Question

A 30-year-old man with acromegaly undergoes the transsphenoidal resection of a pituitary adenoma. On postoperative day one, the patient develops a brisk diuresis. Which of the following laboratory measurements MOST supports the diagnosis of diabetes insipidus? 1) Serum sodium 145 meq/L 2) Serum sodium 135 meq/L 3) Urine osmolarity of 300 mOsm/L 4) Urine osmolarity of 450 mOsm/L

Answer 1

The most indicative laboratory measurement for diagnosing diabetes insipidus in this instance would be urine osmolarity of 300 mOsm/L. This suggests dilute urine due to the kidneys' reduced capacity to recover water owing to a lack of ADH, which is a hallmark of diabetes insipidus.

Step-by-step explanation:

The laboratory measurement that would most support a diagnoses of diabetes insipidus in a patient who develops a brisk diuresis after transsphenoidal resection of a pituitary adenoma would be 3) Urine osmolarity of 300 mOsm/L. Diabetes insipidus is characterized by a chronic underproduction of ADH, diminishing the kidneys' capacity to reabsorb water which results in decreased urine osmolarity.

Without sufficient ADH, urine is not concentrated in the kidneys and osmolarity, or concentration of solutes in urine, would be low. In this scenario, a urine osmolarity of 300 mOsm/L represents dilute urine, typically seen in patients with diabetes insipidus as water is not being reabsorbed effectively by the kidneys.

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