What tests are used to diagnose secondary hypertension?

Testing for Secondary Hypertension

Secondary hypertension testing should begin with basic screening followed by targeted investigations based on clinical clues, with referral to specialist centers for complex cases. 1

When to Screen for Secondary Hypertension

Secondary hypertension should be considered in patients with:

• Early onset hypertension (<30 years of age), especially without typical risk factors
• Resistant hypertension (BP >140/90 mmHg despite three medications including a diuretic)
• Sudden deterioration in previously controlled BP
• Hypertensive urgency or emergency
• Strong clinical clues suggesting a secondary cause 1

Initial Screening Process

Step 1: Basic Screening for All Suspected Cases

• Thorough history and physical examination focusing on symptoms and signs of secondary causes
• Basic blood biochemistry:
  • Serum sodium and potassium (hypokalemia suggests aldosteronism)
  • Estimated glomerular filtration rate (eGFR)
  • Thyroid stimulating hormone (TSH)
• Dipstick urinalysis (for blood and protein) 1

Step 2: Rule Out Pseudoresistant Hypertension

Before proceeding with extensive workup, exclude:

• Poor BP measurement technique
• White coat effect
• Medication nonadherence
• Suboptimal antihypertensive therapy
• Substance/drug-induced hypertension 1

Targeted Testing Based on Clinical Suspicion

For Primary Aldosteronism

• Aldosterone-to-renin ratio (ARR) as initial test
• Review prior potassium levels (hypocalemia increases likelihood)
• Consider medication interference with test results (see below) 1

For Renovascular Hypertension

• Renal Doppler ultrasound
• Abdominal CT angiogram or MRI angiogram (depending on renal function)
• Consider in patients with acute decline in renal function after starting ACE inhibitors/ARBs 1

For Pheochromocytoma/Paraganglioma

• 24-hour urinary and/or plasma metanephrine and normetanephrine 1

For Obstructive Sleep Apnea

• Overnight ambulatory polysomnography
• Consider in patients with resistant hypertension, obesity, or non-dipping BP pattern
• Validated questionnaires may help identify high-risk patients 1

For Renal Parenchymal Disease

• Plasma creatinine, sodium, potassium
• eGFR
• Urinary albumin-to-creatinine ratio
• Renal ultrasound 1

For Cushing's Syndrome

• 24-hour urinary free cortisol
• Low-dose dexamethasone suppression test 1

For Thyroid Disease

• TSH measurement 1

For Hyperparathyroidism

• Parathyroid hormone
• Calcium and phosphate levels 1

For Coarctation of the Aorta

• Echocardiogram
• Aortic CT angiogram 1

Important Considerations for Testing

Medication Interference with Test Results

Certain medications can affect aldosterone and renin levels, potentially causing false results:

• Beta-blockers: Decrease renin, may cause false positive ARR
• ACE inhibitors/ARBs: Increase renin, may cause false negative ARR
• Diuretics: Affect both aldosterone and renin levels
• NSAIDs: Decrease renin, may cause false positive ARR 1

Pitfalls to Avoid

• Failing to exclude pseudoresistant hypertension before extensive workup
• Not considering medication effects on diagnostic test results
• Overlooking sleep apnea in obese patients with resistant hypertension
• Missing renovascular disease in young women (fibromuscular dysplasia) or older adults with atherosclerosis
• Not testing for primary aldosteronism in patients with hypokalemia 1

Referral Recommendations

Consider referring patients with suspected secondary hypertension to specialist centers with appropriate expertise and resources for further investigation and management, particularly for complex cases or when initial testing suggests a secondary cause 1.