## Secondary Hypertension — Epidemiology **Key Point:** Chronic kidney disease (CKD) is the most common identifiable cause of secondary hypertension in the adult population, accounting for approximately 3–5% of all hypertension cases. ### Mechanism in CKD 1. **Sodium retention** — reduced GFR → impaired sodium excretion → volume expansion 2. **Renin-angiotensin-aldosterone system (RAAS) activation** — renal hypoperfusion triggers renin release 3. **Sympathetic nervous system overactivity** — uremic toxins and fluid overload 4. **Endothelial dysfunction** — reduced nitric oxide bioavailability ### Relative Frequency of Secondary Causes | Cause | Prevalence (%) | Key Feature | |-------|----------------|-------------| | Chronic kidney disease | 3–5 | Most common; progressive decline in GFR | | Primary hyperaldosteronism | 1–2 | Hypokalemia, metabolic alkalosis | | Obstructive sleep apnea | 1–2 | Nocturnal hypoxia, daytime somnolence | | Pheochromocytoma | <0.1 | Episodic symptoms, elevated catecholamines | | Coarctation of aorta | <0.1 | Young patient, upper limb hypertension | | Cushing syndrome | <0.1 | Central obesity, striae, proximal weakness | **High-Yield:** Remember that ~90–95% of hypertension is essential (primary); secondary causes are identified in only 5–10% of hypertensive patients. Of those with secondary hypertension, CKD is the single most common etiology. **Clinical Pearl:** In a patient with newly diagnosed hypertension and a known history of renal disease, always measure serum creatinine and eGFR early — CKD-related hypertension often requires dual RAAS blockade (ACE inhibitor + aldosterone antagonist) in addition to other agents.
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