A 40-year-old woman presents with progressive fatigue, generalized weakness, weight loss, and hyperpigmentation of her skin. Laboratory tests reveal hyponatremia, hyperkalemia, and hypoglycemia. What is the most appropriate initial diagnostic test?

The correct answer to the question "A 40-year-old woman presents with progressive fatigue, generalized weakness, weight loss, and hyperpigmentation of her skin. Laboratory tests reveal hyponatremia, hyperkalemia, and hypoglycemia. What is the most appropriate initial diagnostic test?" is Option B: ACTH stimulation test.

The other options — A) Serum cortisol level at 8 AM, C) 24-hour urine free cortisol, D) Thyroid stimulating hormone (TSH) — are incorrect for this USMLE Exam Prep question. As explained above: The patient's symptoms and electrolyte abnormalities are classic for primary adrenal insufficiency (Addison's disease). The most appropriate initial diagnostic test is the ACTH stimulation test, whic…