Secondary hypertension: causes, clues, tests and treatment in the UK

Blood pressure is recorded as two numbers, such as 130/80. The NHS says you are usually considered to have high blood pressure if your reading is 140/90 or higher when checked by a healthcare professional, or 135/85 or higher when checked at home. Most people with high blood pressure have what doctors call primary or essential hypertension, in which no single cause is found.

In secondary hypertension there is a specific, identifiable cause. NICE Clinical Knowledge Summaries say secondary hypertension has a known underlying cause, such as a renal, endocrine or vascular disorder, or the use of certain drugs. The importance of recognising it is that, in some people, treating or removing the cause lowers blood pressure and may avoid lifelong tablets.

As with primary hypertension, untreated high blood pressure puts extra strain on the blood vessels, heart and other organs. The NHS says it can increase the risk of heart disease, heart attacks, strokes, heart failure, kidney disease and vascular dementia.

NICE CKS groups the causes of secondary hypertension as follows. The more detailed list shows how varied the underlying problems are.

The NHS says high blood pressure does not usually cause symptoms, and that many people have it without realising. Rarely it can cause headaches, blurred vision and chest pain. The NHS advises getting help from NHS 111 if you often have headaches or blurred vision, or have chest pain that comes and goes, and calling 999 for sudden chest pain or discomfort that does not go away, as it could be a heart attack.

With secondary hypertension the symptoms of the cause may stand out more than the blood pressure itself. NICE CKS gives examples: intermittently high or labile blood pressure with headaches, sweating attacks and palpitations in phaeochromocytoma; muscle weakness and passing more urine, including at night, in primary hyperaldosteronism; or fatigue, weight gain and constipation in hypothyroidism.

NICE CKS says that while waiting for confirmation of a diagnosis of hypertension a person should be offered investigations for target organ damage and for secondary causes, and an assessment of cardiovascular risk. For adults under 40 with hypertension, specialist evaluation of secondary causes should be considered.

Other triggers include blood pressure that is resistant to treatment, very high readings, a difference in readings between arms, abnormal blood or urine tests, or symptoms of an endocrine condition. NICE CKS advises same-day specialist assessment for a clinic blood pressure of 180/120 mmHg or higher with signs of retinal haemorrhage or swelling of the optic nerve, or life-threatening symptoms, and for suspected phaeochromocytoma.

The NHS explains that a blood pressure test involves a cuff on the upper arm, and that if it suggests high blood pressure you may be asked to use a home monitor or wear a portable monitor that takes readings over 24 hours. NICE CKS says the diagnosis is confirmed with ambulatory or home blood pressure monitoring.

Looking for a secondary cause typically involves blood tests, including kidney function, electrolytes such as potassium, and hormone tests where indicated; urine tests for protein and blood; and imaging such as ultrasound of the kidneys, CT or MRI. NICE CKS adds that renal artery stenosis should be suspected if there is peripheral vascular disease and an abdominal bruit or resistance to treatment, and that primary hyperaldosteronism may present with low potassium.

Treatment has two parts: lowering blood pressure and treating the cause. NICE CKS says management of hypertension includes lifestyle advice, antihypertensive drugs started in a stepwise way, statin treatment where appropriate and annual review. Target clinic blood pressure is below 140/90 mmHg for people under 80, and below 150/90 mmHg for those aged 80 and over.

Treatment of the cause varies. For medicine-related causes this may mean changing or stopping the medicine, only on the advice of a prescriber. NICE CKS notes that after identification of a possible adrenal adenoma, tertiary referral is required for confirmation and possible laparoscopic adrenalectomy, and that people with phaeochromocytoma need specialist care because malignant transformation or catastrophic haemorrhage can be fatal. Alcohol-related hypertension, NICE CKS says, may disappear within a week or two of complete abstinence.

The NHS suggests a healthy, balanced diet, regular exercise, losing weight if overweight, not eating too much salt, drinking no more than 14 units of alcohol a week and avoiding smoking. Lowering blood pressure even a small amount helps reduce risk.

Because causes such as kidney disease, hormone problems or sleep apnoea may need long-term follow-up, keep appointments and bring a list of medicines, including over-the-counter and herbal products such as liquorice, to reviews.

On the NHS, blood pressure checks are available at GP surgeries and many pharmacies, with referral to renal, endocrine or hypertension specialist clinics for suspected secondary causes.

Private endocrinology or hypertension clinics can provide quicker access to hormone tests and imaging. Ask that results go to your GP, because ongoing prescribing and monitoring are usually shared.