The formula for calculating blood osmolarity estimates the concentration of dissolved particles in the blood. There are a couple of variations, both based on readily available lab results.
Here are the common formulas used to calculate blood osmolarity:
- Formula 1: Calculated osmolarity = 2 (Na+) + 2 (K+) + Glucose + Urea (all in mmol/L)
- Formula 2: Calculated osmolarity = 2 (Na+) + Glucose + Urea (all in mmol/L)
These formulas provide an estimation, and the actual measured osmolarity might differ. Sodium (Na+), potassium (K+), glucose, and urea are major contributors to the osmotic pressure of blood. All components in the formula are measured in mmol/L (millimoles per liter). The multiplying factor of 2 accounts for the anions (like chloride and bicarbonate) that accompany sodium and potassium in the extracellular fluid, maintaining electrical neutrality.
