What is a normal serum osmolality?

Normal serum osmolality is 285-295 mOsm/kg. Elevated (>295) indicates hypertonicity; low (<285) indicates hypotonicity.

What is osmolal gap and what does it mean?

Osmolal gap = measured osmolality - calculated osmolality. Normal <10-15. Elevated gap suggests toxic alcohols (ethanol, methanol, ethylene glycol) or lactic acidosis.

How does osmolality differ from osmolarity?

Osmolality (per kg water) is measured by freezing point depression. Osmolarity (per L solution) is calculated. They are nearly identical in clinical practice.

Serum Osmolality Calculator

Calculate serum osmolality = 2×Na + glucose/18 + BUN/2.8 — detects osmolal gap suggesting unmeasured osmoles.

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Frequently Asked Questions

What is a normal serum osmolality?

What is osmolal gap and what does it mean?

How does osmolality differ from osmolarity?