A 74-year-old man is brought to the hospital because of urinary retention. His past medical history includes hypertension, and benign prostatic hypertrophy. A Foley catheter is inserted to relieve the obstruction, and 1500 cc of urine is emptied from his bladder. Over the next few hours, he has 200cc/h of urine output. Which of the following urine electrolyte values is most likely in keeping with his diagnosis of post obstructive diuresis?

The urine contains large amounts of potassium, magnesium, and sodium. The large volume is often appropriate from the preexisting volume expansion that occurs during the obstruction and poor renal output. Careful attention to fluid and electrolytes is important after the obstruction is relieved, to prevent hypokalemia, hypomagnesemia, hyponatremia or hypernatremia, and volume depletion. The urine osmolality is low since ADH is decreased from the volume expansion prior to the insertion of the catheter and later if the diuresis continues once the patient is euvolemic it is indicative of tubular dysfunction from the prolonged post-renal obstruction.