1. What is Osmolarity?

Definition: Osmolarity is a measure of solute concentration, defined as the number of osmoles of solute per liter of solution.

Purpose: It helps clinicians assess a patient's hydration status and evaluate electrolyte imbalances.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• Osmolarity — Concentration (mOsm/L)
• Na — Sodium (mmol/L)
• K — Potassium (mmol/L)
• Glucose — Glucose (mg/dL)
• BUN — Blood urea nitrogen (mg/dL)

Explanation: The formula accounts for the major osmotically active particles in blood plasma.

3. Clinical Importance

Details: Normal serum osmolarity ranges from 275-295 mOsm/L. Values outside this range may indicate dehydration, water intoxication, or other metabolic disturbances.

4. Using the Calculator

Tips: Enter the patient's sodium, potassium, glucose, and BUN values. All values must be ≥ 0 (potassium, glucose, and BUN can be 0).

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between osmolarity and osmolality?
A: Osmolarity is per liter of solution, while osmolality is per kilogram of solvent. They're nearly equal for dilute solutions like blood.

Q2: Why are sodium and potassium multiplied by 2?
A: This accounts for their associated anions (chloride, bicarbonate) which maintain electrical neutrality.

Q3: What does an elevated osmolarity indicate?
A: May suggest dehydration, hyperglycemia, uremia, or ingestion of osmotically active substances like ethanol.

Q4: How accurate is this calculated osmolarity?
A: It estimates the osmolar gap (difference between measured and calculated osmolarity) which helps identify unmeasured osmoles.

Q5: When is this calculation most useful?
A: In evaluating patients with altered mental status, suspected electrolyte disorders, or possible toxic alcohol ingestion.