What abnormality is consistent with Conn's syndrome?

Conn's syndrome, also known as primary hyperaldosteronism, is characterized by the overproduction of aldosterone from the adrenal glands, typically due to an adrenal adenoma or hyperplasia. This condition results in several physiological effects due to excessive aldosterone.

The correct answer, decreased plasma renin activity, is a critical hallmark of Conn's syndrome. In this disorder, the excess aldosterone leads to sodium retention and increased blood volume, which in turn suppresses the renin-angiotensin-aldosterone system (RAAS). Since aldosterone works to increase sodium reabsorption and blood pressure, the body's feedback mechanism will decrease renin production in an attempt to lower excessively high aldosterone levels. Therefore, patients with Conn's syndrome typically display low plasma renin activity as a manifestation of this negative feedback loop.

In contrast, elevated plasma renin activity would indicate an activation of the RAAS, which is not consistent with Conn's syndrome since the condition involves excessive levels of aldosterone. Hyperkalemia, or elevated potassium levels, is generally associated with conditions of aldosterone deficiency (e.g., adrenal insufficiency) and is typically not seen in Conn's syndrome, where aldosterone promotes potassium excretion. Low levels of aldosterone also