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Renal

Calculated Serum Osmolality

Estimates serum osmolality from sodium, glucose and urea — compare with a measured value to derive the osmolar gap.

Written for clinicians. If you're a parent or patient, don't act on these numbers — talk to your child's doctor.

Scope: Uses US conventional units (glucose & BUN in mg/dL). For SI units use 2×Na + glucose + urea (all mmol/L).

Inputs

FieldUnitNotes
Sodium mEq/L 100–200
Glucose mg/dL 0–2000
Blood urea nitrogen (BUN) mg/dL 0–300
Ethanol (optional) mg/dL Leave blank if not measured

FAQ

What is the Calculated Serum Osmolality?

Estimates serum osmolality from sodium, glucose and urea — compare with a measured value to derive the osmolar gap.

What inputs does the Calculated Serum Osmolality need?

Sodium (mEq/L), Glucose (mg/dL), Blood urea nitrogen (BUN) (mg/dL), Ethanol (optional) (mg/dL).

Are there any limitations?

Uses US conventional units (glucose & BUN in mg/dL). For SI units use 2×Na + glucose + urea (all mmol/L).

Related guides

Calculated Serum Osmolality and the Osmolar Gap: Screening for Toxic Alcohols

Estimating serum osmolality from sodium, glucose and urea, then comparing with a measured value — the formula, when the osmolar gap points to an unmeasured osmole, a worked example, and the gap's blind spots.

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