American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the urine sodium cutoff to determine if sodium levels are elevated or decreased?

1. 20

2. 30

3. 10

4. 40

The correct answer is: 20

The urine sodium concentration is an important parameter used to assess a patient’s sodium status and help differentiate between various causes of electrolyte imbalances such as hyponatremia or hypernatremia. A urine sodium level of 20 mEq/L is commonly accepted as a cutoff in clinical practice. When evaluating conditions like hyponatremia, if the urine sodium level is less than 20 mEq/L, it typically suggests that the kidneys are conserving sodium due to conditions like hypovolemia. Conversely, a urine sodium level greater than 20 mEq/L often indicates that the kidneys are excreting sodium freely, which could be a response to conditions such as euvolemia or hypervolemia, or due to renal causes. Therefore, the urine sodium cutoff of 20 mEq/L provides a practical guideline for clinicians to evaluate patients with altered sodium levels, helping them determine the underlying cause and direct appropriate management strategies.