American Board of Surgery Qualifying Exam (ABS QE) Practice Test

What laboratory findings are typically present in 21-hydroxylase deficiency?

1. Hypernatremia, hyperkalemia

2. Hyponatremia, hyperkalemia

3. Hypokalemia, elevated renin

4. Hypertension, low aldosterone

The correct answer is: Hyponatremia, hyperkalemia

In 21-hydroxylase deficiency, a condition commonly associated with congenital adrenal hyperplasia, there is a significant disruption in the adrenal steroid synthesis pathway. The enzyme 21-hydroxylase is crucial for the conversion of 17-hydroxyprogesterone to 11-deoxycortisol and for converting progesterone to 11-deoxycorticosterone. When this enzyme is deficient, the pathway is blocked, leading to inadequate production of cortisol and aldosterone. Due to low aldosterone levels, the body struggles to retain sodium, resulting in hyponatremia (low sodium levels). Simultaneously, there is an accumulation of steroid precursors that can lead to increased production of adrenal androgens, contributing to the clinical manifestations of the condition. The deficiency of aldosterone, which normally promotes potassium excretion, results in hyperkalemia (high potassium levels) as excess potassium remains in the bloodstream. Thus, the combination of hyponatremia and hyperkalemia is characteristic of 21-hydroxylase deficiency, making this answer the most accurate regarding the laboratory findings typically present in this condition.