It is well established that essential or primary hypertension is an independent cardiovascular risk factor with a poor long-term prognosis if not adequately controlled.
But what about secondary hypertension? Is it worth investigating if the patient will be treated for primary hypertension anyway?
Often underestimated, recent epidemiological studies show that secondary hypertension may be present in up to 10% of hypertensive patients seen in outpatient consultations. The most common causes include primary hyperaldosteronism, renal artery stenosis, and obstructive sleep apnea syndrome. Less frequent but also important to investigate are hypercortisolism, hyperthyroidism, pheochromocytoma, hyperparathyroidism, and aortic coarctation. The collaborative work between the general practitioner and the cardiologist is essential for identifying secondary hypertension, and this assessment can often begin on an outpatient basis, even before referring the patient to a university center if needed.
Once hypertension is confirmed using home blood pressure monitoring or 24-hour ambulatory blood pressure monitoring (ABPM), a systematic evaluation to rule out secondary causes is recommended. To initiate a targeted workup, the following red flags should be identified:
- Early-onset hypertension (<40 years)
- Hypokalemia on initial lab work (serum potassium <3.6 mmol/L)
- Resistant hypertension
- Severe hypertension at first presentation
- Hypertension with significant target organ damage (heart, kidneys, eyes, brain)
- Hypertension associated with an adrenal incidentaloma
A standard diagnostic workup for secondary hypertension includes both imaging and laboratory investigations:
Imaging:
- Echocardiography to assess for left ventricular hypertrophy and rule out aortic coarctation.
- Renal duplex ultrasound to exclude renal artery stenosis (particularly in older patients) and/or MR angiography if fibromuscular dysplasia is suspected.
- Abdominal CT or MRI to identify a potential adrenal adenoma.
Laboratory tests:
- Plasma aldosterone and renin levels under standardized conditions to detect primary hyperaldosteronism. In practice, ACE inhibitors or ARBs should be discontinued two weeks before testing, and mineralocorticoid receptor antagonists at least three weeks prior.
- Plasma and urinary metanephrines to screen for pheochromocytoma.
- Overnight dexamethasone suppression test for suspected hypercortisolism.
- Additional tests: TSH and PTH.
Identifying a secondary cause of hypertension can significantly improve patient outcomes—particularly in cases of unilateral primary hyperaldosteronism or relevant renal artery stenosis, where treatment may be curative. For example, at the same blood pressure level, a patient with primary hyperaldosteronism has a higher risk of cardiovascular complications than a patient with primary hypertension.
In summary, the joint efforts of internists and cardiologists are essential to diagnose the underlying causes of hypertension and improve its prognosis. Secondary hypertension is more common than it appears, and the challenge lies in appropriately identifying which patients warrant a comprehensive evaluation.
Reference:
2024 ESC Guidelines for the management of elevated blood pressure and hypertension
L’HTA secondaire : un “must-have” diagnosis pour les cardiologues - Réalités Cardiologiques
