Secondary hypertension

Before investigating for secondary causes of elevated blood pressure (BP), confirm that the recorded BP is indicative of the patient’s true BP (see Measurement of blood pressure) and exclude nonadherence with BP-lowering drugs.

If there is clinical suspicion of a secondary cause, it is best to investigate before starting BP-lowering therapy. This is to identify treatable causes and avoids the need to withhold established treatments that may interfere with certain investigations (eg the aldosterone–renin ratio).

Secondary hypertension is often difficult to control with standard BP-lowering therapy so should be suspected in patients who have apparent resistant hypertension. Secondary hypertension should also be suspected in patients with:

symptoms or signs suggestive of a secondary aetiology (eg palpitations, haematuria, delayed femoral pulse, epigastric bruit)
abnormal biochemistry findings (eg low potassium or elevated creatinine plasma concentration, proteinuria, haematuria)
abnormal diagnostic imaging (eg computed tomography [CT] angiography showing renal artery stenosis, CT scan showing adrenal mass).

In adults, the most common curable cause of secondary hypertension is primary aldosteronism (even in the absence of electrolyte disturbance), which accounts for around 10% of adults with hypertension. Other common secondary causes include renal artery stenosis and renal parenchymal disease.

Note: The most common curable cause of secondary hypertension in adults is primary aldosteronism.

Other causes to consider (particularly if clinical findings are indicative) are thyroid dysfunction, Cushing syndrome, phaeochromocytoma and coarctation of the aorta. Drug-induced hypertension is also an important (and often overlooked) cause of secondary hypertension. Sleep apnoea can also contribute to treatment-resistant hypertension.

In children, elevated BP is likely to be due to a secondary cause. Elevated BP in children requires specialist evaluation and treatment.