1. What is Serum Osmolality?

Serum osmolality is a measure of the number of dissolved particles per kilogram of serum. It helps evaluate the body's water balance and is important in assessing dehydration, overhydration, and certain toxic ingestions.

2. How Does the Calculator Work?

The calculator uses the serum osmolality equation:

Where:

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

Explanation: The equation accounts for the major osmotically active particles in serum: sodium (and its accompanying anions), glucose, and urea.

3. Importance of Osmolality Calculation

Details: Serum osmolality is crucial for diagnosing and managing fluid and electrolyte disorders, evaluating altered mental status, and assessing for toxic alcohol ingestion.

4. Using the Calculator

Tips: Enter sodium in mEq/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 serum osmolality?
A: Normal range is typically 275-295 mOsm/kg. Values outside this range may indicate water imbalance or the presence of unmeasured osmoles.

Q2: What is the osmolar gap?
A: The difference between measured and calculated osmolality. A gap >10 suggests the presence of unmeasured osmoles (e.g., ethanol, methanol, ethylene glycol).

Q3: Why multiply sodium by 2?
A: Sodium is multiplied by 2 to account for its accompanying anions (mainly chloride and bicarbonate) that maintain electroneutrality.

Q4: When is this calculation most useful?
A: Particularly helpful in evaluating altered mental status, suspected toxic alcohol ingestion, and disorders of water balance.

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