In a patient with a pituitary disorder being treated for fluid balance, which urine finding would indicate improved concentrating ability?

• A. Urine output of 3 liters per day
• B. Urine specific gravity less than 1.025
• C. Urine osmolality of 80 mOsm/kg
• D. Urine pH of 9

Answer: (B)

Concentrating urine depends on ADH acting on the kidneys to reabsorb water. When fluid balance is being corrected after a pituitary disorder, improvement means the kidneys are able to produce more concentrated urine, not dilute urine.

The clearest signs of that improvement are higher urine osmolality and higher urine specific gravity, since both rise as urine becomes more concentrated. A high volume of urine output suggests the opposite—ongoing polyuria and poor concentrating ability. Very low osmolality indicates dilute urine, which again does not reflect improvement. Urine pH is not a measure of concentrating ability.

So, true improvement would be shown by an increase in osmolality and/or an increase in specific gravity toward the concentrated range, reflecting restored ADH effect and water reabsorption.