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 concentration (mg/dL)

Explanation: The equation accounts for the major contributors to plasma osmolality: sodium (and its associated anions), glucose, and urea.

3. Importance of Osmolality Calculation

Details: Plasma osmolality is crucial for assessing water balance disorders, evaluating hydration status, and investigating causes of altered mental status.

4. Using the Calculator

Tips: Enter sodium in mmol/L, glucose in mg/dL, 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 plasma osmolality?
A: Normal range is typically 275-295 mOsm/kg. Values outside this range may indicate water imbalance or other disorders.

Q2: What's the difference between osmolality and osmolarity?
A: Osmolality measures particles per kilogram of solvent (more accurate), while osmolarity measures particles per liter of solution.

Q3: When is osmolality most useful clinically?
A: For evaluating hyponatremia, diagnosing diabetes insipidus, assessing dehydration, and screening for toxic alcohol ingestion.

Q4: What's the osmolar gap?
A: The difference between measured and calculated osmolality. An elevated gap (>10) may indicate unmeasured osmoles like ethanol, methanol, or ethylene glycol.

Q5: Does this equation account for all osmotically active particles?
A: No, it's an estimate. Other particles like potassium, calcium, and abnormal solutes (e.g., mannitol) also contribute but aren't included in this basic calculation.