Chemistry

Calculated Serum Osmolality

Estimated osmolality from electrolytes.

Education and reference only. Not a substitute for clinical judgement, local policy or product labelling. Always verify before clinical use. Values are calculated in your browser and never stored.

When to use

Use to estimate serum osmolality and, compared with a measured value, to detect an osmolar gap (e.g. toxic alcohols).

Why use

A raised osmolar gap suggests unmeasured osmoles such as methanol or ethylene glycol.

Critical actions

Calculated osmolality = 2×Na + glucose + urea (mmol/L). Compare with a measured osmolality to calculate the osmolar gap (normal <10).

Evidence & references

Standard calculated osmolality formula (mmol/L units).

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