Primary Hypertension vs Secondary Hypertension
Primary hypertension (essential hypertension) has no identifiable cause, while secondary hypertension is caused by an underlying medical condition that can potentially be treated or cured. 1
Key Differences
Primary Hypertension
- Accounts for 90-95% of all hypertension cases
- No specific identifiable cause
- Develops gradually over years
- Influenced by genetic and lifestyle factors
- Treatment focuses on medication and lifestyle modifications
Secondary Hypertension
- Accounts for 5-10% of all hypertension cases in adults 1, 2
- Has a specific identifiable and potentially reversible underlying cause 2
- Often presents with more severe or resistant hypertension
- May have sudden onset or acute rise from previously stable readings
- Treatment targets the underlying condition in addition to blood pressure control
When to Suspect Secondary Hypertension
Secondary hypertension should be considered in patients with:
- Severe or resistant hypertension
- Age of onset younger than 30 years (especially before puberty)
- Malignant or accelerated hypertension
- Acute rise in blood pressure from previously stable readings 2
- Increase in serum creatinine ≥50% within one week of starting ACE inhibitors or ARBs
- Severe hypertension with unilateral smaller kidney or >1.5 cm difference in kidney size
- Recurrent flash pulmonary edema 2
Common Causes of Secondary Hypertension
| Suspected Cause | Recommended Screening Test | Key Clinical Features |
|---|---|---|
| Primary aldosteronism | Aldosterone-to-renin ratio | Hypokalemia, metabolic alkalosis |
| Renovascular hypertension | Renal Doppler ultrasound, CT/MR angiography | Abdominal bruit, deteriorating renal function with ACEi/ARBs |
| Pheochromocytoma | 24h urinary/plasma metanephrines | Episodic headaches, sweating, palpitations |
| Obstructive sleep apnea | Overnight polysomnography | Snoring, daytime sleepiness, obesity |
| Renal parenchymal disease | Renal ultrasound, urinalysis, eGFR | Abnormal urinalysis, elevated creatinine |
| Cushing's syndrome | 24h urinary free cortisol | Central obesity, moon facies, striae |
| Thyroid disease | TSH | Tachycardia or bradycardia, weight changes |
| Hyperparathyroidism | PTH, calcium, phosphate | Hypercalcemia, bone pain |
| Coarctation of aorta | Echocardiogram, CT angiogram | BP differential between arms and legs, delayed femoral pulses [1] |
Age-Related Considerations
- Children: Most common causes are renal parenchymal disease and coarctation of the aorta 2
- Young adults: Consider genetic causes, fibromuscular dysplasia, and endocrine disorders
- Adults 65+ years: Atherosclerotic renal artery stenosis, renal failure, and hypothyroidism are common causes 2
Management Approach
- Confirm hypertension with multiple readings on different occasions
- Screen for secondary causes when clinical suspicion exists
- Treat the underlying cause when identified:
- Unilateral adrenalectomy for unilateral primary aldosteronism
- Renal angioplasty for fibromuscular dysplasia
- CPAP therapy for obstructive sleep apnea
- Surgical removal after adequate alpha-blockade for pheochromocytoma 1
- Continue antihypertensive therapy as needed, even after addressing the underlying cause
Common Pitfalls to Avoid
- Missing secondary causes in patients with resistant hypertension (requiring ≥3 medications)
- Initiating beta-blockers before alpha-blockers in suspected pheochromocytoma (can precipitate hypertensive crisis)
- Failing to consider medication-induced hypertension (NSAIDs, oral contraceptives, decongestants, etc.)
- Not performing ambulatory BP monitoring to rule out white-coat hypertension before extensive workup 1
- Overlooking the possibility of combined pathologies, such as hypertension and diabetes together worsening target organ damage 1
Secondary hypertension is often underrecognized but identifying and treating the underlying cause can lead to significant improvements in blood pressure control and potentially cure the hypertension in some cases 3, 4.