Osmotic diuresis in diabetes occurs because which of the following?

• A. Glucose in the urine pulls water with it, increasing urine output
• B. Water retention due to hormonal changes
• C. Ketone bodies attract water into the urine
• D. Decreased glomerular filtration

Answer: (A)

Osmotic diuresis happens when an osmotically active substance stays in the urine and pulls water with it. In diabetes, blood glucose becomes very high, and the kidney can't reabsorb all of it beyond a certain limit. The excess glucose spills into the urine and remains in the tubular fluid, so water is drawn into the urine by osmosis. This increases urine volume (polyuria) and can lead to dehydration and thirst.

The other ideas don’t explain the big rise in urine output seen in this context: hormonal water retention would reduce, not increase, urine; ketone bodies can have osmotic effects in some diabetic states but aren’t the primary driver of osmotic diuresis in typical diabetes; and a lower glomerular filtration rate would generally decrease urine formation rather than cause the glucose-driven water loss described here.