1. What is Serum Osmolality?

Serum osmolality is a measure of the number of dissolved particles in blood serum. It's important for evaluating fluid and electrolyte balance, particularly in conditions like dehydration, diabetes, and poisoning.

2. How Does the Calculator Work?

The calculator uses the standard 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 contributors to serum osmolality: sodium (and its associated anions), glucose, and urea.

3. Clinical Importance

Details: Serum osmolality is used to evaluate water balance, diagnose disorders like diabetes insipidus, assess dehydration, and screen for toxic alcohol ingestion (osmolal gap).

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 osmolal gap?
A: The difference between measured and calculated osmolality. A gap >10 suggests unmeasured osmoles (e.g., 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: How does hyperglycemia affect osmolality?
A: High glucose increases serum osmolality, which can lead to osmotic diuresis and dehydration.

Q5: When is direct osmolality measurement preferred?
A: When evaluating for toxic alcohol ingestion or when the patient has abnormal serum components not included in the calculation.