1. What is the Osmolality Equation?

The osmolality equation estimates plasma osmolality from sodium, glucose, and BUN values. It's used to evaluate fluid and electrolyte balance, and to detect osmolar disorders like hyperosmolality or hypo-osmolality.

2. How Does the Calculator Work?

The calculator uses the osmolality equation:

Where:

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

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

3. Importance of Osmolality Calculation

Details: Osmolality is crucial for diagnosing and managing fluid disorders, evaluating dehydration, assessing renal concentrating ability, and detecting toxic alcohol ingestions.

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 osmolality range?
A: Normal plasma osmolality is 275-295 mOsm/kg. Values outside this range indicate abnormal fluid balance.

Q2: What's the difference between osmolality and osmolarity?
A: Osmolality is measured per kg of solvent (more accurate), while osmolarity is per liter of solution. They're nearly equal in dilute solutions.

Q3: When is osmolal gap significant?
A: An osmolal gap >10 suggests unmeasured osmoles (e.g., ethanol, methanol, ethylene glycol, or other toxins).

Q4: Does this equation account for all osmoles?
A: No, it only includes major contributors. Measured osmolality (by freezing point depression) may differ slightly.

Q5: How does hyperglycemia affect osmolality?
A: Glucose contributes directly to osmolality. Very high glucose significantly increases plasma osmolality.