USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What is an expected effect of mineralocorticoid excess on potassium levels?

1. Hypokalemia

2. Hyperkalemia

3. Normal potassium levels

4. Wild fluctuations in potassium levels

The correct answer is: Hypokalemia

Mineralocorticoids, such as aldosterone, play a crucial role in electrolyte balance, particularly in the regulation of sodium and potassium levels. When there is an excess of mineralocorticoids, one of the primary physiological actions is the increased reabsorption of sodium in the renal tubules, which is usually accompanied by the secretion of potassium. This process leads to a significant reduction in serum potassium levels, resulting in hypokalemia. This effect is particularly evident in conditions such as hyperaldosteronism, where the heightened levels of aldosterone cause the kidneys to excrete more potassium while retaining sodium. Thus, the expected outcome of mineralocorticoid excess is a decrease in potassium levels, leading to hypokalemia.