1. What is Serum Osmolality?

Serum osmolality is a measure of the concentration of dissolved particles in blood serum. It's an important indicator of the body's water balance and helps evaluate hydration status, electrolyte balance, and kidney function.

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: This equation estimates the osmotic pressure of serum based on its major osmotically active constituents.

3. Importance of Serum Osmolality Calculation

Details: Serum osmolality is crucial for assessing fluid and electrolyte balance, diagnosing disorders like diabetes insipidus, syndrome of inappropriate antidiuretic hormone secretion (SIADH), and evaluating toxic alcohol ingestions.

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 the normal range for serum osmolality?
A: Normal serum osmolality ranges from 275 to 295 mOsm/kg. Values outside this range may indicate underlying medical conditions.

Q2: How does this calculated osmolality compare to measured osmolality?
A: The calculated value provides a good estimate, but measured osmolality (by freezing point depression) is more accurate, especially when unmeasured osmoles are present.

Q3: What is the osmolar gap?
A: The osmolar gap is the difference between measured and calculated osmolality. A gap greater than 10-15 mOsm/kg suggests the presence of unmeasured osmotically active substances.

Q4: When is serum osmolality testing indicated?
A: It's indicated when evaluating hyponatremia, polyuria-polydipsia syndromes, altered mental status, and suspected toxic alcohol ingestion.

Q5: Can medications affect serum osmolality?
A: Yes, certain medications like mannitol, radiocontrast agents, and some alcohols can increase serum osmolality.