1. What is Osmolality?

Osmolality measures the concentration of dissolved particles in blood. The normal calculated osmolality range is 275-295 mOsm/kg. It helps evaluate fluid and electrolyte balance, and detect toxins or osmolar gaps.

2. How is Osmolality Calculated?

The standard calculation formula is:

Where:

• \( \text{Na} \) — Sodium in mEq/L
• \( \text{Glucose} \) — Glucose in mg/dL
• \( \text{BUN} \) — Blood Urea Nitrogen in mg/dL

Explanation: The equation accounts for major osmotically active particles in blood plasma.

3. Clinical Significance

Details: Osmolality is important for diagnosing and monitoring conditions like dehydration, diabetes insipidus, SIADH, and toxic alcohol ingestions (when comparing measured vs calculated osmolality).

4. Using the Calculator

Tips: Enter sodium, glucose, and BUN values in their standard units. The calculator will compute the osmolality and compare it to the normal range.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between osmolality and osmolarity?
A: Osmolality is per kilogram of solvent (more accurate), while osmolarity is per liter of solution. In clinical practice, they're often used interchangeably.

Q2: What causes high osmolality?
A: Hyperglycemia, uremia, hypernatremia, or presence of exogenous osmoles like ethanol, methanol, or ethylene glycol.

Q3: What causes low osmolality?
A: Hyponatremia, SIADH, or pseudohyponatremia from hyperlipidemia or hyperproteinemia.

Q4: What is osmolar gap?
A: Difference between measured and calculated osmolality (>10 mOsm/kg suggests unmeasured osmoles like toxic alcohols).

Q5: When is osmolality testing needed?
A: For evaluating hyponatremia, polyuria/polydipsia, altered mental status, or suspected toxic alcohol ingestion.