American Board of Internal Medicine (ABIM) Certification Practice Exam

What type of renal tubular acidosis is characterized by urine loss of bicarbonate, phosphaturia, glucosuria, and aminoaciduria?

1. Type 1 (Distal) renal tubular acidosis

2. Type 2 (Proximal) renal tubular acidosis

3. Type 4 renal tubular acidosis

4. Chronic kidney disease

The correct answer is: Type 2 (Proximal) renal tubular acidosis

The condition described in the question aligns with Type 2 (Proximal) renal tubular acidosis. This type is characterized by the impaired ability of the proximal tubules of the kidney to reabsorb bicarbonate. In cases of proximal RTA, patients can present with an elevated bicarbonate concentration in the urine, leading to a loss of bicarbonate that contributes to acidosis. Moreover, this form of renal tubular acidosis can also manifest with phosphaturia, glucosuria, and aminoaciduria due to the proximal tubule's role in reabsorbing not only bicarbonate but also glucose, phosphate, and amino acids. In proximal RTA, because the tubules are not functioning properly, there is a spilling of these substances into urine, which explains the glucosuria and aminoaciduria observed in patients. The other types of renal tubular acidosis do not present with the same combination of features. For instance, Type 1 (Distal) renal tubular acidosis typically involves an inability to excrete hydrogen ions, leading to a different presentation of acidosis without the characteristic bicarbonate loss and associated conditions seen in the proximal type. Type 4 renal tubular acidosis is often associated with hyperkalemia and does not specifically