- 1). Multiply the amount of sodium within the specimen by two.
- 2). Divide the amount of glucose by 18.
- 3). Divide the amount of blood urea nitrogen by 2.8.
- 4). Add all three products together. This is the serum osmolarity of the specific blood sample per liter.
- 5). Multiply the resulting sum by 0.995. This converts the serum osmolality to serum osmolarity. Osmolality is a measure of serum osmotic concentration in terms of mass, while osmolarity is a measure of serum osmotic concentration per volume. This final calculation multiplies the osmolality by the mass density of blood times the result of the density of blood plasma (1.025 g/ml) minus the anhydrous solute concentration (0.03g/ml) to produce osmolarity.
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