How is serum osmolality calculated?

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How is serum osmolality calculated?

Osmolality reflects how many osmotically active particles are present in serum. The main contributors are sodium with its accompanying anions, plus glucose and urea. To capture the sodium part, we count two particles for each sodium ion (one for Na+ and one for the counterions like Cl− or HCO3−). Then we add glucose and urea as their own solute particles. When the concentrations are in mmol/L, the standard estimate is 2 × Na + Glucose + Urea. Potassium’s contribution is smaller and isn’t included in this simple equation. This is why the expression using 2 × Na plus Glucose plus Urea is the right way to calculate serum osmolality.

Osmolality reflects how many osmotically active particles are present in serum. The main contributors are sodium with its accompanying anions, plus glucose and urea. To capture the sodium part, we count two particles for each sodium ion (one for Na+ and one for the counterions like Cl− or HCO3−). Then we add glucose and urea as their own solute particles. When the concentrations are in mmol/L, the standard estimate is 2 × Na + Glucose + Urea. Potassium’s contribution is smaller and isn’t included in this simple equation. This is why the expression using 2 × Na plus Glucose plus Urea is the right way to calculate serum osmolality.

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