What bloodwork and tests are recommended after switching to amlodipine (calcium channel blocker) to evaluate for secondary causes of Hypertension (HTN)?

Bloodwork and Testing for Secondary Hypertension After Switching to Amlodipine

After switching to amlodipine, obtain a comprehensive metabolic panel (including serum creatinine with eGFR, sodium, potassium, calcium), fasting glucose or HbA1c, lipid profile, TSH, urinalysis with urinary albumin-to-creatinine ratio, complete blood count, and ECG as your baseline workup for secondary causes of hypertension. 1

Basic Laboratory Testing (Required for All Patients)

The following tests should be obtained to screen for secondary hypertension and establish baseline values:

• Comprehensive metabolic panel including serum creatinine with estimated GFR, sodium, potassium, and calcium 1
• Fasting blood glucose or HbA1c 1
• Complete blood count 1
• Lipid profile 1
• Thyroid-stimulating hormone (TSH) to detect hypo- or hyperthyroidism as remediable causes 1
• Urinalysis for blood and protein 1
• Urinary albumin-to-creatinine ratio 1
• 12-lead electrocardiogram to assess for left ventricular hypertrophy 1, 2

Targeted Testing Based on Clinical Suspicion

If you suspect specific secondary causes based on clinical features, age, or severity of hypertension, proceed with these additional tests: 1

Primary Aldosteronism

• Aldosterone-to-renin ratio (ARR) is the screening test of choice 1
• Important caveat: Amlodipine (a dihydropyridine calcium channel blocker) can cause a minimal decrease in aldosterone and minimal increase in renin, potentially leading to false-negative results 1
• Review prior potassium levels, as hypokalaemia increases likelihood of primary aldosteronism 1

Renovascular Hypertension

• Renal Doppler ultrasound as initial imaging 1
• CT angiography or MRI angiography of renal arteries for definitive evaluation 1
• Consider especially in patients <40 years (fibromuscular dysplasia) or >60 years with acute BP changes or flash pulmonary edema (atherosclerotic disease) 1

Pheochromocytoma/Paraganglioma

• 24-hour urinary metanephrines and normetanephrines and/or plasma metanephrines 1

Obstructive Sleep Apnea

• Overnight ambulatory polysomnography if patient has resistant hypertension, non-dipping BP pattern, obesity, or suggestive symptoms 1
• Up to 60% of resistant hypertension patients have obstructive sleep apnea 1

Cushing's Syndrome

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

Hyperparathyroidism

• Parathyroid hormone (PTH) 1
• Calcium and phosphate 1

Coarctation of the Aorta

• Echocardiogram 1
• Aortic CT angiography 1
• Measure thigh BP in patients ≤30 years; if lower than arm pressures, suspect coarctation 1

Monitoring Considerations Specific to Amlodipine

• Monitor serum creatinine and eGFR closely, as amlodipine may cause slight elevations in some patients with renal impairment (11.4% in one study), though it generally does not worsen renal function 3, 4
• Recheck electrolytes (sodium and potassium) during titration, though amlodipine does not typically cause significant electrolyte disturbances 5
• Amlodipine may improve glycemic control compared to thiazides, so reassess glucose parameters if switching from a diuretic 6

Clinical Pitfalls to Avoid

• Do not perform aldosterone-to-renin ratio testing while on short-acting dihydropyridine calcium channel blockers, as they can cause false-negative results 1
• Young age (<30 years) is a critical red flag for secondary hypertension and mandates thorough evaluation 2
• Resistant hypertension (BP uncontrolled on 3+ medications) should trigger aggressive screening for secondary causes, particularly obstructive sleep apnea and primary aldosteronism 1
• Do not delay testing if clinical features suggest secondary hypertension, even if BP improves on amlodipine 1, 2