1. What is Serum Osmolality?

Serum osmolality is a measure of the number of dissolved particles in blood serum. It helps evaluate the body's water balance and is useful in diagnosing conditions like dehydration, diabetes insipidus, and toxic alcohol poisoning.

2. How Does the Calculator Work?

The calculator uses the standard serum osmolality equation:

Where:

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

Explanation: The equation accounts for the major osmotically active substances in blood. Sodium is doubled to account for accompanying anions.

3. Importance of Osmolality Calculation

Details: Serum osmolality is crucial for assessing water balance disorders, evaluating hydration status, and detecting osmolar gaps that 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 water balance disorders.

Q2: What is the osmolar gap?
A: The difference between measured and calculated osmolality. A gap >10 suggests unmeasured osmoles (e.g., ethanol, methanol).

Q3: Why isn't ethanol included in this calculator?
A: This calculator is for the standard equation without ethanol. Separate calculators exist for ethanol-containing equations.

Q4: How does hyperglycemia affect osmolality?
A: High glucose increases serum osmolality significantly, which can lead to osmotic diuresis and dehydration.

Q5: When is direct osmolality measurement preferred?
A: When toxic alcohol ingestion is suspected, or when precise measurement is needed for clinical decision-making.