1. What is Serum Osmolality?

Serum osmolality measures the concentration of dissolved particles in blood. It's important for evaluating fluid and electrolyte balance, and for diagnosing conditions like dehydration, diabetes insipidus, or toxin ingestion.

2. How Does the Calculator Work?

The calculator uses the standard serum osmolality equation:

Where:

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

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

3. Importance of Osmolality Calculation

Details: Serum osmolality helps assess water balance, diagnose electrolyte disorders, evaluate mental status changes, and monitor treatment effectiveness in conditions like diabetic ketoacidosis.

4. Using the Calculator

Tips: Enter sodium in mEq/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 serum osmolality range?
A: Normal range 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 unmeasured osmoles (e.g., ethanol, methanol, ethylene glycol).

Q3: Why is sodium multiplied by 2 in the equation?
A: Sodium is accompanied by anions (mainly chloride and bicarbonate) that contribute equally to osmolality.

Q4: When is osmolality most useful clinically?
A: In evaluating hyponatremia, polyuria/polydipsia syndromes, altered mental status, and suspected toxin ingestion.

Q5: Does this account for all osmotically active particles?
A: No, it's an estimate. Other particles (e.g., potassium, calcium, lipids) contribute minimally under normal circumstances.