Admit if symptomatic or if Na <125mEq/L
Manage severely symptomatic patients in "an environment where close biochemical and clinical monitoring can be provided" (e.g. ICU)
Hyponatremia
Thiazide diuretic use
Hypernatremia
Na-wasting nephropathy 
Hypercapnia
Osmotic diuresis 
Hypermagnesemia
Aldosterone deficiency