1. What is Calculated Serum Osmolality?

Calculated serum osmolality is a measure of the concentration of dissolved particles in blood. It's used to evaluate fluid and electrolyte balance, and to identify conditions like dehydration, diabetes insipidus, or toxic alcohol ingestion.

2. How Does the Calculator Work?

The calculator uses the standard formula:

Where:

• \( Na \) — Sodium concentration (mEq/L)
• \( Glucose \) — Glucose concentration (mg/dL)
• \( BUN \) — Blood urea nitrogen concentration (mg/dL)

Explanation: The equation accounts for the major osmotically active particles in serum. Sodium is doubled to account for accompanying anions, while glucose and BUN are converted to mmol/L units.

3. Importance of Osmolality Calculation

Details: Serum osmolality is crucial for assessing water balance, diagnosing electrolyte disorders, and evaluating for osmolar gaps which may indicate toxic alcohol ingestion.

4. Using the Calculator

Tips: Enter sodium in mEq/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 disorders.

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 isn't potassium included in the formula?
A: Potassium's contribution is small and relatively constant, so it's typically omitted from this calculation.

Q4: How does this differ from measured osmolality?
A: Measured osmolality includes all solutes, while calculated estimates based on major contributors. The difference between them is the osmolar gap.

Q5: When is this calculation most useful?
A: Particularly valuable in evaluating altered mental status, suspected toxic alcohol ingestion, or disorders of water balance.