1. What is Serum Osmolality?

Serum osmolality measures the concentration of dissolved particles in blood. It's important for assessing fluid balance, electrolyte disorders, and conditions like diabetes insipidus or syndrome of inappropriate antidiuretic hormone (SIADH).

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 (mg/dL)

Explanation: The equation accounts for the major osmotically active substances in blood. Sodium is doubled because it's accompanied by anions (mainly chloride).

3. Importance of Osmolality Calculation

Details: Serum osmolality is crucial for diagnosing and managing fluid and electrolyte disorders, evaluating renal function, and assessing acid-base balance.

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

Q2: What's the difference between osmolality and osmolarity?
A: Osmolality measures particles per kilogram of solvent (more accurate), while osmolarity measures particles per liter of solution.

Q3: When is osmolality measurement important?
A: Important in cases of hyponatremia, hypernatremia, altered mental status, suspected poisoning, or evaluation of polyuria/polydipsia.

Q4: What is the osmolal gap?
A: Difference between measured and calculated osmolality. An elevated gap (>10) suggests unmeasured osmoles like alcohols, toxins, or medications.

Q5: Does this equation account for all osmotically active substances?
A: No, it's an estimation. Other substances like ethanol, methanol, or ethylene glycol aren't included but contribute to measured osmolality.