1. What is Serum Osmolality?

Serum osmolality measures the concentration of dissolved particles in blood. It's important for assessing electrolyte and water balance, and for evaluating conditions like dehydration, diabetes insipidus, and toxic alcohol ingestion.

2. How Does the Calculator Work?

The calculator uses the serum osmolality equation:

Where:

• \( Na^+ \) — Serum sodium concentration (mmol/L)
• \( Glucose \) — Serum glucose concentration (mg/dL)
• \( BUN \) — Blood urea nitrogen concentration (mg/dL)

Explanation: The equation accounts for the major osmotically active particles in blood: sodium (and its associated anions), glucose, and urea.

3. Importance of Osmolality Calculation

Details: Calculating serum osmolality helps evaluate fluid balance, diagnose electrolyte disorders, and assess for the presence of osmolar gaps which may indicate toxic alcohol ingestion.

4. Using the Calculator

Tips: Enter sodium in mmol/L, glucose and BUN in mg/dL. All values must be valid (sodium > 0, glucose and BUN ≥ 0).

5. Frequently Asked Questions (FAQ)

Q1: What is a normal serum osmolality range?
A: Normal range is typically 275-295 mOsm/kg. Values outside this range may indicate fluid or electrolyte imbalances.

Q2: What is an osmolar gap?
A: The difference between measured and calculated osmolality. A gap >10 suggests unmeasured osmoles like ethanol, methanol, or ethylene glycol.

Q3: Why multiply sodium by 2?
A: Sodium is paired with anions (mainly chloride and bicarbonate) in serum, so each sodium ion is associated with one anion, effectively doubling its osmotic contribution.

Q4: Does this equation account for potassium?
A: No, potassium's contribution is minor compared to sodium and is typically omitted from this calculation.

Q5: When is measured osmolality needed?
A: When toxic alcohol ingestion is suspected or when the calculated osmolality doesn't match clinical findings.