Osmolar Gap Calculator

The Osmolar Gap Calculator estimates the difference between measured and calculated serum osmolality using Sodium, Glucose, BUN, and Alcohol levels. This tool helps medical professionals quickly detect toxic alcohol poisoning and unexplained metabolic acidosis. Whether you are managing emergency room cases, evaluating toxicology patients, or assessing unexplained anion gaps, this calculator provides rapid, evidence-based results to support critical clinical decisions.

Range: 120-160 mEq/L
Range: 50-400 mg/dL
Range: 5-50 mg/dL
Range: 250-350 mOsm/kg
Range: 0-500 mg/dL

How Osmolar Gap Is Calculated

The Osmolar Gap represents the difference between the actual concentration of particles in the blood and the expected concentration based on major solutes. This calculation relies on the standard clinical formula to ensure accuracy in toxicology screening.

Calculated Osmolality = (2 × Na+) + (Glucose/18) + (BUN/2.8) + (Ethanol/4.6)

Where:

  • Na+ is serum sodium (mEq/L)
  • Glucose is blood glucose (mg/dL)
  • BUN is blood urea nitrogen (mg/dL)
  • Ethanol is serum alcohol level (mg/dL)

First, the formula estimates serum osmolality by doubling sodium and adding converted values for glucose, BUN, and alcohol. This matters because sodium is the primary extracellular osmole, while the conversion factors adjust for the molecular weight of other substances. Finally, subtract this calculated number from the directly measured osmolality to find the gap. This method is a trusted clinical tool for identifying unmeasured osmotically active particles like toxins.

What Your Osmolar Gap Means

The Osmolar Gap indicates if there are hidden, unmeasured substances in the blood, such as toxic alcohols.

Normal Range (-10 to +10 mOsm/kg)

This range typically means no significant toxins are present. The measured osmolality is fully explained by sodium, glucose, and urea levels.

Mild Elevation (+10 to +20 mOsm/kg)

This may indicate early toxic ingestion or the presence of other osmotically active substances like mannitol. Monitor the patient closely for developing metabolic acidosis.

Significantly Elevated (>20 mOsm/kg)

A gap this high strongly suggests toxic alcohol poisoning, such as methanol or ethylene glycol. Immediate toxicology review and aggressive interventions like hemodialysis are often required to save the patient's life.

Important Note

Lab errors or very high lipid levels can sometimes falsely elevate the gap, so always correlate results with the patient's clinical picture.

Disclaimer: This tool is for educational and screening purposes only and is not a substitute for professional medical advice or diagnosis. Always consult a healthcare provider for interpreting lab results and managing treatment.

Re-measure the gap every 2-4 hours during treatment to effectively track the clearance of toxins.