Secondary hypertension: causes of high blood pressure and when to look for them

Most people with high blood pressure have what doctors call primary or essential hypertension, where no single cause is found and age, family history, diet, weight, alcohol and other factors contribute. The NHS lists these risk factors, including being older, having close relatives with high blood pressure, Black African, Black Caribbean or South Asian background, a diet high in salt, being overweight, smoking, drinking too much alcohol and long-term stress. In secondary hypertension, by contrast, a specific underlying condition or medicine is driving the pressure up.

The Manchester University NHS Foundation Trust newsletter, written for GPs by a consultant clinical scientist in biochemistry, puts the scale in context: an estimated 26% to 30% of adults in the UK have hypertension, around 13.2 million people, and up to 10% of those have a secondary cause. Identifying those people lets the specific cause be treated, which may improve control or, in some cases, cure the hypertension.

The trust newsletter sets out the principal groups of causes and the tests that point towards them.

The newsletter lists groups who should be screened: young-onset hypertension, before the age of 40 (citing NICE NG136), drug-resistant hypertension, a sudden deterioration in blood pressure control and hypertensive emergency. It also lists clinical clues.

• Muscle weakness, tetany, cramps or arrhythmias, which may point to primary hyperaldosteronism.

• Rapid-onset acute pulmonary oedema, which may point to renal artery stenosis.

• Sweating, palpitations or frequent headaches, which may point to phaeochromocytoma or paraganglioma.

• Snoring or daytime sleepiness, which may point to obstructive sleep apnoea.

• Symptoms suggesting underactive or overactive thyroid, such as tiredness and cold intolerance, or weight loss and heat sensitivity.

NICE guideline NG136 says to consider the need for specialist investigations in people with signs and symptoms suggesting a secondary cause of hypertension, and, for adults aged under 40 with hypertension, to consider seeking specialist evaluation of secondary causes and a more detailed assessment of the long-term balance of treatment benefit and risks.

In practice the first steps are routine: the blood pressure confirmed with home or ambulatory monitoring, blood tests for kidney function and electrolytes, a urine test for protein, and a review of medicines, alcohol and sleep. The trust newsletter explains that the aldosterone:renin ratio needs careful preparation: low potassium should ideally be corrected first, people should not restrict salt beforehand, and aldosterone antagonists and diuretics should if possible be stopped for 4 weeks. Results can take up to two weeks. Some tests, such as plasma metanephrines, are collected in hospital because the sample must reach the laboratory within an hour.

Never stop blood pressure medicines before a test unless the clinician who requested it tells you to; the newsletter notes that if drugs cannot be withdrawn the sample is still taken and the medicines recorded so that results can be interpreted.

Treatment depends on the cause. The newsletter recommends referral to endocrinology where hormone tests are abnormal. Treating the underlying problem, such as managing kidney disease, treating sleep apnoea or changing a medicine, may reduce blood pressure, and blood pressure medicines are often still used alongside.

Whatever the cause, the NHS advice on reducing risk applies: a healthy balanced diet, regular exercise (at least 150 minutes a week), losing weight if overweight, not eating too much salt, keeping alcohol to no more than 14 units a week, and cutting down on caffeine and smoking. The NHS explains that untreated high blood pressure puts extra strain on blood vessels, heart, brain, kidneys and eyes and raises the risk of heart attack, stroke, heart failure, kidney disease and vascular dementia.

The NHS says to get help from NHS 111 if you often have headaches or blurred vision, chest pain that comes and goes, or other symptoms you worry may be caused by high blood pressure. It says to call 999 for sudden chest pain or discomfort that does not go away, pain spreading to the arm, neck, jaw, stomach or back, or chest pain with sweating, sickness, light-headedness or breathlessness, and not to drive yourself to A&E.

On the NHS, the GP is usually the first point of contact and can arrange most first-line tests, with referral to renal, endocrine or hypertension clinics where a secondary cause is suspected. Private hypertension or endocrine clinics can arrange the same tests more quickly.

Because some tests depend on timing and stopping certain medicines, it helps to coordinate with your GP so that results are interpreted correctly and prescriptions are kept consistent.