1. What is Osmolality?

Osmolality is a measure of the number of osmoles of solute per kilogram of solvent. In clinical medicine, it's used to evaluate the body's water balance and the concentration of particles in body fluids.

2. How Does the Calculator Work?

The calculator uses the following 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 contributors to serum osmolality: sodium (and accompanying anions), glucose, and urea.

3. Clinical Importance of Osmolality

Details: Osmolality is crucial for assessing fluid and electrolyte balance, diagnosing disorders like diabetes insipidus, and evaluating toxic alcohol ingestions (osmolar gap).

4. Using the Calculator

Tips: Enter sodium in mmol/L, glucose and BUN in mg/dL. All values must be valid positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a normal osmolality range?
A: Normal serum osmolality is typically 275-295 mOsm/kg. Values outside this range may indicate water imbalance.

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

Q3: Why is sodium multiplied by 2?
A: Sodium is accompanied by anions (mainly chloride) in serum, so each sodium ion effectively contributes two particles.

Q4: Are there limitations to this calculation?
A: It doesn't account for other osmoles like ethanol or mannitol. For precise measurement, laboratory osmometry is needed.

Q5: How does hyperglycemia affect osmolality?
A: High glucose increases osmolality and can cause osmotic diuresis. In hyperglycemia, corrected sodium should be used.