1. What is Serum Osmolality?

Serum osmolality is a measure of the number of dissolved particles per kilogram of serum. It helps evaluate the body's water balance and is used to diagnose 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 (mEq/L)
• \( Glucose \) — Glucose concentration (mg/dL)
• \( BUN \) — Blood urea nitrogen (mg/dL)

Explanation: The equation accounts for the major osmotically active particles in blood: sodium (and its accompanying anions), glucose, and urea.

3. Importance of Osmolality Calculation

Details: Serum osmolality is crucial for assessing water balance disorders, evaluating the severity of hyperglycemia, and detecting osmolar gaps which may indicate the presence of toxic alcohols.

4. Using the Calculator

Tips: Enter sodium in mEq/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 balance disorders.

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

Q3: Why is sodium multiplied by 2 in the equation?
A: Sodium is accompanied by an equal amount of anions (mainly chloride and bicarbonate), 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 patients with these substances, measured osmolality is needed.

Q5: How does hyperglycemia affect osmolality?
A: High glucose increases serum osmolality. In diabetes, this can lead to hyperosmolar hyperglycemic state, a medical emergency.