1. What is Plasma Osmolality?

Plasma osmolality measures the concentration of dissolved particles in blood plasma. It's important for evaluating fluid and electrolyte balance, and for diagnosing conditions like dehydration, diabetes insipidus, and poisoning.

2. How Does the Calculator Work?

The calculator uses the standard plasma osmolality equation:

Where:

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

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

3. Clinical Importance

Details: Normal plasma osmolality is 275-295 mOsm/kg. Values outside this range may indicate water imbalance, electrolyte disorders, or toxic 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's the difference between osmolality and osmolarity?
A: Osmolality is measured per kilogram of solvent (more accurate), while osmolarity is per liter of solution. In clinical practice, the terms are often used interchangeably.

Q2: When is this calculation most useful?
A: For evaluating hyponatremia, monitoring therapy for osmolar disorders, and assessing for toxic alcohol ingestion.

Q3: What's the osmolar gap?
A: The difference between measured and calculated osmolality. A gap >10 suggests unmeasured osmoles (e.g., methanol, ethylene glycol).

Q4: Does this account for all osmotically active particles?
A: No, it's an approximation. Other substances like potassium, calcium, and magnesium also contribute but are typically minor.

Q5: How does hyperglycemia affect osmolality?
A: Glucose is osmotically active and increases plasma osmolality directly. Very high glucose can cause osmotic diuresis.