What is the most common cause of secondary hypertension?

Secondary hypertension is caused by an identifiable underlying condition, and several factors can contribute to its onset. Chronic kidney disease, Cushing's syndrome, and obstructive sleep apnea are indeed among the most common causes.

Chronic kidney disease leads to hypertension as the kidneys play a crucial role in regulating blood pressure through fluid and electrolyte balance, as well as the production of hormones that affect vascular resistance. As the kidneys become impaired, these regulatory systems are disrupted, often resulting in elevated blood pressure.

Cushing's syndrome, characterized by excessive levels of cortisol, can also cause hypertension primarily through increased blood volume and vascular sensitivity to catecholamines, leading to elevated blood pressure.

Obstructive sleep apnea is another significant contributor to secondary hypertension, as it causes intermittent hypoxia, leading to sympathetic nervous system activation and increased systemic vascular resistance.

Acknowledging that each of these conditions can cause secondary hypertension, the correct answer indicates the understanding that all of these conditions are relevant causes, reflecting the multifactorial nature of secondary hypertension.