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 identifying conditions like dehydration, diabetes insipidus, or 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 associated anions), glucose, and urea.

3. Clinical Importance

Details: Serum osmolality is crucial for diagnosing and managing fluid disorders, evaluating mental status changes, and assessing for osmolar gaps that might indicate toxic alcohol ingestion.

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?
A: Normal range is typically 275-295 mOsm/kg. Values outside this range may indicate fluid or electrolyte disorders.

Q2: What is an osmolar gap?
A: The difference between measured and calculated osmolality. A gap >10 suggests unmeasured osmoles (e.g., ethanol, methanol, ethylene glycol).

Q3: Why isn't potassium included in the equation?
A: Potassium concentration is much lower than sodium and has minimal effect on total osmolality.

Q4: How does hyperglycemia affect osmolality?
A: Glucose contributes to osmolality, with severe hyperglycemia causing significant increases and potentially hyperosmolar states.

Q5: When is direct osmolality measurement needed?
A: When toxic alcohol ingestion is suspected or when the calculated osmolality doesn't match clinical findings.