) taken to relieve muscle and joint pain. These can raise systolic blood pressure by as much as 5mmHg to 10mmHg and are best avoided if you have hypertension – even if it is well controlled.
- Oral corticosteroids (taken for severe inflammatory conditions such as asthma or rheumatoid arthritis)
- The combined oral contraceptive pill (containing both oestrogen and progestogen hormones) which can raise blood pressure after several year’s use – average increases are 2.8/1.9 mmHg, although higher responses can occur in some women.
If you are taking any medication, check with your doctor or a pharmacist whether or not it is known to affect blood pressure control.
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