1. What is Serum Osmolality?

Serum osmolality is a measure of 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 poisoning.

2. How Does the Calculator Work?

The calculator uses the serum osmolality equation:

Where:

• \( Na \) — Sodium concentration (mmol/L)
• \( Glucose \) — Glucose concentration (mg/dL)
• \( BUN \) — Blood urea nitrogen (mg/dL)

Explanation: The equation accounts for the major osmotically active particles in serum. Sodium is doubled to account for accompanying anions.

3. Clinical Importance

Details: Serum osmolality is crucial for assessing water balance, diagnosing hyponatremia, evaluating mental status changes, and screening for toxic alcohol ingestion.

4. Using the Calculator

Tips: Enter sodium in mmol/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 pathology.

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

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

Q4: When is this calculation most useful?
A: Particularly valuable in evaluating hyponatremia, polyuria/polydipsia syndromes, and altered mental status.

Q5: How does this relate to tonicity?
A: Calculated osmolality approximates tonicity when BUN is normal, as urea is an ineffective osmole.