1. What Is Osmolality?

Osmolality is a measure of the number of dissolved particles in a fluid. It's an important indicator of the body's water balance and kidney function.

2. Normal Osmolality Range

The normal range for serum osmolality is:

Key Points:

• Values below 275 mOsm/kg indicate hypoosmolality
• Values above 295 mOsm/kg indicate hyperosmolality
• Maintained within narrow range by homeostasis

3. Clinical Significance

Details: Osmolality helps evaluate hydration status, diagnose electrolyte imbalances, and assess kidney function. Abnormal levels may indicate conditions like diabetes insipidus or SIADH.

4. Factors Affecting Osmolality

Influencing Factors: Water intake, sodium levels, glucose levels, urea concentration, and kidney function all affect osmolality measurements.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between osmolality and osmolarity?
A: Osmolality measures particles per kilogram of solvent (more accurate), while osmolarity measures per liter of solution.

Q2: How is osmolality measured?
A: Can be measured directly by freezing point depression or calculated from sodium, glucose, and BUN values.

Q3: When should osmolality be tested?
A: When evaluating hyponatremia, polyuria, or suspected poisoning (e.g., ethanol, methanol).

Q4: What causes high osmolality?
A: Dehydration, hyperglycemia, uremia, or ingestion of alcohols like ethanol or methanol.

Q5: What causes low osmolality?
A: Overhydration, SIADH, or conditions causing water retention.