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, and toxic alcohol ingestion.

2. How Does the Calculator Work?

The calculator uses the 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. Clinical Importance

Details: Serum osmolality is crucial for assessing water balance, diagnosing hyponatremia, evaluating mental status changes, and screening for toxic alcohol ingestion (when osmolal gap is calculated).

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/electrolyte disorders.

Q2: What is osmolal gap?
A: Osmolal gap = measured osmolality - calculated osmolality. A gap >10 suggests 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 accompanying anions (mainly chloride and bicarbonate) that maintain electroneutrality.

Q4: When is this calculation most useful?
A: Most useful in evaluating hyponatremia, polyuria/polydipsia syndromes, and altered mental status of unknown cause.

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