1. What is Serum Osmolality?

Serum osmolality measures the concentration of dissolved particles in blood. It's important for assessing electrolyte and water balance, and for evaluating conditions like dehydration, diabetes insipidus, and toxic alcohol ingestion.

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 concentration (mg/dL)

Explanation: The equation accounts for the major osmotically active particles in serum. Sodium is doubled to account for accompanying anions, while glucose and BUN are divided by conversion factors to express them in mmol/L.

3. Importance of Osmolality Calculation

Details: Osmolality helps evaluate fluid balance, diagnose electrolyte disorders, assess renal function, and detect osmolar gaps that may indicate 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 range?
A: Normal range is typically 275-295 mOsm/kg. Values outside this range may indicate water imbalance or other disorders.

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

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

Q4: When is osmolality most useful clinically?
A: For evaluating hyponatremia, polyuria/polydipsia syndromes, and suspected toxic alcohol ingestion.

Q5: How does this differ from urine osmolality?
A: Urine osmolality measures kidney's concentrating ability, while serum osmolality reflects overall body water balance.