What investigations are recommended for patients with suspected secondary hypertension?

Investigations for Secondary Hypertension

A thorough diagnostic approach for secondary hypertension should include targeted screening based on clinical suspicion, with specific laboratory tests and imaging studies tailored to the suspected underlying cause. 1

When to Suspect Secondary Hypertension

Secondary hypertension should be considered in patients with:

• Early onset hypertension (<30 years of age), especially in absence of risk factors 1, 2
• Resistant hypertension (BP >140/90 mmHg despite three medications including a diuretic) 1
• Sudden deterioration in previously controlled BP 1
• Hypertensive urgency or emergency 1
• Specific clinical clues suggesting secondary causes 1

Initial Evaluation

Key History Elements

• Symptom patterns: headaches, palpitations, sweating (pheochromocytoma), muscle weakness/cramps (hyperaldosteronism), snoring (sleep apnea) 1
• Medication use and substances that can elevate BP
• Family history of hypertension or endocrine disorders
• Age of onset (early onset suggests secondary causes) 2

Physical Examination Findings

• Abdominal/carotid/femoral bruits (renovascular disease) 1
• Radio-femoral delay (coarctation of aorta) 1
• Neck circumference >40 cm (obstructive sleep apnea) 1
• Cushingoid features (central obesity, striae) 1
• Enlarged thyroid gland 1
• Peripheral edema, basal crackles (heart failure) 1

Basic Laboratory Screening

• Serum sodium and potassium (hypokalemia may suggest hyperaldosteronism) 1
• Serum creatinine and estimated GFR (renal disease) 1
• Fasting blood glucose (diabetes, Cushing's syndrome) 1
• Lipid profile 1
• Thyroid-stimulating hormone (TSH) 1
• Urinalysis (proteinuria, hematuria suggest renal disease) 1
• 12-lead ECG (left ventricular hypertrophy, arrhythmias) 1

Advanced Testing Based on Clinical Suspicion

For Suspected Renal Parenchymal Disease

• Kidney ultrasound (evaluates kidney size, structure) 1
• Urinary albumin/creatinine ratio 1
• Renal function tests 1

For Suspected Renovascular Hypertension

• Duplex ultrasound of renal arteries 1
• CT or MR angiography (depending on renal function) 1, 3
• Consider when: abrupt onset severe hypertension, abdominal bruit, deterioration of renal function with ACE inhibitors 4

For Suspected Primary Aldosteronism

• Aldosterone/renin ratio (initial screening test) 1, 5
• Confirmatory testing (IV saline suppression test) 1
• Adrenal CT imaging 1
• Adrenal vein sampling (to determine laterality) 1

For Suspected Pheochromocytoma

• Plasma free metanephrines 1
• 24-hour urinary catecholamines 1
• Abdominal/adrenal CT or MRI 1, 3

For Suspected Cushing's Syndrome

• Dexamethasone suppression test 1
• 24-hour urinary free cortisol 1
• Late-night salivary cortisol 1
• Abdominal/pituitary imaging 1

For Suspected Obstructive Sleep Apnea

• Home sleep apnea testing (level 3 sleep study) 1
• Overnight polysomnography 1
• Consider when: obesity, large neck circumference, snoring, daytime sleepiness 1, 4

For Suspected Coarctation of Aorta

• Echocardiogram 1
• CT or MR angiogram 1
• Consider in young patients with upper extremity hypertension and diminished femoral pulses 4

For Suspected Thyroid Disease

• Thyroid function tests (TSH, free T4) 1

Age-Based Approach

Children and Young Adults (<30 years)

• Renal parenchymal disease and coarctation of aorta are most common causes 4, 5
• In young women, fibromuscular dysplasia should be considered 5
• All children with confirmed hypertension should have renal ultrasonography 5

Middle-Aged Adults (30-65 years)

• Primary aldosteronism is a common cause 5
• Sleep apnea prevalence increases 6
• Pheochromocytoma and Cushing's syndrome should be considered with appropriate symptoms 4

Older Adults (>65 years)

• Atherosclerotic renal artery stenosis becomes more common 4, 5
• Renal failure and thyroid disorders increase in prevalence 4

Common Pitfalls to Avoid

• Failing to recognize medication-induced hypertension
• Not considering secondary hypertension in resistant cases
• Overlooking sleep apnea as a common secondary cause 6
• Inadequate follow-up after initiating ACE inhibitors in patients with possible renal artery stenosis 4
• Premature exclusion of secondary causes in patients with longstanding hypertension

Referral Considerations

Consider referring patients with suspected secondary hypertension to specialist centers with appropriate expertise and resources, particularly for complex cases requiring advanced diagnostic procedures 1.

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