In SIADH, which finding regarding urine sodium is typical?

In SIADH, which finding regarding urine sodium is typical?

• A. Low urine sodium
• B. Mildly decreased urine sodium
• C. Normal urine sodium
• D. Elevated urine sodium

Answer: (D)

In SIADH, the problem is excess ADH causing water retention, which dilutes the serum sodium while leaving the patient euvolemic. To maintain this euvolemic state, the kidneys excrete sodium, so urine becomes rich in sodium. That natriuresis is why urine sodium is elevated. In practice, urine sodium is typically greater than 20–30 mEq/L (often higher). This elevated urine sodium aligns with the hyponatremia seen in SIADH, unlike low or normal urine sodium that would suggest hypovolemia or other different processes.

In SIADH, the problem is excess ADH causing water retention, which dilutes the serum sodium while leaving the patient euvolemic. To maintain this euvolemic state, the kidneys excrete sodium, so urine becomes rich in sodium. That natriuresis is why urine sodium is elevated. In practice, urine sodium is typically greater than 20–30 mEq/L (often higher). This elevated urine sodium aligns with the hyponatremia seen in SIADH, unlike low or normal urine sodium that would suggest hypovolemia or other different processes.