Measurement	Equation
Corrected sodium	Measured sodium + 0.024 × (serum glucose − 100)*
		or
	Measured sodium + 0.016 × (serum glucose − 100)
	Normal = 135 to 145 mEq per L
	Online calculators available at http://www.mdcalc.com/sodium-correction-for-hyperglycemia and http://www.medcalc.com/correctna.html
Fractional excretion of sodium	([Plasma creatinine × urinary sodium] / [plasma sodium × urinary creatinine]) × 100
	Prerenal < 1%, intrinsic > 1%, and postrenal > 4%
	Online calculators available at http://www.mdcalc.com/fractional-excretion-of-sodium-fena and http://www.medcalc.com/fena.html
Infusion rate of sodium	Online calculators for the rate of infusion and the concentration of sodium required are available at http://www.mdcalc.com/sodium-correction-rate-in-hyponatremia, http://www.medcalc.com/sodium.html, and http://www.nephromatic.com/sodium_correction.php
	Serum sodium correction should generally not proceed faster than 0.5 mEq per L per hour for the first 24 to 48 hours; however, in severely symptomatic patients, the rate can be 1.0 to 2.0 mEq per L per hour; these situations typically require use of 3% saline
	The goal is to raise the serum sodium level not to exceed 10 to 12 mEq per L in the first 24 hours and 18 mEq per L in the first 48 hours
	Isotonic saline contains 154 mEq of sodium per L, and 3% saline contains 513 mEq of sodium per L
Serum osmolality	(Sodium × 2) + (glucose / 18) + (blood urea nitrogen / 2.8)
	Normal = 280 to 295 mOsm per kg
	In patients with hyperglycemia, uncorrected sodium should be used to calculate the osmolality
	Online calculators available at http://www.mdcalc.com/serum-osmolality-osmolarity and http://www.medcalc.com/osmol.html
Sodium deficit	Total body water % × weight in kg × (desired sodium − actual sodium)
	For total body water %, use 0.6 for men and 0.5 for women
	Example: for a 70-kg man with a serum sodium level of 120 mEq per L and a desired serum sodium level of 140 mEq per L, the calculation is 0.6 × 70 (140 − 120) = 42 × 20 = 840 mEq
	Online calculator available at http://www.mdcalc.com/sodium-deficit-in-hyponatremia
Water deficit	Volume (L) = (total body water %) × weight in kg × [(sodium − 140) / 140]
	For total body water %, use 0.45 for women older than 65 years, 0.5 for women 65 years and younger and for men older than 65 years, and 0.6 for men 65 years and younger and for children
	Example: for a 70-kg man with a serum sodium level of 120 mEq per L, the calculation is 0.6 × 70 × ([120 − 140] / 140) = 42 × (−20 / 140) = 42 × (−1 / 7) = −6 L
	Online calculators available at http://www.mdcalc.com/free-water-deficit-in-hypernatremia and http://www.medcalc.com/freewater.html