calculate_serum_osmolality: Serum Osmolality/Osmolarity Calculator

In cliot: Clinical Indices and Outcomes Tools

Serum Osmolality/Osmolarity Calculator

Description

Calculates the estimated serum osmolality (or osmolarity) based on serum sodium, glucose, and blood urea nitrogen (BUN). Optionally includes ethanol concentration if ingestion is suspected. This calculation is useful for determining the osmolal gap when compared to measured osmolality.

Usage

calculate_serum_osmolality(sodium, glucose, bun, ethanol = 0,
                           glucose_units = "mg/dL", bun_units = "mg/dL",
                           ethanol_units = "mg/dL")

Arguments

sodium	Numeric. Serum Sodium level in mEq/L or mmol/L.
glucose	Numeric. Serum Glucose level.
bun	Numeric. Blood Urea Nitrogen level.
ethanol	Numeric (Optional). Serum Ethanol level. Defaults to 0.
glucose_units	String. Units for glucose input. Options: "mg/dL" (default) or "mmol/L".
bun_units	String. Units for BUN input. Options: "mg/dL" (default) or "mmol/L".
ethanol_units	String. Units for ethanol input. Options: "mg/dL" (default) or "mmol/L".

Details

The formula used (for mg/dL inputs) is:

Osmolality = (2 \times Na) + \frac{Glucose}{18} + \frac{BUN}{2.8} + \frac{Ethanol}{4.6}

If inputs are in mmol/L, the terms are simply summed (Ethanol factor may vary slightly in different literature but 4.6 divisor for mg/dL is standard).

Value

A list containing:

Calculated_Osmolality

The estimated serum osmolality in mOsm/kg H2O.

References

Purssell RA, Pudek M, Brubacher J, Abu-Laban RB. Derivation and validation of a formula to calculate the contribution of ethanol to the osmolal gap. Ann Emerg Med. 2001;38(6):653-659. doi:10.1067/mem.2001.119455

Examples

# Example 1: Standard Labs (mg/dL)
# Na 140, Glucose 100, BUN 15, No Ethanol
# Calc = 280 + 5.5 + 5.4 = 290.9
calculate_serum_osmolality(140, 100, 15)

# Example 2: Ethanol Intoxication
# Na 135, Glucose 90, BUN 10, Ethanol 100 mg/dL
# Calc = 270 + 5 + 3.6 + 21.7 = 300.3
calculate_serum_osmolality(135, 90, 10, 100)

cliot documentation built on Dec. 1, 2025, 1:06 a.m.