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 useful in diagnosing conditions like dehydration, diabetes insipidus, and toxic alcohol poisoning.

2. How Does the Calculator Work?

The calculator uses the serum osmolality equation:

Where:

• \( Na \) — Serum sodium (mmol/L)
• \( Glucose \) — Serum glucose (mg/dL)
• \( BUN \) — Blood urea nitrogen (mg/dL)

Explanation: The equation accounts for the major contributors to serum osmolality: sodium (and its accompanying anions), glucose, and urea.

3. Importance of Serum Osmolality

Details: Serum osmolality is crucial for assessing water balance disorders, evaluating patients with altered mental status, and monitoring treatment for conditions like hyperglycemia or toxic alcohol ingestion.

4. Using the Calculator

Tips: Enter serum sodium in mmol/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 the normal range for serum osmolality?
A: Normal serum osmolality ranges from 275-295 mOsm/kg. Values outside this range may indicate water balance disorders.

Q2: What is osmolal gap?
A: Osmolal gap is the difference between measured and calculated osmolality. An elevated gap (>10 mOsm/kg) suggests the presence of unmeasured osmoles like ethanol or methanol.

Q3: Why isn't potassium included in the equation?
A: Potassium concentration is much lower than sodium and its contribution to osmolality is minimal compared to the major contributors.

Q4: How does hyperglycemia affect osmolality?
A: High glucose levels increase serum osmolality. For every 100 mg/dL increase in glucose, osmolality increases by about 5.5 mOsm/kg.

Q5: When is measured osmolality needed?
A: Measured osmolality is needed when toxic alcohol ingestion is suspected or when the osmolal gap needs to be calculated.