UWorld Internal Medicine Practice Test

In a young woman exhibiting signs of adrenal insufficiency, such as hyperpigmentation and low cortisol levels following ACTH stimulation, the expected electrolyte abnormality is indeed characterized by low sodium (Na) and high potassium (K) levels.

Adrenal insufficiency can arise from conditions like Addison's disease, where there is inadequate production of glucocorticoids and mineralocorticoids due to adrenal gland damage. The adrenal cortex produces aldosterone, a hormone that plays a key role in regulating sodium and potassium levels, among other functions. In the absence of adequate aldosterone secretion, sodium reabsorption in the kidneys is impaired, leading to hyponatremia (low sodium levels). Concurrently, because sodium is not reabsorbed efficiently, potassium, which is usually secreted in exchange with sodium, remains elevated, causing hyperkalemia (high potassium levels).

Chloride levels can vary but are often influenced by changes in sodium levels; hence, high levels of potassium and low levels of sodium leading to metabolic disturbances can also result in altered chloride concentrations. However, the most direct and significant findings in adrenal insufficiency are the low sodium and high potassium levels.

This physiological basis elucidates why the combination of low sodium and high