This tool estimates the concentration of particles in the blood based on three primary solutes: sodium, glucose, and blood urea nitrogen (BUN). It is used clinically to assess hydration status and electrolyte balance.
Estimated Serum Osmolality:
290 mOsm/kg
Note: The normal range for serum osmolality is typically 275–295 mOsm/kg. Significant deviations may indicate dehydration, overhydration, or presence of other solutes.
Osmolality is a laboratory test that measures the concentration of all chemical particles found in the fluid part of blood. It primarily reflects the body's water-electrolyte balance and helps clinicians assess hydration status.
Formula: 2[Na] + [Glucose]/18 + [BUN]/2.8
Suppose a patient has the following laboratory results: Sodium = 140 mEq/L, Glucose = 180 mg/dL, and BUN = 28 mg/dL.
What is a normal serum osmolality?A normal range for healthy adults is typically between 275 and 295 mOsm/kg.
What is the osmolal gap?The osmolal gap is the difference between the measured osmolality (from the lab) and the calculated osmolality. A gap >10 suggests the presence of unmeasured solutes like alcohol.
Why divide glucose by 18?In many regions, glucose is measured in mg/dL. Dividing by 18 converts this value to mmol/L, which is the unit required for the standard osmolality equation.
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