American Board of Internal Medicine (ABIM) Certification Practice Exam

What condition mimics the effect of a loop diuretic and is characterized by increased urine sodium, potassium, and chloride excretion?

1. Bartter syndrome

2. Fanconi syndrome

3. Oncogenic osteomalacia

4. Acute tubular necrosis

The correct answer is: Bartter syndrome

Bartter syndrome is characterized by a set of congenital disorders that lead to impaired reabsorption of sodium, potassium, and chloride in the loop of Henle, which is a key part of the renal tubule system. This impairment results in increased excretion of these electrolytes, simulating the effect of loop diuretics, which also promote the loss of these ions through the urine. Individuals with Bartter syndrome typically present with metabolic alkalosis, hypokalemia, and an increased renal excretion of sodium, potassium, and chloride. This syndrome can manifest in childhood or early adulthood and is often identified by its distinct biochemistry, including high urine sodium levels and low blood pressure due to volume contraction. The condition highlights the kidneys' role in electrolyte and fluid balance and can help illustrate pathophysiology related to loop diuretics, reinforcing an understanding of kidney function in both health and disease. In contrast, Fanconi syndrome is characterized by a generalized loss of tubular reabsorption, leading primarily to phosphate and bicarbonate wasting, but not specifically mimicking loop diuretics. Oncogenic osteomalacia involves renal phosphate wasting but is associated with increased levels of fibroblast growth factor 23 (FGF23). Acute tubular necrosis