Diabetes insipidus laboratory finding most consistent with the condition?

Diabetes insipidus laboratory finding most consistent with the condition?

• A. Increased urine osmolality
• B. Increased serum osmolality
• C. Decreased serum osmolality
• D. Decreased urine output

Answer: (B)

In diabetes insipidus, there is a deficiency or resistance to antidiuretic hormone, so the kidneys cannot concentrate the urine. This leads to large volumes of very dilute urine (low urine osmolality and low urine specific gravity) and loss of free water. As water is lost from the body, the remaining serum becomes more concentrated, raising the serum osmolality. So the most consistent lab finding is increased serum osmolality. Note that urine output is typically increased (polyuria) and urine osmolality would be decreased, not increased, in DI. Decreased serum osmolality would suggest overhydration or other conditions, not DI.

In diabetes insipidus, there is a deficiency or resistance to antidiuretic hormone, so the kidneys cannot concentrate the urine. This leads to large volumes of very dilute urine (low urine osmolality and low urine specific gravity) and loss of free water. As water is lost from the body, the remaining serum becomes more concentrated, raising the serum osmolality. So the most consistent lab finding is increased serum osmolality.

Note that urine output is typically increased (polyuria) and urine osmolality would be decreased, not increased, in DI. Decreased serum osmolality would suggest overhydration or other conditions, not DI.