Fluid overload and SIADH cause which change in urine specific gravity?

Fluid overload and SIADH cause which change in urine specific gravity?

• A. Decreased
• B. Increased
• C. Normal
• D. Variable

Answer: (B)

The key idea is that these conditions drive the kidneys to hold onto water, not lose it. In SIADH, antidiuretic hormone is secreted inappropriately, so water reabsorption in the collecting ducts increases. That makes the urine more concentrated while the blood becomes relatively diluted, and the urine’s density rises. A concentrated urine has more solutes per liter, which shows up as an increased urine specific gravity (often higher than normal, with urine osmolality well above the dilute range). Even in fluid overload, where you might expect the body to dilute the urine, the excess ADH keeps reabsorbing water, leading to a consistently higher specific gravity. In short, the urinary filtrate becomes more concentrated, so the specific gravity increases.

The key idea is that these conditions drive the kidneys to hold onto water, not lose it. In SIADH, antidiuretic hormone is secreted inappropriately, so water reabsorption in the collecting ducts increases. That makes the urine more concentrated while the blood becomes relatively diluted, and the urine’s density rises. A concentrated urine has more solutes per liter, which shows up as an increased urine specific gravity (often higher than normal, with urine osmolality well above the dilute range). Even in fluid overload, where you might expect the body to dilute the urine, the excess ADH keeps reabsorbing water, leading to a consistently higher specific gravity. In short, the urinary filtrate becomes more concentrated, so the specific gravity increases.