1. What is Serum Osmolality?

Serum osmolality is a measure of the number of dissolved particles in blood. It helps evaluate the body's water balance and is particularly useful in assessing conditions like dehydration, poisoning, and abnormal sodium levels.

2. How Does the Calculator Work?

The calculator uses the serum osmolality equation:

Where:

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

Explanation: The equation accounts for the major osmotically active substances in blood, with each component having its own conversion factor based on molecular weight.

3. Importance of Osmolality Calculation

Details: Osmolality is crucial for diagnosing and managing conditions like water intoxication, diabetes insipidus, syndrome of inappropriate antidiuretic hormone (SIADH), and toxic alcohol ingestion.

4. Using the Calculator

Tips: Enter all values in their respective units. Sodium is required, while other values can be zero if not applicable. Normal serum osmolality ranges from 275-295 mOsm/kg.

5. Frequently Asked Questions (FAQ)

Q1: 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.

Q2: What is the osmolar gap?
A: The difference between measured and calculated osmolality. A gap >10 suggests unmeasured osmoles like methanol or ethylene glycol.

Q3: Why include ethanol in the calculation?
A: Ethanol is osmotically active and can significantly affect osmolality in cases of alcohol intoxication.

Q4: What are common causes of high osmolality?
A: Dehydration, hyperglycemia, uremia, alcohol intoxication, and ingestion of toxic alcohols.

Q5: When is osmolality most clinically useful?
A: In evaluating altered mental status, suspected toxic alcohol ingestion, and disorders of water balance.