Calculates the osmolal gap from measured and calculated serum osmolality using SI units.
Osmolal Gap (SI Units): Clinical Guide
Browse Knowledge HubCalculates the osmolal gap from measured and calculated serum osmolality using SI units.
Overview
Calculates the osmolal gap from measured and calculated serum osmolality using SI units.
Clinical Significance
An increased gap may suggest unmeasured osmoles but is neither sensitive nor specific for toxic alcohol exposure.
When to Use
- Use when the required measurements are available, reliable and clinically relevant.
How It Is Calculated
- Osmolal gap = measured osmolality − (2 × sodium + glucose + urea).
Interpretation
- An increased gap may suggest unmeasured osmoles but is neither sensitive nor specific for toxic alcohol exposure.
Worked Example
Enter valid values in the displayed units. MedicalC then applies: Osmolal gap = measured osmolality − (2 × sodium + glucose + urea).
Limitations
- The result does not establish a diagnosis or mandate treatment.
- Measurement error may be more important than arithmetic precision.
- Published thresholds may differ between populations and settings.
Clinical Pearls
- Document the source values and units with the final result.
- Review trends rather than isolated values where appropriate.
Common Mistakes
- Using the wrong unit.
- Combining values from different time points.
- Applying the result outside the intended measurement or clinical context.
Frequently Asked Questions
What does this calculator provide?
Calculates the osmolal gap from measured and calculated serum osmolality using SI units.
What formula is used?
Osmolal gap = measured osmolality − (2 × sodium + glucose + urea).
Can the result be used alone?
No. It must be interpreted with the full clinical assessment and appropriate investigations.
What is the main limitation?
The result depends on accurate source measurements, correct units and appropriate clinical applicability.
References
- Kraut JA, Kurtz I. Toxic alcohol ingestions: clinical features, diagnosis, and management. Clin J Am Soc Nephrol. 2008. — Primary, supporting or authoritative reference for the implemented relationship.
Reviewed by: MedicalC Clinical Editorial Team
Last reviewed: July 2026
Clinical Disclaimer
MedicalC calculators and clinical tools are intended to support healthcare professionals. They do not replace clinical judgement, individual patient assessment, local guidance or specialist advice.
Results should always be interpreted in the context of the patient’s history, examination, investigations, current clinical condition and applicable professional guidance.