🧬Biology 🧪Chemistry 💵Finance 🏥Health ➕Math

Osmolal Gap Calculator

Calculate the difference between measured and calculated serum osmolality to screen for toxic alcohol ingestions.

🧪

Input Parameters

Enter details for calculation.

Measured Osmolality (mOsm/kg)

Sodium (mEq/L)

BUN (mg/dL)

Glucose (mg/dL)

Osmolal Gap

15.6 mOsm/kg

Elevated (>10)

💡

Expert Tip

An osmolal gap > 10 mOsm/kg suggests the presence of unmeasured active osmoles like methanol, ethylene glycol, or isopropyl alcohol.

Calculation Methodology & Details

📐

Formula

Calculated = 2×Na + Glucose/18 + BUN/2.8 Gap = Measured − Calculated

Evaluates the difference to flag toxic ingestion gap.

📢

Important Disclaimer

The calculations provided are for educational and general informational purposes only. They do not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider.

How Osmolal Gap is Calculated

Follow these steps to use this calculator:

Input Labs

Measured osmolality, sodium, BUN, and glucose.

Read Gap

Normal is ≤ 10 mOsm/kg.

Related Calculators

View All Health Tools →

FLUIDS

Plasma Osmolality

Serum osmolality.

Launch Tool

Detailed Insights & Expert Guide

ℹ️ About this Calculation

This clinical electrolyte and fluid resuscitation calculator assists healthcare professionals with osmolality assessment, electrolyte deficit calculations, IV infusion rate adjustments, and fluid management protocols based on intensive care guidelines.

Variable Glossary

Input

Serum & Fluid Metrics

Serum sodium, potassium, calcium, glucose, BUN, albumin, patient body weight, or IV volume parameters.

Parameter

Resuscitation Targets

Corrected serum sodium/calcium, free water deficit (L), hourly IV drip rate (mL/hr), and calculated osmolality (mOsm/kg).

How to Calculate Step-by-Step

Step 1

Enter current serum electrolyte levels, blood chemistry lab results, or total IV volume ordered.

Step 2

Input patient weight and clinical correction factors (such as hyperglycemic sodium adjustment or albumin level).

Step 3

Review calculated deficit totals, corrected electrolyte values, and recommended IV infusion rates.

FAQ

Why is sodium correction necessary in hyperglycemia?

Elevated blood glucose shifts water from intracellular to extracellular spaces, artificially diluting serum sodium. Corrected sodium accounts for this osmotic shift (adding ~1.6 to 2.0 mEq/L per 100 mg/dL glucose over 100 mg/dL).

How is maintenance fluid calculated using the Holliday-Segar method?

The 4-2-1 rule allocates 4 mL/kg/hr for the first 10 kg of body weight, 2 mL/kg/hr for the next 10 kg, and 1 mL/kg/hr for each remaining kg.

Can fluid deficit calculators replace clinical re-evaluation?

No. Electrolyte replacement and fluid correction require continuous clinical monitoring, serial blood labs, and careful rate control to prevent complications like central pontine myelinolysis or cerebral edema.