Recurrent calcium oxalate/phosphate stones --> The patient is instructed to follow a low sodium diet + drink 3-4 liters of water per day + avoid vitamin C drinks.
Order the following labs:
24 hour urine studies including collection of sodium, citric acid, oxalate,
calcium, and uric acid.
=> If uric acid in urine is high may benefit from allopurinol.
In addition, the intact-PTH level is high with a normal vitamin D 25 level. As his GFR is normal along with the history of recurrent nephrolithiasis, primary hyperparathyroidism is quite possible.