Prior to giving treatment
Urine
Urinalysis
Urine electrolytes (Urine sodium)
Urine urea
urine uric acid
urine osmolality
urine creatinine
Serum
Chemistry including Ca/Mg/Phos
Serum osmolality
Uric acid
TSH
Cortisol
Urinalysis
Urine electrolytes (Urine sodium)
Urine urea
urine uric acid
urine osmolality
urine creatinine
Chemistry including Ca/Mg/Phos
Serum osmolality
Uric acid
TSH
Cortisol
Defined as osmolarity > 295mmol/L with the following causes:
Sodium decreases by 2.4mEq/L for each 100mg/dL increase in glucose over 100mg/dL
Defined as osmolarity > 275-295mmol/L.  Often referred to as pseudo<unk>  because the elevated lipids or proteins interfere with the laboratory sodium reading.  The following are common causes:
Defined as an osmolarity < 275 mmol/L and categorized as hypovolemic, hypervolemic or euvolemic
Hyponatremia
Thiazide diuretic use
Hypernatremia
Na-wasting nephropathy 
Hypercapnia
Osmotic diuresis 
Hypermagnesemia
Aldosterone deficiency