1. What is the Osmolality Formula?

The osmolality formula estimates the concentration of solute particles in blood plasma. It's commonly used to evaluate fluid and electrolyte balance, and to detect conditions like dehydration, diabetes insipidus, or toxic alcohol ingestion.

2. How Does the Calculator Work?

The calculator uses the osmolality equation:

Where:

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

Explanation: The equation accounts for the major contributors to plasma osmolality. Sodium is doubled to account for accompanying anions, while glucose and BUN are divided by conversion factors.

3. Importance of Osmolality Calculation

Details: Calculated osmolality helps assess hydration status, diagnose electrolyte disorders, and detect osmolar gaps which may indicate the presence of unmeasured osmoles like ethanol, methanol, or ethylene glycol.

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 typically 275-295 mOsm/kg. Values outside this range may indicate fluid or electrolyte disorders.

Q2: What is the osmolar gap?
A: The difference between measured and calculated osmolality. A gap >10 suggests presence of unmeasured osmoles like alcohols or toxins.

Q3: Why isn't potassium included in the formula?
A: Potassium's contribution is relatively small and stable, so it's typically omitted from this calculation.

Q4: How does hyperglycemia affect osmolality?
A: High glucose significantly increases osmolality. Each 18 mg/dL of glucose adds approximately 1 mOsm/kg.

Q5: When is measured osmolality preferred?
A: When suspecting toxic alcohol ingestion or other conditions causing an osmolar gap, direct measurement is needed.