1. What is the Osmolality Calculation Formula?

The osmolality calculation formula estimates serum osmolality using sodium, glucose, and blood urea nitrogen (BUN) values. It provides an assessment of the body's fluid balance and osmotic concentration.

2. How Does the Calculator Work?

The calculator uses the osmolality formula:

Where:

• \( Osm \) — Calculated osmolality (mOsm/kg)
• \( Na \) — Sodium concentration (mEq/L)
• \( Glucose \) — Glucose concentration (mg/dL)
• \( BUN \) — Blood urea nitrogen concentration (mg/dL)

Explanation: The formula accounts for the major osmotically active substances in plasma, with conversion factors to standardize units.

3. Importance of Osmolality Calculation

Details: Osmolality calculation is important for evaluating fluid and electrolyte balance, diagnosing dehydration, monitoring diabetes patients, and assessing toxic alcohol ingestion.

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 normal osmolality range?
A: Normal serum osmolality ranges from 275-295 mOsm/kg. Values outside this range may indicate fluid imbalance.

Q2: Why are glucose and BUN divided by 18 and 2.8 respectively?
A: These conversion factors account for molecular weights and convert mg/dL concentrations to mmol/L equivalents for osmolality calculation.

Q3: When should osmolality be measured?
A: Osmolality should be assessed in cases of suspected dehydration, diabetes complications, alcohol intoxication, or electrolyte disorders.

Q4: Are there limitations to this calculation?
A: This formula doesn't account for other osmotically active substances like ethanol, methanol, or ethylene glycol, which may be important in toxicology cases.

Q5: What is the osmolar gap?
A: The osmolar gap is the difference between measured osmolality and calculated osmolality. A gap > 10 mOsm/kg suggests the presence of unmeasured osmoles.