What is the most common cause of secondary hypertension?

The most common cause of secondary hypertension is chronic kidney disease. This condition leads to hypertension primarily due to the kidneys' crucial role in regulating blood volume and systemic vascular resistance. When kidney function is impaired, either due to chronic damage or disease processes, the kidneys may not effectively regulate fluid balance and electrolyte levels, leading to increased blood volume and consequently higher blood pressure.

Additionally, the kidneys can activate the renin-angiotensin-aldosterone system in response to decreased perfusion or damage, further exacerbating hypertension. Chronic kidney disease not only alters the anatomy and function of the kidneys but also frequently leads to a failure to excrete sodium, which can contribute to fluid retention and elevated blood pressure.

In contrast, obstructive sleep apnea, while a significant contributor to secondary hypertension, is less prevalent than chronic kidney disease. Other options like Cushing's syndrome and hyperthyroidism can certainly lead to hypertension through different mechanisms, such as increased cortisol or thyroid hormone levels, respectively. However, chronic kidney disease remains the most common etiology in the context of secondary hypertension due to its widespread prevalence and standardized progression in various populations.