What causes polyuria in diabetes?

What causes polyuria in diabetes?

• A. Dehydration from vomiting
• B. Increased ADH
• C. Diuretic use
• D. Osmotic diuresis due to high glucose levels leading to water loss

Answer: (D)

In diabetes, polyuria comes from osmotic diuresis caused by high blood glucose. When plasma glucose is elevated beyond the kidney’s reabsorptive capacity, glucose spills into the urine (glucosuria). This glucose in the tubular lumen pulls water with it by osmosis, increasing urine volume. The result is persistent, large-volume urination despite normal or even high fluid intake. This mechanism explains why polyuria occurs specifically in the setting of hyperglycemia. The other options don’t fit this diabetes-specific process: vomiting causes dehydration but not osmotic water loss via glucosuria; altering ADH would change water reabsorption in the opposite direction and wouldn’t produce the glucosuria-driven diuresis; diuretic use increases urine through pharmacologic action, not through the glucose-driven osmotic effect seen in diabetes.

In diabetes, polyuria comes from osmotic diuresis caused by high blood glucose. When plasma glucose is elevated beyond the kidney’s reabsorptive capacity, glucose spills into the urine (glucosuria). This glucose in the tubular lumen pulls water with it by osmosis, increasing urine volume. The result is persistent, large-volume urination despite normal or even high fluid intake. This mechanism explains why polyuria occurs specifically in the setting of hyperglycemia. The other options don’t fit this diabetes-specific process: vomiting causes dehydration but not osmotic water loss via glucosuria; altering ADH would change water reabsorption in the opposite direction and wouldn’t produce the glucosuria-driven diuresis; diuretic use increases urine through pharmacologic action, not through the glucose-driven osmotic effect seen in diabetes.