Measurement	Calculator	Equations and comments
Sodium correction for hyperglycemia	https://www.mdcalc.com/sodium-correction-for-hyperglycemia	Measured sodium + 0.016 × (serum glucose − 100) Measured sodium + 0.024 × (serum glucose − 100)*
Serum osmolality	https://www.mdcalc.com/serum-osmolality-osmolarity	Serum osmolality = (sodium × 2) + (glucose ÷ 18) + (blood urea nitrogen ÷ 2.8) Normal osmolality = 280 to 295 mOsm per kg In patients with hyperglycemia, uncorrected sodium should be used to calculate osmolality
Sodium deficit	https://www.mdcalc.com/sodium-deficit-in-hyponatremia	Sodium deficit = total body water % × body weight (kg) × (desired sodium − actual sodium) For total body water %, use 0.6 for men and 0.5 for women
Infusion rate of sodium	https://www.mdcalc.com/sodium-correction-rate-hyponatremia-hypernatremia	Serum sodium correction should not proceed faster than 0.5 mEq per L per hour for the first 24 to 48 hours; however, in patients with severe symptoms, a rate of 1.0 to 2.0 mEq per L per hour is acceptable (these situations typically require use of 3% saline) The goal is to increase the serum sodium concentration by 6 to 8 mEq per L, not to exceed 10 to 12 mEq per L in the first 24 hours and 18 mEq per L in the first 48 hours
Free water deficit in hypernatremia	https://www.mdcalc.com/free-water-deficit-in-hypernatremia	0.6 × body weight (kg) × [(serum sodium ÷ 140) − 1] Results of this formula are in liters Administer the total volume as free water over 24 hours using oral or enteral free water (preferred), or hypotonic fluids such as dextrose 5% in water
Fractional excretion of uric acid	https://www.scymed.com/en/smnxps/pspdj228.htm	Fractional excretion of uric acid = (urinary uric acid × serum creatinine) ÷ (serum uric acid × urine creatinine) Less than 0.1 suggests prerenal causes, while > 0.1 indicates syndrome of inappropriate antidiuretic hormone secretion or renal etiologies